union bay place geotech report draft

DRAFT Geotechnical Engineering Design Report

Union Bay Place Development Seattle, Washington Prepared for

University Place, LLC November 19, 2015 19174‐00

1700 Westlake Avenue North, Suite 200

Seattle, Washington 98109-6212

Fax 206.328.5581

Tel 206.324.9530

DRAFT Geotechnical Engineering Design Report

Union Bay Place Development Seattle, Washington Prepared for

University Place, LLC November 19, 2015 19174‐00 Prepared by

Hart Crowser, Inc. Benjamin M. Blanchette, PE Geotechnical Engineer [email protected]

Garry E. Horvitz, PE, LEG Madan Karkee, PhD, PE Sr. Principal Geotechnical Engineer Sr. Associate Geotechnical Engineer [email protected] [email protected]

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Contents

INTRODUCTION 1

PURPOSE, SCOPE, AND THE USE OF THIS REPORT 1

PROJECT UNDERSTANDING 2

SUBSURFACE CONDITIONS 2

Soil Conditions 3 Groundwater 3 Hydraulic Conductivity (Slug Testing) 4

SEISMIC DESIGN RECOMMENDATIONS 5

Site Class 5 Liquefaction Assessment 6 Post‐Liquefaction Vertical Induced Settlement 7 Surface Rupture 7

GEOTECHNICAL ENGINEERING DESIGN RECOMMENDATIONS 7

General Considerations 7 Site Preparation 8 Pile Types 8 Augercast Pile Foundations 9

Vertical Pile Capacity 10 Lateral Pile Capacity 11 Passive Pressure on Pile Caps and Grade Beams 12 Augercast Pile Installation 12

Temporary Shoring 14 Lateral Earth Pressure 14 Soldier Pile Design 15 Soldier Pile Installation 15 Lagging 16 Tieback Anchor Design and Construction 17 Tieback Anchor Testing 18

Permanent Subgrade Walls 18 Lateral Earth Pressure Error! Bookmark not defined. Backfill Considerations Error! Bookmark not defined. Wall Drainage 19

Floor Slabs 19 Construction Dewatering 19

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Construction Dewatering Recommendations 19 Geotechnical Impacts of Dewatering 20

Permanent Drainage 21 Structural Fill 21

Use of On‐Site Soils as Structural Fill 22 Temporary Open Cuts 22 Utilities 23 Methane Venting 24

RECOMMENDATIONS FOR CONTINUING GEOTECHNICAL SERVICES 25

Design and Consulting Services 25 Construction Services 25

REFERENCES 26

TABLES 1 Groundwater Elevations 4

2 Seismic Design Parameters According to IBC 2012 6

3 Allowable Axial Capacity for Augercast Piles 10

4 Soil Parameters for LPILE Input (B‐3) 11

5 Pile P‐multipliers from AASHTO (2014) 11

Contents | iii

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FIGURES 1 Vicinity Map

2 Site and Exploration Plan

3 Generalized Subsurface Cross Section A‐A’

4 Generalized Subsurface Cross Section B‐B’

5 Cascadia Earthquake Sources

6 Regional Fault Zones

7 Design of Temporary Cantilever or Single‐Support Soldier Pile Shoring

8 Lateral Soil Pressure for Permanent Condition

9 Surcharge Pressures Determination of Lateral Pressure Acting on Adjacent Shoring

ATTACHMENT 1 Tieback Anchor Testing Program

ATTACHMENT 2 Shoring Monitoring Program

APPENDIX A Field Exploration Methods and Analysis

APPENDIX B Laboratory Testing Program

APPENDIX C Historical Explorations

APPENDIX D Slug Testing

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Geotechnical Engineering Design Report

Union Bay Place Development Seattle, Washington

INTRODUCTION This report presents our geotechnical engineering design recommendations for the proposed Union

Bay Place development in Seattle, Washington (Figure 1). The project is a new mid‐rise apartment

building at 4603 and 4609 Union Bay Place NE.

This report presents our geotechnical engineering recommendations and is organized as follows:

Introduction;

Purpose, Scope, and Use of This Report;

Project Understanding;

Subsurface Conditions;

Seismic Design Recommendations;

Geotechnical Engineering Design Recommendations; and

Recommendations for Continuing Geotechnical Services.

Following the report text we include:

Figures illustrating site information and presenting our recommendations;

Attachment 1, containing the tieback anchor testing program;

Attachment 2, containing the shoring monitoring program; and

Appendices containing the results of field exploration, laboratory testing, historical explorations,

and slug testing.

PURPOSE, SCOPE, AND USE OF THIS REPORT The purpose of our work was to assess subsurface information and provide geotechnical engineering

recommendations for design of the proposed Union Bay Place development. Our scope of work for

this project included:

Corresponding and meeting with the design team;

Reviewing historical geotechnical explorations;

Drilling one soil borings and collecting soil samples;

Installing two groundwater monitoring wells;

Conducting field slug testing for soil permeability;

Completing laboratory analysis on selected soil samples;

Performing engineering analysis; and

Providing engineering recommendations in this report.

2 | Union Bay Place Development

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We prepared this report for the exclusive use of University Place LLC and its design consultants for

specific application to the Union Bay Place development and site location. This report was prepared in

accordance with our proposal dated August 28, 2015, and signed on September 8, 2015. Within the

constraints of schedule and budget, we completed the work according to geotechnical practices

generally accepted for work done in the same or similar localities, related to the nature of the work we

accomplished, and done at the time our services were accomplished. We make no other warranty,

express or implied.

PROJECT UNDERSTANDING The project consists of a wood‐frame mid‐rise (up to five above‐grade stories) residential building with

one level of below‐grade parking. The project will occupy the entire footprint area of the site, which

will require a temporary (or perhaps permanent) shoring and/or underpinning system to support the

planned excavation for basement construction. At‐grade structures are adjacent to the site on the

north and south sides.

Subsurface conditions at the site are generally similar to those encountered throughout the adjacent

University Village area. The Burke Gilman Trail is an abandoned railroad grade in this area originally

constructed along what was then the north shore of Lake Washington. When the Montlake Cut was

constructed and the level of Lake Washington lowered by approximately nine feet, the area adjacent

to the railroad grade was filled and reclaimed. This reclaimed area extends from University Village

south to Husky Stadium. As a backwater slough, the area was occupied by deep peat deposits that

thinned from south to north. Fill materials were placed on top of the old slough deposits and a landfill

was developed to the south of and adjacent to NE 45th Street.

Groundwater in the area is high and generally close to the ground surface. In some areas artesian

groundwater conditions exist in the lower dense bearing soils because the area is adjacent to and at

the bottom of the surrounding hills. These conditions can be problematic for foundation construction.

Also, the loose nature of the fills and underlying soft/loose natural soils, coupled with high

groundwater, make the site susceptible to seismically induced liquefaction.

All the considerations above combine to make for complex foundation, shoring, and construction

dewatering issues. The site is designated an Environmentally Critical Area by the City of Seattle

Department of Planning and Development (DPD) in the categories of (1) proximity to an abandoned

landfill (within 1,000 feet), (2) liquefaction, and (3) peat‐settlement‐prone areas.

SUBSURFACE CONDITIONS Our understanding of the subsurface conditions at the Union Bay Place development site is based on

materials encountered in one soil boring advanced as part of this study, laboratory tests on selected

soil samples, logs of existing explorations and a geotechnical pre‐design report completed by others at

the site (Landau Associates 2015), available historical borings in the vicinity of the site, and our

experience on other development projects for University Village. Details of the conditions found at our

boring location are shown on the exploration logs in Appendix A. The results of geotechnical

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laboratory testing are in Appendix B. Exploration borings performed by others at the site, and other

historical borings in the vicinity, provided additional geotechnical data for this study and are in

Appendix C. Results of our slug testing are in Appendix D.

The subsurface information used for this study represents conditions at discrete locations across the

project site; actual conditions in other areas could vary. Furthermore, the nature and extent of any

variations may not become evident until additional explorations are performed or until construction

begins. If significant variations are observed at that time, we may need to modify our conclusions and

recommendations accordingly to reflect actual site conditions.

Soil Conditions Our understanding of the subsurface conditions is based on our new boring (HC‐101) and monitoring

wells (HC‐MW‐101 and HC‐MW‐102) completed as part of this study; existing explorations on or near

the site (borings B‐1, B‐2, B‐3, TB‐1‐77, TB‐2‐77 and TB‐3‐77); and our previous experience at other

nearby areas. Approximate locations of the soil explorations are illustrated on Figure 2, Site and

Exploration Plan. Cross‐section profiles of generalized subsurface conditions estimated from these

borings are presented on Figures 3 and 4.

The soil layers observed during the field explorations program were broadly categorized based on their

engineering properties into Engineering Soil Units (ESUs). In general, the soils observed in the

explorations consist of the following soil units, described in the order they were encountered from the

ground surface down:

ESU 1 – SILT, SAND, and GRAVEL (FILL). A relatively thick (up to approximately 25‐foot‐thick)

surficial layer of fill consisting of soft to stiff, sandy silt and very loose to medium dense gravelly,

silty Sand and sandy Gravel was observed at the ground surface or beneath the existing 3‐ to 5‐

inch‐thick paved areas.

ESU 2 – Very soft to soft, organic SILT and PEAT. The peat was encountered directly under the fill

in B‐1 from about 23 to 31 feet deep. The peat deposit is interbedded with occasional sand lenses.

This unit poses the greatest potential for settlement at the site. Foundation elements should not

bear in this soil unit.

ESU 3 – Medium dense to very dense, gravelly SAND. This unit was encountered directly below

the fill or peat, and is interpreted to be glacially overridden. It consists of various amounts of

slightly silty, gravelly to very gravelly SAND. This unit is suitable for foundation support. All the

borings terminate in this soil unit.

Groundwater Groundwater was encountered during drilling in the borings completed for this study. Groundwater

levels in the three on‐site monitoring wells were measured in February 2015 and October 2015. The

location of the monitoring wells is shown on Figure 2. Groundwater elevation (NAVD 88 datum) data

are presented in Table 1.


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Table 1 – Groundwater Elevations

Groundwater Location/Time Elevation at Monitoring Well

HC-MW-101 HC-MW-102 B-2 B-3

Ground surface 45 43 45 45

ATD 32 n/a 33 32.5

February 2015 n/a n/a n/a 39.3

October 5, 2015 32.0 23.4 n/a 36.8

ATD = At time of drilling (an approximate value)

All elevations in feet (NAVD 88 Datum)

Monitoring well in B-3 is screened within the aquifer below about elevation 15 feet; the rise of groundwater above

the ADT groundwater elevation indicates artesian conditions at depth, which is not representative of the near-

surface groundwater elevation.

The groundwater table is within the Fill unit at an elevation that ranges from about 23 to 32 feet.

Measured groundwater levels in HC‐MW‐101 and HC‐MW‐102 represent the groundwater within the

fill. Measured groundwater levels in B‐3 are influenced by artesian pressure in the lower dense bearing

soils. Groundwater elevations were highest at the east side of the site and lowest at the west side of

the site. Because groundwater level at the east side (Union Bay Place NE side) of the site is

approximately 8 to 9 feet higher than that at the west side, groundwater likely flows to the west.

During a site reconnaissance no seeps were noted on the slope along the west property line that

separates the subject site from the QFC site to the west.

Groundwater levels were obtained on the dates indicated on the logs, and are representative of the

time the readings were taken. Groundwater elevations vary depending on location, season,

precipitation, and other factors.

Hydraulic Conductivity (Slug Testing) Slug testing was conducted in wells HC‐MW‐101 and B‐3 on October 6, 2015, to determine the

hydraulic conductivity of the fill. We could not perform a slug test in well HC‐MW‐102 because of

insufficient water within the well. Slug tests are performed by rapidly inserting and removing a solid

PVC rod into a well and measuring the recovery of the groundwater levels. When the PVC rod is

inserted, it is a falling head test, and when the rod is removed, it is a rising head test. The water level

data generated from the tests were analyzed using the Bouwer and Rice method.

Average hydraulic conductivities determined from slug tests range from 6.2 x 10‐4 to 1.9 x 10‐3

centimeters per second (cm/sec) (1.8 to 5.4 feet/day). This range of hydraulic conductivity is

consistent with typical values for sand to silty sand. Slug test results are summarized in Appendix D.


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SEISMIC DESIGN RECOMMENDATIONS The site is in a seismically active area. In this section, we describe the seismic setting at the project site,

identify the seismic basis of design, provide the code‐based response spectrum parameters, and

discuss the seismic hazards at the site.

The seismicity of Western Washington is dominated by the Cascadia Subduction Zone, in which the

offshore Juan de Fuca Plate subducts beneath the continental North American Plate. Including the

subduction zone sources, three types of earthquakes are prevalent in Western Washington: interface

subduction, intraslab subduction, and crustal earthquakes.

Subduction Zone Sources. Subduction of the offshore Juan de Fuca Plate below the North American

Plate causes two distinct types of events. Large‐magnitude interface subduction earthquakes occur at

shallow depths near the Washington coast at the interface between the two plates; an example is the

1700 earthquake, which had magnitude of approximately 9.0. A deeper zone of seismicity is associated

with bending of the Juan de Fuca Plate below the Puget Sound Region; this bending produces intraslab

subduction earthquakes at depths of 40 to 70 kilometers (e.g., the 1949, 1965, and 2001 earthquakes).

Figure 5 depicts the Cascadia Subduction Zone and the various types of earthquakes it can produce.

Crustal Sources. Recent fault trenching and seismic records in the Puget Sound area indicate a distinct

shallow zone of crustal seismicity (e.g., Seattle and Tacoma Faults), which may have surficial

expressions and can extend 25 to 30 kilometers deep. Figure 6 shows the position of the Puget Sound

crustal faults in relation to the project site.

Site Class We determined the soil site class using information about the supporting foundation soil in

accordance with the 2012 International Building Code (IBC; International Code Council 2012). The soil

site class is based on the soil characteristic and a weighted average of the blow counts observed to a

depth of 100 feet below ground surface (bgs). For explorations advanced less than 100 feet bgs, we

assumed the material density below the deepest sample remains constant to 100 feet. Based on these

assumptions, seismic Site Class D would be assigned to the site. However, because the site contains

potentially liquefiable soil as discussed below, it is classified as Site Class F. The IBC and ASCE 7‐10

require a site‐specific analysis to determine seismic parameters for Site Class F soils if the period of the

structure is greater than 0.5 second. Based in the information provided by project structural engineer

(KPFF), we understand the period of the proposed building will not exceed 0.5 second. Therefore, in

accordance with ASCE 7‐10 (Section 21.3), the building can be designed to the code‐based Site Class D

spectrum.

Seismic Design Parameters We understand that the seismic performance is being evaluated according to IBC 2012 and ASCE 7‐10.

The basis of design for IBC 2012 is the risk‐targeted maximum considered earthquake (MCER), which

has a 2 percent probability of exceedance in 50 years, corresponding to a return period of 2,475 years.


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The basis of design for the 2012 IBC is two‐thirds of the hazard associated with the MCER. The IBC

event is referred to as the design event (DE).

The parameters were obtained from the USGS Seismic Design Maps web application

(http://earthquake.usgs.gov/designmaps/us/application.php; USGS 2008) and are shown in Table 2.

Table 2 – Seismic Design Parameters According to IBC 2012

Parameter Value

Latitude 47.6626° N

Longitude –122.2948° W

Site class E

Risk category III

Spectral response acceleration at short periods, SS 1.280 g

Spectral response acceleration at 1-second periods, S1 0.495 g

Site coefficient at short periods, Fa 1.0

Site coefficient at 1-second periods, Fv 1.505

MCER spectral acceleration at short periods, SMS 1.280 g

MCER spectral acceleration at 1-second periods, SM1 0.745 g

Design spectral acceleration at short periods, SDS 0.854 g

Design spectral acceleration at 1-second periods, SD1 0.497 g

Liquefaction Assessment Liquefaction is caused by a rapid increase in pore water pressure that reduces the effective stress

between soil particles, resulting in the sudden loss of shear strength in the soil. Granular soils that rely

on inter‐particle friction for strength are susceptible to liquefaction until the excess pore pressures can

dissipate. Sand boils and flows observed at the ground surface after an earthquake are the result of

excess pore pressures dissipating upward, carrying soil particles with the draining water. In general,

loose, saturated sandy soils with low silt and clay content are the most susceptible to liquefaction. Silty

soils with low plasticity are also susceptible to liquefaction under relatively higher levels of ground

shaking. For any soil type, the soil must be saturated for liquefaction to occur. Liquefaction can cause

ground surface settlement and lateral spreading.

We used empirical methods to estimate liquefaction potential based on the standard penetration test

(SPT) data obtained at the site. We used the SPT‐based liquefaction triggering procedure after Idriss

and Boulanger (2008). For our analysis of the MCE hazard levels we used an earthquake magnitude of

7.0 and a peak ground acceleration (PGA) of 0.512 g, which we obtained from USGS for the site

coordinates and Site Class D.

Our analysis shows that the loose fill soil below the groundwater table is susceptible to liquefaction.


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Post-Liquefaction Induced Vertical Settlement Post‐liquefaction settlement results from densification and redistribution of soils liquefied during

earthquake shaking. The ground surface typically settles unevenly across the area, which can result in

differential settlement of buildings.

We estimated liquefaction‐induced ground surface settlement using SPT corrections by Idriss and

Boulanger (2008) and volumetric strain formulations by Yoshimine et al. (2006). We calculated free‐

field ground surface settlements from the volumetric strains in contractive soils. We estimate that

approximately 2 to 4 inches of ground surface settlement could occur from an MCE event. Since this

settlement estimate does not include possible effects of sand boils and blowout resulting in the loss of

soil particles, actual liquefaction‐induced settlements may be even greater.

Surface Rupture The nearest mapped fault to the site is the North Trace of the Seattle Fault Zone, which lies

approximately 5.9 miles to the south. Based on the distance to the fault and the relatively long return

periods of earthquakes along the fault, we believe risk of surface fault rupture is low.

GEOTECHNICAL ENGINEERING DESIGN RECOMMENDATIONS This section of the report presents our conclusions and recommendations for the geotechnical aspects

of design and construction on the project site. We developed our recommendations based on our

current understanding of the project and the subsurface conditions encountered by our explorations.

If the nature or location of the development is different than we have assumed, we should be notified

so we can change or confirm our recommendations.

General Considerations Based on the current design plans and our discussions with the design team, the primary geotechnical

considerations for this project are:

Foundations. The peat layer that underlies the site is very compressible. Any loads applied at the

surface will consolidate the peat, which will result in surface settlement over time. In addition, the

limited liquefaction‐induced subsidence will result in unacceptable levels of post‐construction

settlement if shallow foundations are used. Wew recommend supporting the structure loads

using augercast piles or drilled shafts.

Temporary Shoring. The project includes one level of below‐grade parking, which will require

temporary (and possibly permanent) structural shoring of the planned excavation. The shoring will

need to support existing at‐grade structures adjacent to the north and south sides of the site as

well as the city right‐of‐way along Union. A cantilevered soldier pile wall, with the use of a soldier

pile wall with one row of tieback where needed, is anticipated to provide a suitable option for

temporary shoring. The temporary shoring along the north property line may consist of


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underpinning of the existing building or could be placed just to the south of the building such that

the building will act as a surcharge on the shoring system. It is also possible that the shoring

system could be used for vertical support of the new building.

Groundwater Control. Groundwater in the area is high and close to the anticipated basement slab

level. To accommodate the proposed finish floor elevation, temporary dewatering will be needed

and a permanent drainage layer will need to be installed. Alternatively, it may be appropriate to

construct the lower portion of the lower level of the building to be “water tight”.

Site Preparation For site preparation, the asphalt pavements, concrete walkways, sidewalks, and landscape vegetation

should be removed, and existing structures on the site should be demolished. Removed asphalt, brick,

concrete, or topsoil should not be reused as structural fill.

It will likely be necessary to relocate or abandon some or all utilities. Excavation of these utility lines

will occur through fill materials. Abandoned underground utilities should be removed or completely

grouted. Ends of remaining abandoned utility lines should be sealed to prevent soil or water from

entering the pipe. Soft or loose backfill materials should be removed, and excavations should be

backfilled with structural fill.

Foundation Considerations Given the significant depth of compressible and liquefiable soils (25 to 40 feet, based on the existing

borings at the site), some form of deep foundation system will be required to support the proposed

structure. Typical pile types would be driven steel, augercast, drilled shafts, micropiles, or helical steel.

All these have been used in the area and the choice depends on cost and the specific project

conditions.

Driven piles are likely NOT a good choice for this site, as the vibrations associated with either impact or

vibratory pile driving could affect the adjacent buildings.

Helical piles are literally screwed into the ground using high‐powered torque equipment. These piles

were used successfully at the South Building at University Village, which is adjacent to the settlement‐

sensitive 45th Street Viaduct. Capacities of about 250 tons can be easily achieved. The downsides are

that the equipment is not locally available and costs can be higher than would be practical.

Augercast piles are readily available locally and are low cost in terms of dollars per foot of length per

ton of capacity, under normal circumstances. Their installation does not cause excessive vibrations.

The risk with augercast piles is the potential for the foundation soils to heave due to artesian

conditions at depth. The other cost factor for augercast piles at this site is the potential cost of

disposing of the spoils from the pile holes. If the spoils are contaminated, the disposal cost can

increase the effective unit cost of the piles.


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Small diameter drilled shafts may be an alternative for this site. Based on discussions with the design

team it may be appropriate to use drilled shafts that are the same diameter as the proposed soldier

piles for the shoring system. Micropiles may be an alternative to augercast piles or drilled shafts. The

downside of micropiles is that they cannot develop substantial lateral capacity, so the structure would

need to be designed to accommodate lateral force demands at the subgrade perimeter walls.

An alternative to pile foundations for this site is ground improvement that would prevent liquefaction

and allow for support of the building on shallow foundations. Typical ground improvement methods

include stone columns and rammed aggregate piers. Stone columns are constructed by vibrating a

pipe into the ground and then placing rock through the bottom end of the pipe as the pipe is

withdrawn. The vibration has the effect of partially densifying the ground and the column of stone

adds strength to the ground such that shallow footings and slabs‐on‐grade can be used to support the

building loads. Stone column ground improvement was successfully used for construction of the

parking garage to the north of the existing QFC store

Rammed aggregate piers are somewhat similar to stone columns. They are constructed by driving a

steel pipe to the desired depth and then placing rock through the pipe. A downhole rammer is then

used to tamp the rock as the pipe is withdrawn. The process relies more on this ramming process to

compact the rock than does the stone column process, which relies more heavily on vibration to

densify the rock

The risk associated with both these methods of ground improvement is the potential for adverse

impacts to the adjacent structures due to vibrations during installation. The risks and cost benefits

associated with all these alternatives need to be evaluated by the entire project ream (especially

including the contractor) to arrive at the best solution. At this point we are not addressing these

ground improvement methods

Adjacent Structures Buildings are adjacent to the site on the northern and southern property lines. Available information

indicates that the one‐story commercial building to the north bears on near‐grade shallow footings.

The temporary shoring will need to support these shallow footings as well as supporting the new

construction. The Safeway building to the south is pile‐supported. Available plans from the time the

Safeway building was constructed indicate ground surface is about 6 to 8 feet beneath the building’s

finished floor elevation; therefore, the bottom of the pile may be that far below floor elevation.

On the northeast side of the Safeway store (along the loading dock area) a short wall retains soil from

the project site. This retaining wall appears to be pile‐supported and includes battered timber piles

that may extend into the project site (depending on the depth of the piles).

Augercast Pile Foundations Because of the weak near‐surface soil at the site, we believe augercast piles may provide a cost‐

effective option to support the building loads. We anticipate that 16‐ to 24‐inch‐diameter piles may be

used. This size and type of pile foundation can likely provide the necessary support for structural loads,


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assuming proper design and installation. We will work with the project team to assess and provide

design recommendations for other foundation support options if augercast piles are found to be

problematic considering the artesian conditions at depth described above.

Vertical Pile Capacity

Vertical compressive loads can be resisted by friction along the pile sides and by end‐bearing at the tip.

Vertical uplift loads are resisted by friction alone. Column design loads are unknown at this time.

We recommend embedding the piles at least 15 feet into the medium dense to very dense, gravelly

SAND (ESU 3) to develop the full allowable axial capacities recommended in Table 3. Capacities are

generally based on the soil profile at B‐1 where peat was identified. Approximate bearing elevation

contours are shown on Figure 2. With a base of structural slab at approximately elevation 32 feet,

these piles are expected to be about 35 feet long, corresponding to a tip elevation of about –3 feet (i.e.

tipped about 46 feet below existing ground surface).

Table 3 – Allowable Axial Capacity for Augercast Piles

Pile Diameter

in inches

Allowable

Compression

Capacity in kips

Allowable

Tension

Capacity in kips

16 83 60

18 105 72

24 187 96

30 234 120

The allowable capacities provided incorporate the effects of downdrag loads resulting from

compression of the soft peat and liquefaction‐induced settlement in the sand layers. We estimated the

downdrag force using a depth to dense bearing soil of 31 feet, and a downdrag adhesion of 250

pounds per square foot (psf) around the perimeter of the pile. Based on this, the downdrag loads are

estimated to be 32, 41, 49, and 61 kips for 16‐, 18‐, 24‐ and 30‐inch‐diameter piles, respectively. The

allowable axial compressive capacities in Table 3 include a reduction equal to the downdrag loads

expected from the peat and liquefiable soils.

The pile capacities are based on a factor of safety of 2.0 or greater for compressive and uplift loading.

If piles are spaced greater than three pile diameters measured center‐to‐center, it will not be

necessary to reduce the allowable compression capacities of individual piles in a pile group.

Higher capacities than those recommended above could be realized by conducting a full‐scale pile load

test program to measure the load/deflection behavior of the augercast pile of the proposed size.

Estimated Pile Settlement. Assuming properly installed augercast piles, we estimate total settlement

will range from 1/4 to 1 inch. Differential settlement between adjacent pile‐supported columns should


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be less than about one‐half of the total settlement. The pile settlement associated with the design

loads should occur within the first few days after loading. Any future additional settlement would likely

result from downdrag forces caused by settlement of the peat layer or during and after liquefaction

under earthquake shaking. This condition may result in some additional settlement of the pile

foundation as additional end‐bearing capacity is mobilized by downdrag forces.

Lateral Pile Capacity

Lateral loads, which may be imposed on the piles by wind or earthquake forces, can be resisted by

horizontal bearing support of near‐surface soil adjacent to the piles. The lateral resistance of a drilled

shaft depends on its length, stiffness in the direction of loading, proximity to other shafts, and degree

of fixity at the head, as well as on the engineering properties of the soil. The computer program LPILE

is often used to calculate lateral load capacity and deflection for the drilled shaft. LPILE uses lateral soil

reaction (p) and lateral deflection (y) curves generalized from field load tests, along with soil input

properties, to approximate lateral pile deflections and moments for piles subjected to an axial load.

We recommend using the LPILE soil input parameters in Table 4 for augercast piles. Our soil profile

was primarily based on B‐1 on the west side of the site.

Table 4 – Soil Parameters for LPILE Input (B-1)

Soil Layer

Description

Layer

Depth in

feet

Layer

Elevation

in feet

Effective

Unit

Weight

in pcf

Soil

Model

Friction

Angle in

degrees

Slope of

Soil

Modulus

(k) in pci

Fill 0 to 11 43 to 32 125 API

SAND 30 43

Fill –

submerged 11 to 23 32 to 20 62.6

API

SAND 30 32

Peat 23 to 31 20 to 12 4.6 API

SAND 9 5

Glacial soil

(till/outwash) below 31 below 12 72.6

API

SAND 38 125

For full lateral capacity, we recommend spacing piles at least 6D center‐to‐center. Shafts spaced

closer than 6D should be adjusted for group effects according to Table 5. Interpolation should be used

for spacing values other than 3D and 5D.


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Table 5 – Pile P-multipliers from AASHTO (2014)

Pile

Spacing

AASHTO 2014 Reduction Factors (p-multipliers)

1st Row 2nd Row 3rd and greater Rows

3D 0.8 0.4 0.3

5D 1.0 0.85 0.7

Liquefaction Effects. Likewise, p‐multipliers can be used in analysis to account for the reduced

stiffness caused by liquefied soils. For the liquefied condition, LPILE analysis was performed using p‐

multipliers according to guidelines in the 2014 Washington State Department of Transportation

(WSDOT) guidelines. P‐multipliers for liquefied soil and group effects are not applied simultaneously in

accordance with those guidelines.

A p‐multiplier of 0.2 should be applied along the length of the liquefied zone only (Fill – submerged).

Passive Pressure on Pile Caps and Grade Beams

Soil adjacent to pile caps and grade beams can passively resist structure movement. We recommend

the following for calculating the passive soil resistance:

Neglect the upper 18 inches of soil below the structural slabs because of expected settlement of

the subgrade soils.

Neglect passive resistance below elevation 21 feet, which corresponds to approximately the

highest elevation of observed peat.

Use an allowable passive equivalent fluid weight of 115 pounds per cubic foot (pcf). This value

assumes soil is below the groundwater table and includes a factor of safety of 1.5.

Augercast Pile Installation

We recommend that a Hart Crowser representative observe the augercast pile installation to evaluate

the contractor’s operation and collect and interpret the installation data. As the completed pile will be

below the ground surface and cannot be observed during construction, judgment and experience must

be used to determine whether it is acceptable. This also requires use of an augercast pile contractor

who is familiar with such installations. We recommend close monitoring of installation procedures,

such as installation sequence, auger withdrawal rate, grouting pressure, and quantity of grout used

per pile. Variations from the established pattern, such as low grout pressure or excessive settlement of

grout in a completed pile, would make the pile susceptible to rejection.

We recommend the following for augercast pile installation:

To prevent interconnection of grout between piles, do not install two piles within five pile

diameters of each other in a single 24‐hour period. At the time of construction, evaluate whether

this period may need to be increased because of the very soft peat layer.


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Require the contractor to provide a pressure gauge in the grout line.

Minimum pressures should be those required to maintain a steady flow of grout to the auger. A

typical value of 100 pounds per square inch (psi) should be used for this purpose.

Rapid drops in the grout pressure of 50 psi or more occurring when otherwise accepted

procedures are used should be specified as a possible cause for reconstructing the pile.

Grout injection and auger withdrawal from the soils should be done at rates that allow

maintenance of a positive grout head of at least 10 feet above the bottom of the auger. A larger

head may be required to counteract the high groundwater table and water pressure at the site.

Withdraw auger from hole at a slow rate so that pressure on the grout column is maintained.

Require contractor to provide a way to monitor quantity of grout used per pile. A stroke counter

on the group pump is the most efficient means to determine grout quantity.

Require the contractor to rotate the auger after initial grout pumping (of about 2 cubic feet)

before beginning to withdraw the auger.

Require the contractor to install a full length rebar (aka center bar) down the pile center when

grouting is completed, to ensure a properly constructed pile.

Augercast piles will generate soil spoils that will likely need to be disposed of off site. Any

environmental considerations that affect disposal of the spoils should be identified before

construction.

Drilled Shaft Capacity For preliminary drilled shaft design we assumed that 2‐ or 3‐foot‐diameter drilled shafts will be

sufficient for axial and lateral foundation support of the sterile corridor. The compressive capacity of

drilled shaft foundations is achieved through a combination of end‐bearing support at the pile tip and

side friction between the pile material and the soil along the embedded pile length.

We recommend using the allowable design capacity provided in Table 3 for drilled shafts.

Drilled Shaft Installation The contractor should review our recommendations and be prepared to address the construction

considerations below. If significant variations are observed at any time, we may need to modify our

conclusions and recommendations. For drilled shaft installation, we recommend:

Be aware that drilled shafts will produce a large volume of drill cuttings that may be contaminated

and require chemical analysis; soil will likely require off‐site disposal.

Have the contractor review the boring logs thoroughly and choose appropriate drilling methods.


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Have the contractor clean slough and other loose material from the bottom of all drilled shafts

before placing concrete.

Tremie the concrete from the bottom of the shaft if groundwater is encountered or if drilling mud

is used to maintain an open hole.

Although cobbles and/or boulders were not encountered in explorations near the proposed drilled

shaft locations, based on the local geology, the contractor should be prepared to deal with large

obstructions that may be encountered during excavation.

Clean out the shaft toe no more than 6 hours before placing concrete so suspended solids do not

have much time to settle to the toe and reduce its geotechnical stiffness.

Where multiple drilled shafts are planned within 5 diameters of each other, consider the timing of

excavation and concrete placement of the adjacent shafts. Provide the adjacent drilled shaft with

adequate cure time before starting to excavate the next drilled shaft. This will not only minimize

the potential for communication between adjacent shafts but will also reduce the likelihood of

disturbing the set and cure of the concrete in the recently poured shaft.

We recommend having a representative from Hart Crowser on site full time for special inspection

of drilled shaft installation. The on‐site geotechnical representative should verify that soil

conditions encountered during drilled shaft excavation match those assumed during design before

concrete is placed. The geotechnical representative should also verify that the shaft is installed

according to the project plans and specifications.

Temporary Shoring A shoring system will be required to provide temporary lateral support for safety and stability of the

adjacent structures to the north and south of the proposed building, as well as for the right of way on

the west side of the site. Based on the soil and groundwater conditions, it is our opinion that

excavations could be supported using a combination of conventional soldier piles with tieback anchors

and cantilevered soldier pile wall.

Shoring should be designed by a professional structural engineer registered in the State of

Washington. We also recommend that we review the geotechnical aspects of the shoring design

before construction. It is generally not the purpose of this report to provide specific criteria for the

contractor’s construction means and methods. It should be the responsibility of the shoring

contractor to verify actual ground conditions and determine the construction methods and procedures

needed to install an appropriate shoring system.

Lateral Earth Pressure

Lateral earth pressures for the design of the soldier pile wall depend on the type of wall and its ability

to deform. The wall may be designed using active earth pressure if the top of the wall is allowed to


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deform about 0.001 to 0.002 times the wall height and if no settlement‐sensitive structures or utilities

are within the deformation zone.

At‐rest earth pressure should be used to design the wall if settlement‐sensitive structures or utilities

exist within the potential deformation zone, or where the wall system is too stiff to allow sufficient

lateral movement to develop an active condition. We recommend the following:

Use lateral earth pressures on Figure 7.

If construction or vehicular traffic will be present above the wall, within a distance from the wall

face equal to the wall height, include a 2‐foot surcharge in the design, as shown on Figure 7.

Additional surcharge loads (e.g., adjacent footing loads, material stockpiles, or other large loads)

should be computed using the methods shown on Figure 9. These additional loads should be

added to those calculated for the shoring wall based on Figure 7.

The lateral earth pressures presented herein are based on dewatered conditions, with the

understanding that hydrostatic pressure does not act on the walls.

Soldier Pile Design

Soldier piles must be embedded deeply enough to provide kick‐out resistance for the portion of the

wall below the lowest support. Soldier piles must be designed to carry the bending stresses from the

lateral earth pressure against the pile and the lagging between soldier plies. We also recommend the

following:

Design soldier piles to bear in the medium dense to very dense gravelly Sand layer (ESU 3).

Use end‐bearing and skin friction design values presented on Figure 7.

Embed piles at least 10 feet below the bottom of the excavation after allowing 2 feet for

disturbance.

Design soldier piles for bending using a uniform loading equivalent to 80 percent of the design

values and analyze for shear using total load.

For design against kickout, compute the lateral resistance on the basis of the passive pressure

presented on Figure 7, acting over three times the diameter of the concreted soldier pile section

or the pile spacing, whichever is less.

The above recommendations are based on proper installation of the soldier piles as described below.

Soldier Pile Installation

Conditions such as caving soil and groundwater can loosen soils at the bottom of the soldier pile

excavation and reduce bearing capacity of the zone of disturbed soils. We recommend that a Hart


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Crowser representative monitor soldier pile installations so that construction methods can be adjusted

in a timely manner, if needed.

We recommend the following for soldier pile installation:

Require that the contractor to be prepared to case the soldier pile installations. The actual

necessity of casing should be determined in the field at the time of installation.

Prohibit the use of drilling mud unless reviewed and approved by the geotechnical and structural

engineer.

Place concrete in soldier pile holes with a tremie pipe. Hart Crowser must verify the integrity of the

soil at the base of the hole before concrete is placed.

Lagging

Loss of ground between the soldier piles is prevented using lagging. Lagging typically consists of timber

planks or concrete panels. We recommend using the thickness (rough‐cut) of temporary lagging

provided in Federal Highway Administration (FHWA) Geotechnical Engineering Circular No. 4, “Ground

Anchors and Anchor Systems,” based on “Competent Soils” and the selected clear span of soldier piles.

For clear spans of 5 feet or less, the recommended lagging thickness is 2 inches. For clear spans

between 5 and 8 feet, the recommended lagging thickness is 3 inches.

Prompt and careful installation of lagging, particularly in areas of seepage and loose soils, is important

for maintaining the integrity of the excavation. Proper installation should be the responsibility of the

wall contractor so that soil failure, sloughing, and ground loss are prevented, and so that safe working

conditions are provided.

Soldier pile wall construction may be difficult if cobbles, boulders, or loose sands and gravels are

encountered in the excavation. If these conditions are encountered, substantial raveling of the soil

could occur. The contractor should be prepared to place lagging in small vertical increments in areas of

utility backfill or caving soil, and should be prepared to backfill voids behind the wall that may result

from ground loss during construction.

We recommend the following for lagging:

Backfill voids greater than 1 inch using sand, pea gravel, or a porous slurry. Backfill the void spaces

progressively as the excavation deepens. The backfill must not allow potential hydrostatic

pressure buildup behind the wall. Drainage behind the wall must be maintained. If not, hydrostatic

water pressure should be added to the recommended lateral earth pressures.

Install extra lagging above the shoring wall if there is a slope above the wall, to provide a partial

barrier for material that could ravel down from the slope face and fall into the excavation.


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Tieback Anchor Design and Construction

We expect that tieback anchors can be used for external lateral support of the soldier pile walls. We

recommend the following for tieback anchor design:

Locate anchor portions of the tiebacks below the no‐load zone shown on Figure 7.

For planning, use allowable adhesion values presented on Figure 7, which are appropriate for

pressure‐grouted anchors. The shoring contractor must choose appropriate means and methods

to achieve the design adhesion based on their experience on similar sites.

Locate anchors at least three tieback diameters apart.

Pump structural grout into the anchor zone using a grout hose or tremie hose placed at the

bottom of the anchor.

Install a bond breaker such as plastic sheathing or a PVC pipe around the tie rods within the no‐

load zone.

Grout and backfill tiebacks immediately after placing the anchor. To prevent collapse of the holes,

ground loss, and surface subsidence, do not leave anchor holes open overnight.

Take care not to mine out large cavities in granular soil.

Maintain continuous cutting return if using pneumatic drilling techniques so that air pressure is

not channeled to nearby utility vaults, corridors, or subgrade slabs, because air pressure may

damage such structures.

Design anchor lengths so that they do not conflict with any underground utilities and/or support

elements of the adjacent structures.

Identify existing facilities adjacent to the project site including buried utilities and foundations, as

these may affect the location and length of the anchors.

Select the tieback anchor material and the installation technique. The selected installation method

must be subject to field verification with performance and proof‐testing, as discussed in

Attachment 1.

Install anchors to minimize ground loss and do not disturb previously installed anchors. During

tieback drilling, wet or saturated zones will be encountered, and caving or blow‐in could occur.

Drilling with a casing may reduce the potential for these conditions and ground loss.

Hart Crowser should review the design for anchor locations, capacities, and related criteria prior to

implementation.


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The anchor design values recommended on Figure 7 include a factor of safety of at least 2.0. This

factor of safety provides for a reasonable additional load capacity in case an unforeseen increase in

unit soil load develops because of irregularities that can occur during installation of the anchor. The

variable soil conditions and unit friction values mean that some field changes in anchor length may be

necessary. For planning, we recommend designing anchors according to the above criteria.

Tieback Anchor Testing

The tiebacks will be tested to confirm the appropriateness of the anchor design values and to verify

that a suitable installation is achieved. The procedure for performance and proof‐testing is presented

in Attachment 1 and summarized below. For testing of tieback anchors, we recommend:

Require the shoring contractor to complete two successful 200 percent performance tests on one

tieback. Contract documents should be prepared such that additional verification tests could be

performed on a unit price basis if different site conditions are encountered.

For anchors installed for the 200 percent verification test, the specifications should include

components to prevent friction contribution between the grout column and the soil in the no‐load

zone.

Proof‐load each production anchor to 133 percent of the design load to test for total movement

and creep.

Permanent Subgrade Building Walls

Lateral Earth Pressures for Walls Constructed Against Temporary Shoring

Permanent walls constructed flush with temporary shoring systems may be designed for the same

active (or at‐rest) earth pressures used in the design of the shoring system (Figure 7).

Seismic Earth Pressure

The lateral earth pressures for permanent walls must include a seismic earth pressure increment. This

additional lateral earth pressure can be approximated as a rectangular uniform pressure of 7H for a

yielding wall. Apply the seismic earth pressure from the top of the wall to the bottom of the

excavation, a height that is defined as the height (H) of the wall as it is dimensioned and shown on

Figure 8. This increment is calculated using the IBC hazard level for the site location.

Additional Surcharge Pressures

We recommend applying a surcharge of 250 psf to the top of the proposed excavation for

computations to provide some allowance for possible surface pressures near the excavation such as

light vehicles or small material stockpiles. Surcharge pressures resulting from heavier loads such as

buildings, footings, heavy equipment, or large material stockpiles should be calculated using Figure 9.

These additional loads would be added to the soil pressure calculated for permanent foundation walls.


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Hydrostatic Groundwater Pressure

For walls that are not drained, add a triangular lateral hydrostatic pressure of 62.4HGW psf, where HGW

is the depth of structure below the groundwater table. We recommend using a design groundwater

table elevation of 32 feet.

This recommendation presumes that drainage will be installed above the groundwater table to

prevent buildup of water pressure caused by perched water and precipitation. Walls without drainage

must be designed for full horizontal hydrostatic pressure as well as hydrostatic uplift forces on the

bottom of the slab‐on‐grade. Additionally, the waterproofing system would need to be designed and

installed by others to facilitate a functioning, dry lowest level.

Wall Drainage

To reduce the risk of potential hydrostatic pressure buildup, we recommend placing a dimpled

geotextile drainage geocomposite (e.g., TenCate Mirafi G‐Series) between the soil and the building

wall. Alternatively, free‐draining granular material (less than 3 percent passing the US No. 200 sieve)

could be used as structural fill within an 18‐inch‐wide zone immediately behind the wall. This curtain

drain should be continuous and hydraulically connected to a footing drain collection system at the

base of the wall, as described in the Permanent Drainage section.

Floor Slabs We recommend using structural floor slabs supported on pile caps. Considering the poor soil

conditions, the soil beneath the slab will settle over the life of the building, creating a void below the

slab. The structural slab should be designed assuming no soil support. Permanent drainage below the

slab should be installed as described in the Permanent Drainage section.

Construction Dewatering We anticipate an excavation to bottom of foundations of around 10 to 12 feet or more. This would

place the bottom of excavation at or 1 to 2 feet below the static groundwater table. This is a significant

depth below the groundwater table. Construction dewatering could likely be easily completed using

construction dewatering wells or a well point system. If there are no contaminants or if their

concentrations are low enough, the water could be disposed of in the sanitary system. Construction

dewatering will need to be carefully assessed, as the groundwater table will be lowered not only at the

Union Bay Place site but at the adjacent sites.

Construction Dewatering Recommendations

The groundwater table is relatively shallow; therefore, we anticipate the groundwater table will be

encountered during construction. Construction dewatering is required when excavating below the

groundwater table to maintain dry and stable working conditions in the bottom of the excavation.

Typically, contractors prefer to have the groundwater table lowered a foot or two below the bottom of

excavations. At the project site, this equates to temporarily lowering the groundwater to about

elevation 32 feet, which coincides with the design groundwater elevation. We recommend the

following for dewatering during construction:


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Temporary construction dewatering will be required when excavations are below the

groundwater table. The actual dewatering methods and schedule will be selected by the

construction contractor, with our review. In our opinion, dewatering will require using a

combination of sump and/or vacuum well point systems around the excavation. Dewatering will

need to be continuous during construction below the groundwater table.

We recommend lowering the groundwater table by no more than 2 feet below the bottom of

excavation to maintain stable working conditions in the bottom of the excavation while minimizing

off‐site settlement. This could be reduced to 1 foot during construction, if necessary.

The contractor should use a qualified licensed hydrogeologist to design the dewatering system.

The general contractor should retain an experienced dewatering contractor to install and operate

the dewatering system. Hart Crowser should review the dewatering plan before it is implemented.

Steady‐state dewatering rates will vary depending on the excavation size and depth, dewatering

method, schedule, and soil conditions. Generally, beginning dewatering one to two weeks before

construction is recommended to allow sufficient time to reach design water levels. Initial

dewatering rates can be much higher until a stabilized water level is achieved.

We recommend disposing of dewatering discharges by a local storm drain. Disposal of dewatering

discharges by infiltration or recharge will likely be impractical because of the relatively shallow

groundwater table.

Our services were provided to help assess temporary dewatering for the planned excavation, shoring,

and construction of new utilities that will be, in part, beneath the groundwater table. Our estimate of

dewatering discharge rates is based on our evaluation of how dewatering operations may be

implemented at the site, considering conditions described in the geotechnical studies. The actual

dewatering rates will depend on the dewatering methods and schedule selected by the contractor.

Site‐specific information is limited to exploration borings and in situ hydraulic testing completed at

widely spaced locations; therefore, conditions may differ from those assumed.

Geotechnical Impacts of Dewatering

Geotechnical impacts of dewatering are primarily related to dewatering‐induced settlement. We

estimated the settlement that could result from lowering the groundwater table at the site. Given the

soft and compressible nature of the soils underlying the site, lowering the groundwater table will

increase the overburden stress on these compressible soils, which could result in unwanted and

excessive settlement of the adjacent buildings.

The Safeway building to the south is on pile foundations and would not be susceptible to settlement.

The building to the north is on shallow footings and could be significantly affected by settlement from

dewatering. The amount of settlement that occurs depends on the soil conditions, as well as on the

amount and duration of dewatering. Once the dewatering plan is known, we should be notified so we

can assess settlement that may occur during construction.


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Waterproofing

If waterproofing is required below grade, a specialty waterproofing subconsultant should be retained

to design it. We have seen waterproofing systems such as a heavy plastic membrane liners, bentonite

clay panels (i.e., Volclay or equivalent), and other interior or exterior sealants used effectively on

projects similar to this one.

Permanent Drainage We make the following comments and recommendations related to the permanent drainage system:

Use a drainage layer below the slab consisting of 4 inches of clean sandy 1‐inch‐minus gravel and

containing less than 30 percent passing the US No. 4 Sieve and less than 3 percent fines (i.e.,

material passing the No. 200 US sieve) based on the minus 3/4‐inch fraction.

Place dimpled geotextile drainage geocomposite (e.g., TenCate Mirafi G‐Series) between the

structural slab and the granular drainage layer. Cut holes in the membrane portion of this layer at

vent locations to allow upward flow of methane gas.

Install perimeter cross drains in the granular drainage layer consisting of 4‐inch‐diameter

perforated drain pipe spaced no more than 25 feet on center in 9‐inch‐thick drain trenches.

Locate the drain pipe a minimum of 3 inches below the base of the structural slab.

Slope pipe to drain at a minimum 0.5 percent. This slope requirement may require stacked drain

pipes. The lower drain pipe should be a tight line (i.e., not perforated).

Locate pipe perforations on the top half of the pipe.

Use a separation geotextile fabric (e.g., TenCate Mirafi N‐Series) between the native soil and the

drainage layer.

Dispose of drainage system water into a local storm drain. Site infiltration or recharge is

impractical because of the shallow groundwater table.

Structural Fill We anticipate that structural fill will be required for backfilling behind walls, for backfilling of utility

trenches and other miscellaneous excavations, and possibly for replacement of overexcavated, soft, or

wet soils. We recommend the following regarding placement of structural fill:

Place structural fill in maximum 10‐inch‐thick loose lifts and compact it to a firm condition to

support concrete placement as observed and verified by a Hart Crowser field representative.

The moisture content of the fill should be controlled within 2 percent of the optimum moisture.

Optimum moisture is the moisture content corresponding to the maximum Proctor dry density.


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If a select soil will be imported for use as structural fill, we recommend using a clean, well‐graded

sand or sand and gravel with less than 5 percent by weight passing the No. 200 mesh sieve (based

on the minus 3/4‐inch fraction). If imported soil is used during wet weather periods, we

recommend a gravel content (material coarser than a US No. 4 sieve) of at least 30 percent.

If small, hand‐operated compaction equipment is used to compact structural backfill, fill lifts

should not exceed 8 inches of loose thickness.

Any import material to be used as structural fill should be sampled from the supplier’s pit before

delivery or use on site, to determine the maximum dry density, gradation, and optimum moisture

content.

Use of On‐Site Soils as Structural Fill

The suitability of excavated site soils for structural fill will depend on the gradation and moisture

content of the soil when it is placed. As the amount of fines (that portion passing the No. 200 sieve)

increases, the soil becomes increasingly sensitive to small changes in moisture content, and adequate

compaction becomes more difficult to achieve. Soil containing more than about 5 percent fines cannot

be consistently compacted to a dense non‐yielding condition when the water content is greater than

about 2 percent above or below optimum.

Drilling of augercast piles for structures in this area will generate cuttings of a variety of soil types. Peat

cuttings are unsuitable for reuse as fill. We also recommend against using the underlying granular soil

cuttings because of difficult segregation from unsuitable soils, and intermixed and wet conditions. In

general the site soils are not well suited for reuse as structural fill.

Temporary Open Cuts The stability and safety of cut slopes depend on a number of factors, including:

The type and density of the soil;

The presence and amount of any seepage;

The depth of cut;

The proximity of the cut to any surcharge loads near the top of the cut (such as stockpiled

material, traffic, or structures) and the magnitude of these surcharges;

The duration of the open excavation; and

The care and methods used by the contractor.

Temporary soil cuts for site excavations that are more than 4 feet deep should be adequately sloped

back to prevent sloughing and collapse in accordance with Washington Department of Occupational

Safety and Health (DOSH) guidelines (WAC Chapter 296‐155 Part N). Based on these guidelines, the fill

and native subsurface materials at the site would be classified as Type C. We recommend the following

for open cuts:

Use a maximum allowable slope for excavations less than 20 feet deep of 1.5H:1V.


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Do not excavate below the bearing elevation of the existing footings or structural elements.

Consult with the geotechnical engineer during construction to limit the size of these excavations

and the amount of time they remain open.

Protect the slope from erosion by using plastic sheeting, especially during wet weather excavation.

Limit the maximum duration of the open excavation to the shortest time possible.

Place no surcharge loads (equipment, materials) within 10 feet of the top of the slope, in general.

However, more or less stringent requirements may apply depending on field conditions and actual

surcharge loads.

Use special care when excavating through the soft peat layer.

Because of the variables involved, actual slope angles required for stability in temporary cut areas can

be only estimated (not determined precisely) before construction. We recommend that stability of the

temporary slopes used for construction be the sole responsibility of the contractor, since the

contractor is in control of the construction operation and is continuously at the site to observe the

nature and condition of the subsurface. All excavations should be made in accordance with all local,

state, and federal safety requirements.

Utilities Utility trench cut design should generally be the responsibility of the contractor. For shallow trench

excavations (less than 4 feet in depth), open cutting may be used. Use of temporary shoring may be

necessary if deeper excavations are required for placement of utilities. The contractor should verify

the conditions of the side slopes during construction and layback trench cuts as necessary to conform

to current standards of practice.

The minimum dry densities recommended below are a percentage of the modified Proctor maximum

dry density as determined by the ASTM D1557 test procedure. Our recommendations for bedding and

trench backfill materials are:

At least 4 inches of bedding is recommended for all pipe utilities. Bedding materials should consist

of well‐graded sand and gravel with less than 3 percent material passing the No. 200 sieve (based

on the minus 3/4‐inch fraction). Bedding material should be compacted to a firm non‐yielding

condition.

The recommended bedding backfill materials can be used as backfill around the pipe utilities (pipe

zone backfill). Pipe zone backfill should extend to at least the top of the pipe utility.

For bedding material beneath catch basins and manholes, we recommend 6 inches of imported

structural fill (or acceptable on‐site material) that consists of well‐graded sand and gravel with less

than 3 percent material passing the No. 200 sieve (based on the minus 3/4‐inch fraction). The

bedding material should be compacted to 90 percent.

Utilities that extend below the groundwater table should be evaluated for the potential to float

out of the ground at the high groundwater level.


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Deeper utilities may require dewatering well points to obtain a suitable working base. The

contractor may elect to place a geotextile fabric at the base of the excavation to help create a

suitable working surface.

Utilities should be designed for significant settlement between those pile‐supported and those

supported on‐grade.

Utilities Below the Building. Settlement is expected to occur over time below the building. Utilities

that gravity flow should be designed to hang from the structural slab so that the elevation remains

unchanged under the building. The connection between these hanging utilities and those on grade

must be designed for significant differential settlement. For pipe bedding and backfill around hanging

utilities, we recommend using pea gravel. As subgrade settles over time, the pea gravel will have the

ability to flow around the pipe and avoid a downdrag load that could possibly damage the pipe.

Utility Vaults. We recommend designing utility vaults to resist both the compressive load of the vault

on the subgrade and the hydrostatic uplift force of the groundwater table acting on the base of the

vault (i.e., design to preclude the vault from floating out of the ground when empty). Depending on

space requirements, excavation for utility vaults may require temporary shoring.

Methane Venting The site is within a Critical Area as mapped by the City of Seattle because it is within 1,000 feet of a

historical landfill (i.e., the Montlake Landfill that was across NE 45th Street). This landfill was closed in

1971. In addition to gases generated at the landfill, however, gases can be generated by organic

decomposition of the peat. Based on the distance from the landfill and subsurface conditions, there is

potential for migration of gas (primarily methane) to the site. Therefore, we recommend the following

mitigation measures to protect against migration of methane or methane released from the peat soil

underlying the site.

We recommend installing a passive venting system beneath the building to protect against excessive

methane gas buildup. This system works because methane gas is lighter than air and tends to migrate

upward. The passive venting system consists of vertical vent risers and concrete treatment.

We recommend the following for vent risers:

Connect vent risers to allow upward air/gas flow from the granular drainage layer at the base of

the structural slab.

Install six vent risers at locations around the building perimeter.

Locate and connect vent risers such that all areas below the structural slab can be vented.

Use cast iron vent risers that have a minimum inside diameter (ID) of 3 inches.


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Provide a rain guard at the top terminus of the vent riser that does not restrict the upward flow of

air or methane from the pipe.

Install a bug screen near the base or top of the riser so the pipes cannot be used as a corridor for

insects to the below‐slab area after expected ground settlement.

Terminate vent riser as follows:

5 feet above grade;

5 feet away from any window, door, roof hatch, opening, or air intake into the building; and

5 feet away from electrical devices.

RECOMMENDATIONS FOR CONTINUING GEOTECHNICAL SERVICES

Design and Consulting Services Throughout this report, we recommend that we provide additional geotechnical input during the

design and construction process. These recommendations are generally summarized in this section.

We recommend that, before construction begins, we:

Continue to meet with the design team periodically as design concepts and design documents

progress,

Provide an update to this report as part of final design process, if necessary, and

Review the final design plans to verify that the geotechnical engineering recommendations have

been properly interpreted and implemented into the design.

Construction Services During the construction phase of the project, we recommend retaining us to observe the following

activities:

Augercast pile installation;

Installation and testing of shoring system elements;

Placement and density testing of structural fill at the site (if any);

Installation of sub‐slab, foundation, and wall drainage;

Backfilling of utility trenches or around subgrade walls; and

Other observations as required by DPD.

We recommend we review the following contractor submittals:

Pile installation logs,

Shoring system displacement and monitoring results, and

Construction dewatering systems and quantities of water produced.


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We should also:

Attend meetings as needed and

Assist with other geotechnical engineering considerations that may arise during construction.

The purpose of our observations will be to verify compliance with design concepts and

recommendations, and to allow design changes or evaluation of appropriate construction methods in

case subsurface conditions differ from those anticipated before construction begins.

REFERENCES AASHTO 2014. AASHTO LRFD Bridge Design Specifications. American Association of State Highway and

Transportation Officials. Washington, D.C.

ASCE 2010. Minimum Design Loads for Buildings and Other Structures, ASCE Standard ASCE/SEI 7‐10.

Idriss, I.M. and R.W. Boulanger 2008. Soil Liquefaction During Earthquakes. EERI Publication, MNO‐12.

International Code Council 2012. 2012 International Building Code.

Landau Associates 2015. Geotechnical Pre‐Design Report, 4603 and 4609 Union Bay Place NE Property.

Seattle, Washington. February 10, 2015.

U.S. Navy 1982. Soil Mechanics, Design Manual 7.1, NAVFAC DM‐7.1/7.2.

WSDOT 2014. Geotechnical Design Manual M 46‐03.10. Washington State Department of

Transportation. August 2014.

L:\Notebooks\1917400_Union Bay Place Development Design\Deliverables\Reports\Draft Geotechnical Report\Union Bay Place Geotech

Report DRAFT.docx

N

Union Bay Place Development

Seattle, Washington

Vicinity Map19174-00 11/15

Figure

1

Sources: Esri, HERE, DeLorme, USGS, Intermap, increment P Corp., NRCAN,Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom,MapmyIndia, © OpenStreetMap contributors, and the GIS User Community

2,000 0 2,0001,000

Scale in Feet

Project Site

Doc

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TB-1-77

TB-3-77

TB-2-77

HC-101

B-1

B-2

B-3

HC-MW-101

HC-MW-102

N

0 40 80

Scale in Feet

Figure

19

17

40

0-0

01

(S

Pla

n).d

wg

11

/1

8/1

5E

AL

19174-00 11/15

Seattle, Washington


2

Site and Exploration Plan

HC-101

B-1

TB-1-77

Legend

Boring (Hart Crowser 2015)

Monitoring well

(Hart Crowser 2015)

Boring (by others 2015)

Boring (by others 1976)

Cross section

Bearing layer

HC-MW-101

A A'

A

A

'

B

B

'

1

2

1

4

1

6

1

8

2

0

2

2

2

4

2

6

2

8

3

0

3

2

20

Elevation

Elevation

Distance

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

70

0 100 200 300 361

A

Southwest

A'

Northeast

6

B-1

(9')

5

17

14

11

5

8

5

14

17

39

50/4"

10

B-2

(10')

4

5

13

2

3

2

11

27

31

50/4"

50/4"

2

HC-101

(8')

3

3

4

9

27

72

50/6"

65

50/5"

65/4"

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

? ??

?

?

?

HC-MW-102

(4')

HC-MW-101

(16')

B-B'

Figure

19

17

40

0-0

02

(X

Se

c).d

wg

11

/1

8/1

5E

AL

19174-00 11/15

Seattle, Washington


3

Generalized Subsurface Cross Section A-A'

Vertical Scale in Feet

Horizontal Scale in Feet

60300

0 15 30

Vertical Exaggeration x 2

Exploration number

(Offset distance)

Exploration location

Water level

Standard penetration resistance in

blows per foot

Screened interval

HC-101

(8')

9

Legend

Fill (ESU 1)

Peat (ESU 2)

Medium dense sand (ESU 3)

Very dense sand (ESU 4)

Bearing layer

Approximate bottom of excavation

?

Elevation

Elevation

Distance

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

70

0 100 200 219

TP-3-77

(15')

7

11

10

24

54/6"

90

50/5"

B

Northwest

B'

Southeast

HC-MW-101

(47')

2

HC-101

(49')

3

3

4

9

27

72

50/6"

65

50/5"

65/4"

18

8

4

4

2

4

34

87

50/6"

50/6"

50/4"

50/5"

B-3

(7')

A-A'

?

?

?

?

?

?

?

?

?

?

??

?

?

? ?

Figure

19

17

40

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02

(X

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19174-00 11/15

Seattle, Washington


4

Generalized Subsurface Cross Section B-B'

Vertical Scale in Feet

Horizontal Scale in Feet

60300

0 15 30

Vertical Exaggeration x 2

Exploration number

(Offset distance)

Exploration location

Water level

Standard penetration resistance in

blows per foot

Screened interval

HC-101

(49')

9

Legend

Fill (ESU 1)

Peat (ESU 2)

Medium dense sand (ESU 3)

Very dense sand (ESU 4)

Bearing layer

Approximate bottom of excavation

?

Figure

5

19174-00 11/15


Seattle, Washington

Cascadia Subduction Zone Earthquake Sources

1917400-A

D (

EQ

Souce

).cd

rE

AL

11/1

8/1

5

Not to Scale

Source

Cascadia Subduction Zone - Interface 9.0

Cascadia Subduction Zone - Intraslab 7.5

Crustal Faults 7.5

Note: Base map prepared from drawingprovided by USGS and the University ofWashington, 2001.

Maximum

Magnitude

2001

N

0 10 20

Scale in Miles

Figure

19

17

40

0-0

03

(F

au

ltZ

on

es).d

wg

11

/1

8/1

5E

AL

19174-00 11/15

Seattle, Washington


6

Regional Fault Zones

Seattle

Project Site

Figure

7

19174-00 11/15


Seattle, Washington

Design of Temporary Cantilevered or Single Support Soldier Pile Shoring

Dra

win

g3

.cdr

CA

D02/0

7/0

7

Active Earth Pressure Submerged Allowable Passive Earth Pressure

Y(D+2)(PSF)

2'

Base of ExcavationA (Cantilever Walls)

Base of Excavation

Tieback Anchors

Zone of Deformation

Ground Surface(Elevation Varies)

2S(qa)

(fs)

2'Not to Scale

C. Allowable Tieback Anchor Pullout Resistance

A. Lateral Soil Pressure B. Vertical Capacity ofSoldier Pile

Allowable values include FS = 2.

Verify with Load Test to 200% of Design Stress Level.See Text and Attachment 1.

D

Determine depth of embedment (D) bymoment equilibrium of lateral soil pressuresaround point A. Neglect moment resistance ofsoldier pile member at point A. D must also besufficient to provide necessary vertical capacity.

Active pressure is assumed to act over pile spacing.

Passive pressure is assumed to act over twice thegrouted soldier pile diameter or the pile spacing,whichever is smaller. Passive pressure includesfactor of safety of about 1.5.

It is assumed that the site is drained duringconstruction so that hydrostatic pressure does notact on the walls.

All dimensions in feet.

Do not use these design criteria for design of anyother type of shoring wall.

See Figure 9 to evaluate additional surcharge.

Refer to Figure 2 for elevation of the bearing layer (ESU 3) for tieback bond zone. Tieback no load zone above this line and zone of deformation, whichever is longer.

Use a design groundwater elevation of 32 feet.

Notes: 1.

2.

3.

4.

5.

6.

7.

8.

9.

A (Single Tieback Walls)

Neglect Shaft Resistance in Upper 2 Feet

Neglect Passive Resistance in Upper 2 Feet

D(FT)

B

(qa)(fs)

AllowableFriction

Allowable End Bearing

1.5 KSF4D < 40KSFB

Native Sand(ESU 3)

Recommended Minimum Embedment Depth10 Feet into Native Dense Sands

Allowable Friction(Adhesion)

2.0 KSFNative Sand(ESU 3)

1.

2.

qs

S

H(FT)

NOT TO SCALE

Location

40

Fill (submerged)

16Native (submerged)

19

q *0.5 (PSF)s

q = 250 psf (Traffic and Temporary Loads) + Additional Surcharge Loadss

Fill (dry)

Active Conditions(X)

60

26

29

At Rest Conditions(X)

–

320

240

Passive(Y)

Bearing Layer.Locate All Anchors

Behind this Line(See Note 8)

X

1

O60

H/4

Fig

ure

8

19174-0

011

/15

Unio

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1917400-AB (EPD).cdrEAL 11/12/15

Active Earth Pressure

Not to Scale

Ground Surface (Elevation Varies)

H(FT)

A. Lateral Soil Pressures

Determine depth of embedment (D) bymoment equilibrium of lateral soil pressuresaround point A. Neglect moment resistance ofsoldier pile member at point A. D must also besufficient to provide necessary vertical capacity.

Active pressure is assumed to act over pile spacing.

Passive pressure is assumed to act over twice thegrouted soldier pile diameter or the pile spacing,whichever is smaller. Passive pressure includesfactor of safety of about 1.5.

It is assumed that the site is drained so that hydrostatic pressure does not act on the walls. If wall is not drained, use the hydrostatic pressure shown in this figure

All dimensions in feet.

Do not use these design criteria for design ofany other type of shoring wall.

See Figure 9 to evaluate additional surcharge pressures.

Use a design groundwater elevation of 32 feet.

Notes: 1.

2.

3.

4.

5.

6.

7.

8.

Base of Excavation

(qa) (qa)

(fs)

(fs)

2'Not to Scale

AllowableFriction

Allowable End Bearing

Recommended Minimum Embedment Depth10 Feet into Native Dense Sands

1.5 KSF

D(FT)

4D < 40KSFB

Native Sand

B (FT)

Location Active Conditions

Native Sand (Dry) X = 40

Native Sand (Submerged) Y = 19

q *0.5 (PSF) s

S

qs

2S

q = 250 psf (Traffic and Temporary Loads) + Additional Surcharge Loadss

B. Vertical Capacity ofSoldier Pile

Neglect ShaftResistance inUpper 2 Feet

DGW

+

62.4*(H ) (PSF) GW7H

Seismic Lateral Surcharge

+

X(D )+Y(H )(PSF)GW GW

Net HydrostaticPressure

At Rest Conditions

X = 60

Y = 29

HGW

Fig

ure

9

17194-0

011

/15

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Su

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e P

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Pre

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1917400-AC (EPD).cdrEAL 11/18/15

B(1). Small Isolated Footing

Cross Section ViewA. Strip Footing Cross Section View

C. Continuous Wall Footing Parallel to Excavation Cross Section View

1. Lateral pressures from adjacent structures should be added to lateral pressures on Figures 7 and 8.2. Wall footings acting other than parallel to the excavation can be treated as series of discrete point loads, using Approach B.3. Contact Hart Crowser for surcharge recommendations, if necessary.

Notes:

1

19174‐00 November 18, 2015

DRAFT

ATTACHMENT 1 Tieback Anchor Testing Program

19174‐00 November 18, 2015

DRAFT

ATTACHMENT 1

Tieback Anchor Testing Program Conduct the performance and proof tests as follows:

Performance Test

At least two performance tests should be completed before installation of production anchors. Each

performance test should be conducted according to the following procedure:

1. The geotechnical engineer will select the testing locations with input from the shoring

subcontractor.

2. The maximum stress in the prestressing steel should not exceed 80 percent of the ultimate

tensile strength during performance testing [based on the Post Tensioning Institute manual].

The soldier pile and tieback may require extra reinforcement to permit stressing to 200

percent of design load as required for the performance test.

3. The performance test will measure anchor stress and displacement incrementally to values of

unit skin friction equal to 200 percent of the design load. Load the anchor and measure

deflections following the load sequence in Table 1‐1.

Table 1-1 – Performance Test for Temporary Shoring

Load Level Hold Time Load Level Hold Time

AL Until Stable 1.75DL Until Stable

0.25DL 10 min 1.50DL Until Stable





1.50DL 60 min (Creep) 0.25DL Until Stable

1.75DL 10 min AL Until Stable

2.00DL 10 min

4. For 10‐minute hold times, obtain and record deflection measurements during loading at

intervals of 30 seconds, 1 minute, 2 minutes, 3 minutes, 5 minutes, 6 minutes, and 10 minutes.

Measurements shall be made to an accuracy of 0.01 inch.

5. Perform a creep test at the 150 percent of design stress reading by holding the load constant

to within 50 psi and recording readings at 30 seconds, 1 minute, 2 minutes, 3 minutes, 5

minutes, 6 minutes, and 10 minutes, 20 minutes, 30 minutes, 50 minutes, and 60 minutes.

6. A successful test does not experience pullout failure, holds the maximum test unit stress

without considerable creep, and satisfies the apparent free length criteria.

Pullout failure occurs when test measurements no longer exhibit a linear or near‐linear

relationship between unit stress and movement over the entire 200 percent stress range.

A-2 | Union Bay Place Development

19174‐00 November 18, 2015

DRAFT

Noticeable creep is defined as a rate of movement of not more than 0.04 inch between

the 1‐ and 10‐minute readings, or not more than 0.08 inch between the 6‐ and 60‐minute

readings. If the reading does not stabilize to 0.08 inch or less per log cycle of time, the test

shall be considered to fail the creep criteria.

Minimum apparent free length, based on the measured elastic and residual movement,

should be greater than 80 percent of the designed free length plus the jack length.

7. Perform tests without backfill ahead of the anchor, if the hole will remain open, to avoid any

contributory resistance by the backfill. If the hole will not remain open during testing, provide

a bond breaker on the tie rods and backfill the no load zone with a non‐cohesive non‐

structural mixture.

Proof Test

For each production tieback anchor, follow the proof testing procedures outlined below:

1. Load each anchor to 133 percent of the design load in increments of approximately 25 percent

of the design load (i.e., 0.25 DL, 0.50 DL, 0.75 DL, 1.00 DL, 1.25 DL, and 1.33 DL). The maximum

stress in the prestressing steel should not exceed 80 percent of the ultimate tensile strength

during proof testing.

2. Hold each incremental load for a period long enough to obtain a stable deflection

measurement while recording deflections at each load increment. Hold the 133 percent load

for a minimum of 10 minutes, recording the movement at times of 30 seconds, 1 minute, 2

minutes, and 5 minutes, 6 minutes, and 10 minutes.

3. A successful test is one that meets the same acceptance criteria as performance anchors,

except that the creep portion of the test need not exceed 10 minutes if the 10‐minute creep

criteria is meet.

4. Following proof loading, lock off each tieback anchor to 80 to 100 percent of the design load,

except as specified.

19174‐00 November 18, 2015

DRAFT

ATTACHMENT 2 Shoring Monitoring Program

19174‐00 November 18, 2015

DRAFT

ATTACHMENT 2

Shoring Monitoring Program A shoring monitoring program provides early warning if the shoring does not perform as anticipated.

We recommend that the following components be included in the shoring monitoring program during

construction:

Adjacent building surveys;

Optical surveying; and

Geotechnical instrumentation (Inclinometer).

All monitoring data should be submitted to Hart Crowser for weekly review. The data will be included

in our field transmittals to the project team and DPD during construction. Details of our expectations

for shoring monitoring are included below.

Adjacent Building Surveys

We recommend that adjacent buildings be surveyed before, during, and after construction. The pre‐

construction survey will establish the baseline of existing conditions (e.g., identifying the size and

locations of any cracks). The surveys should consist of a videotape and/or photographs of the interior

and exterior of adjacent buildings and detailed mapping of all cracks. Any existing cracks could be

monitored with a crack gauge.

Optical Surveying

We recommend optical surveys of horizontal and vertical movements of: (1) the surface of the

adjacent streets, (2) buildings on and adjacent to the site, and (3) the shoring system itself. The

contractor, in coordination with the geotechnical engineer, should establish two reference lines

adjacent to the excavation at horizontal distances back from the excavation face of about 1/3 H and H,

where H is the final excavation height. Typically, these lines will be established near the curb line and

across the street from the excavation face. The points on the adjacent buildings can be set either at

the base or on the roof of the buildings.

Shoring system monitoring should include measuring vertical and horizontal movement at the top of

every other soldier pile, and any geotechnical instrumentation (e.g., inclinometers) used for the

project.

The measuring system for the shoring monitoring should have an accuracy of at least 0.005 foot. All

reference points on the ground surface should be installed and read before excavation begins. The

frequency of readings will depend on the results of previous readings and the rate of construction. At

a minimum, readings on the external points should be taken once a week through construction until

below‐grade structural elements (floors, decks, columns, etc.) are completed, or as specified by the

structural and geotechnical engineers. Readings on the top of soldier piles and the face of existing

buildings on or adjacent to the property should be taken at least twice a week during this time. We


19174‐00 November 18, 2015

DRAFT

recommend that an independent surveyor hired by the owner to record the data at least once per

week with the other reading taken by the surveyor or contractor.

Geotechnical Instrumentation (Inclinometer)

We recommend installing inclinometer casings behind the shoring along the building to the north. The

casings should extend at least 10 feet below the bottom of the soldier piles. The number and location

of the casings should be coordinated with Hart Crowser and the contractor. Hart Crowser can be hired

to install the casings behind the shoring using a subcontracted driller; or, the shoring contractor may

install the inclinometer casings. We recommend inclinometer surveys at least once per week during

shoring construction. After the perimeter footing has been placed and cured, Hart Crowser may elect

to reduce the inclinometer survey frequency.

19174‐00 November 18, 2015

DRAFT

APPENDIX A Field Exploration Methods and Analysis

19174‐00 November 18, 2015

DRAFT

APPENDIX A

Field Exploration Methods and Analysis This appendix documents the processes Hart Crowser used to determine the nature of the site soil and

groundwater. This appendix includes information on the following subjects:

Explorations and Their Location;

Hollow‐Stem Auger Borings;

Standard Penetration Test Procedures;

Monitoring Well Installation; and

Water Level Measurement.

Explorations and Their Location Subsurface explorations for this project included one hollow‐stem auger (HSA) boring. The exploration

log in this appendix shows our interpretation of the drilling, excavation, sampling, and testing data.

The log indicates the depth where soils change. Note that the actual change may be gradual. In the

field, we classified the samples taken from the exploration according to the methods presented on

Figure A‐1 ‐ Key to Exploration Logs. This figure also provides a legend explaining the symbols and

abbreviations used in the logs.

Figure 2 illustrates the horizontal locations of explorations, which are based on field measurements

from existing physical features. The elevations on the logs are taken from the elevation contours

shown on Figure 2 that were provided to us. The vertical datum is NAVD88.

Hollow-Stem Auger Borings One HSA boring, designated HC‐101, was drilled on September 28, 2015 to a final depth of 36.3 feet

below the ground surface. The boring was completed using a Mobile B‐60 track‐mounted drill rig with

a 4.25‐inch inside diameter HSA. The boring was advanced by Holt Services, Inc., and continuously

observed by a geologist from Hart Crowser. A detailed field log was prepared. Samples were obtained

at 2.5‐ to 5‐foot‐depth intervals using standard penetration test procedures. Drilling fluid was

continually added to the augers and maintained at a level to control heaving conditions at the bottom

of the auger.

The boring logs is presented on Figure A‐2.

Standard Penetration Test Procedures The standard penetration test (SPT) method (as described in ASTM D 1586) was used to obtain

disturbed samples. This test is an approximate measure of soil density and consistency. To be useful,

the results must be used with engineering judgment in conjunction with other tests. The SPT test

employs a standard 2‐inch‐outside‐diameter split‐spoon sampler. Using a 140‐pound hammer, free‐

falling 30 inches, the sampler is driven into the soil for 18 inches. The number of blows required to


19174‐00 November 18, 2015

DRAFT

drive the sampler the last 12 inches only is the Standard Penetration Resistance. This resistance, or

blow count, measures the relative density of granular soils and the consistency of cohesive soils. If a

total of 50 blows are struck within any 6‐inch interval, the driving is stopped and the blow count is

recorded as 50 blows for the actual penetration distance. The blow counts are plotted on the boring

logs at their respective sample depths.

Monitoring Well Installation Monitoring wells were installed in borings HC‐MW‐101 and HC‐MW‐102 to allow for long‐term

groundwater level monitoring at the site. The monitoring wells were installed on September 28, 2015.

We used 2‐inch‐diameter Schedule 40 PVC riser pipe and 2‐inch‐diameter 0.020‐inch machine‐slotted

screen for the well casings and screens. The well screen and casing riser were lowered down through

the hollow‐stem auger. As the auger was withdrawn, No. 10/20 silica sand was placed in the annular

(ring‐shaped) space from the base of the boring to approximately 2 to 3 feet above the top of the well

screen. Well seals were constructed by placing bentonite chips in the annular space on top of the filter

sand to within 3 feet of the ground surface. The remaining annular space was backfilled with concrete

to complete the surface seal. For security, the monitoring wells were completed with a flush‐mounted

steel monument set in concrete. The monitoring wells were installed in accordance with Washington

State Department of Ecology regulations.

The monitoring well construction details are illustrated on the boring logs on Figures A‐3 and A‐4.

Water Level Measurement Water levels in the monitoring wells were measured using a water level probe, graduated in 0.01‐foot

increments.

9/15

Figure A-1

19174-00

Key to Exploration LogsSample Description

Very soft

Soft

Medium stiff

Stiff

Very stiff

Hard

ApproximateShear Strengthin TSF

0.125

0.25

0.5

1.0

0.25

0.5

1.0

2.0

Laboratory Test Symbols

Density/Consistency

SAND or GRAVELDensity

Very loose

Loose

Medium dense

Dense

Very dense

Soil descriptions consist of the following:Density/consistency, moisture, color, minor constituents, MAJOR CONSTITUENT,additional remarks.

StandardPenetrationResistance (N)in Blows/Foot

0

4

10

30

SILT or CLAYConsistency

to

to

to

to

>50

Liquid LimitNaturalPlastic Limit

Classification of soils in this report is based on visual field and laboratoryobservations which include density/consistency, moisture condition, grain size, andplasticity estimates and should not be construed to imply field nor laboratory testingunless presented herein. Visual-manual classification methods of ASTM D 2488were used as an identification guide.

GS

CN

UU

CU

CD

QU

DS

K

PP

TV

CBR

MD

AL

PID

CA

DT

OT

Groundwater Seepage(Test Pits)

Sampling Test Symbols

to

to

to

to

to

>30

<0.125

to

to

to

to

>2.0

Trace

Slightly (clayey, silty, etc.)

Clayey, silty, sandy, gravelly

Very (clayey, silty, etc.)

5

12

30

12

30

50

<5

-

-

-

Water Content in Percent

Little perceptible moisture

Some perceptible moisture, likely below optimum

Likely near optimum moisture content

Much perceptible moisture, likely above optimum

Soil density/consistency in borings is related primarily to the StandardPenetration Resistance. Soil density/consistency in test pits and probes isestimated based on visual observation and is presented parenthetically on thelogs.

4

10

30

50

StandardPenetrationResistance (N)in Blows/Foot

2

4

8

15

30

0

2

4

8

15

MoistureDry

Damp

Moist

Wet

Estimated PercentageMinor Constituents

1.5" I.D. Split Spoon

Shelby Tube (Pushed)

Cuttings

Grab (Jar)

Bag

Core Run

3.0" I.D. Split Spoon

Grain Size Classification

Consolidation

Unconsolidated Undrained Triaxial

Consolidated Undrained Triaxial

Consolidated Drained Triaxial

Unconfined Compression

Direct Shear

Permeability

Pocket Penetrometer

Approximate Compressive Strength in TSF

Torvane

Approximate Shear Strength in TSF

California Bearing Ratio

Moisture Density Relationship

Atterberg Limits

Photoionization Detector Reading

Chemical Analysis

In Situ Density in PCF

Tests by Others

Groundwater Level on Dateor (ATD) At Time of Drilling

Groundwater Indicators

Sample Key

2350/3"

S-1

SampleNumber

Blows per6 inches

12

Sample RecoverySample Type

KE

Y S

HE

ET

1

91

74

00

-BL

.GP

J

HC

_C

OR

P.G

DT

1

1/3

/15

LETTERGRAPH

SYMBOLSMAJOR DIVISIONS

SOIL CLASSIFICATION CHART

PT

OH

CH

MH

OL

CL

ML

SC

SM

SP

COARSEGRAINED

SOILS

SW

TYPICALDESCRIPTIONS

WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES, LITTLE OR NOFINES

POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES, LITTLEOR NO FINES

SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES

GC

GM

GP

GW

CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES

WELL-GRADED SANDS, GRAVELLYSANDS, LITTLE OR NO FINES

POORLY-GRADED SANDS,GRAVELLY SAND, LITTLE OR NOFINES

SILTY SANDS, SAND - SILTMIXTURES

CLAYEY SANDS, SAND - CLAYMIXTURES

INORGANIC SILTS AND VERY FINESANDS, ROCK FLOUR, SILTY ORCLAYEY FINE SANDS OR CLAYEYSILTS WITH SLIGHT PLASTICITY

INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS

ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY

INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS FINE SAND ORSILTY SOILS

INORGANIC CLAYS OF HIGHPLASTICITY

ORGANIC CLAYS OF MEDIUM TOHIGH PLASTICITY, ORGANIC SILTS

PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTS

CLEANGRAVELS

GRAVELS WITHFINES

CLEAN SANDS

(LITTLE OR NO FINES)

SANDS WITHFINES

LIQUID LIMITLESS THAN 50

LIQUID LIMITGREATER THAN 50

HIGHLY ORGANIC SOILS

NOTE: DUAL SYMBOLS ARE USED TO INDICATE BORDERLINE SOIL CLASSIFICATIONS

GRAVELAND

GRAVELLYSOILS

(APPRECIABLEAMOUNT OF FINES)

(APPRECIABLEAMOUNT OF FINES)

(LITTLE OR NO FINES)

FINEGRAINED

SOILS

SANDAND

SANDYSOILS

SILTSAND

CLAYS

SILTSAND

CLAYS

MORE THAN 50%OF MATERIAL ISLARGER THANNO. 200 SIEVE

SIZE

MORE THAN 50%OF MATERIAL ISSMALLER THANNO. 200 SIEVE

SIZE

MORE THAN 50%OF COARSEFRACTION

PASSING ON NO.4 SIEVE

MORE THAN 50%OF COARSEFRACTION

RETAINED ON NO.4 SIEVE

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

S-10

S-11

S-12

2

1

1

4

4

3

15

13

5

37

36

1

1

1

1

4

11

33

50/6''

23

40

65/4''

1

2

2

3

5

16

39

42

50/5''

ATD

GS

GS

GS

GS

SM

SP-SM

SP-SM

SM

8 inches of Asphalt over loose, moist, brownto dark brown, silty SAND with scattered darkbrown organics. (FILL)

Gravelly.

Occasional wood fragments.

Loose to medium dense, grayish brown,slightly silty, fine to medium SAND.

Very dense, wet, gray, slightly silty to silty,fine to medium SAND with occasional gravel.

Slightly sandy SILT layers.

Very dense, wet, gray, silty, fine SAND withoccasional gravel.

Moist.

Bottom of Boring at 36.3 Feet.

Started 09/28/15.

Completed 09/28/15.

0

5

10

15

20

25

30

35

40

45

50+

100+

Depthin Feet

20 60

0 10 20 40

80


30

Boring Log HC-101

LABTESTS

STANDARDPENETRATION RESISTANCE

Sample Blows per Foot

Drill Equipment: Mobile B-60 w/HSAHammer Type: SPT w/ 140 lb. Automatic hammerHole Diameter: 8 inchesLogged By: B. McDonald Reviewed By: J. Bruce

0 40

GraphicLog Soil Descriptions

USCSClass

Location: Lat: 47.662840 Long: -122.294780Approximate Ground Surface Elevation: 45 FeetHorizontal Datum: WGS84Vertical Datum: NAVD88

19174-00

Figure A-2

9/15

1. Refer to Figure A-1 for explanation of descriptions and symbols.2. Soil descriptions and stratum lines are interpretive and actual changes may be gradual.3. USCS designations are based on visual manual classification (ASTM D 2488) unless otherwise

supported by laboratory testing (ASTM D 2487).4. Groundwater level, if indicated, is at time of drilling (ATD) or for date specified. Level may vary

with time.

NE

W B

OR

ING

LO

G

19

17

40

0-B

L.G

PJ

HC

_C

OR

P.G

DT

1

1/6

/15

Flush mountmonument

Concrete

Bentonitechips

10-20 Silicasand

Screened 2"PVC

ATD

-


Started 09/28/15.

Completed 09/28/15.

Ecology Well Tag #BJE-898

0

5

10

15

20

25

30

35

40

45

50+

100+

Depthin Feet

20 60

0 10 20 40

80


30

Monitoring Well Log HC-MW-101

LABTESTS



Drill Equipment:Hammer Type:Hole Diameter: inchesLogged By: B. McDonald Reviewed By: J. Bruce

0 40

GraphicLog

WellConstructionSoil Descriptions

USCSClass

Location:Approximate Ground Surface Elevation: 45 FeetHorizontal Datum: WGS84Vertical Datum: NAVD88

19174-00

Figure A-3

9/15



with time.

NE

W B

OR

ING

LO

G

19

17

40

0-B

L.G

PJ

HC

_C

OR

P.G

DT

1

1/6

/15

Flush mountmonument

Concrete

Bentonitechips

10-20 Silicasand

Screened 2"PVC

-


Started 09/28/15.

Completed 09/28/15.

Ecology Well Tag #BJE-899

0

5

10

15

20

25

30

35

40

45

50+

100+

Depthin Feet

20 60

0 10 20 40

80


30

Monitoring Well Log HC-MW-102

LABTESTS



Drill Equipment:Hammer Type:Hole Diameter: inchesLogged By: B. McDonald Reviewed By: J. Bruce

0 40

GraphicLog

WellConstructionSoil Descriptions

USCSClass

Location: Lat: 47.662400 Long: -122.295470Approximate Ground Surface Elevation: 42 FeetHorizontal Datum: WGS84Vertical Datum: NAVD88

19174-00

Figure A-4

9/15



with time.

NE

W B

OR

ING

LO

G

19

17

40

0-B

L.G

PJ

HC

_C

OR

P.G

DT

1

1/6

/15

19174‐00 November 18, 2015

DRAFT

APPENDIX B Laboratory Testing Program

19174‐00 November 18, 2015

DRAFT

APPENDIX B

Laboratory Testing Program A laboratory testing program was performed for this study to evaluate the basic index and

geotechnical engineering properties of the site soils. The tests performed and the procedures followed

are outlined below.

Soil Classification Soil samples from the explorations were visually classified in the field and then taken to our laboratory

where the classifications were verified in a relatively controlled laboratory environment. Field and

laboratory observations include relative density/consistency, moisture condition, and grain size

estimates.

The classifications of selected samples were checked by laboratory tests such as grain size analyses.

Classifications were made in general accordance with the Unified Soil Classification (USC) System,

ASTM D 2487, as presented on Figure B‐1.

Water Content Determinations Water content was determined for most samples recovered in the explorations in general accordance

with ASTM D 2216, as soon as possible following their arrival in our laboratory. Water contents were

not determined for very small samples or samples where large gravel contents would result in

unrepresentative values. The results of these tests are plotted or presented at the respective sample

depth on the exploration logs. In addition, water contents are routinely determined for samples

subjected to other testing. These are also presented on the exploration logs.

Grain Size Analysis Grain size distribution was analyzed on representative samples in general accordance with ASTM D

422. Wet sieve analysis was used to determine the size distribution greater than the U.S. No. 200 mesh

sieve. The results of the tests are presented as curves on Figures B‐2 and B‐3 plotting percent finer by

weight versus grain size.

C H

C H

ALine

O H PtC L

C L

C L - M L

O L M H

M L

or O L

M H or O H

SRF Grain Size (B-1).cdr 3/06

Fine-Grained Soils

Coarse-Grained Soils

Size of Opening In Inches

12

30

0

6

20

0

41

00

42

80

11 /2

60

1

40

3/4

30

20

5/8

10

1/2

3/8

1/4

10

8

20

6

40

4

60

3 2 1 .8 .6 .4

10

0

.3

20

0

.2

.06

.06

.081

.04

.04

.03

.03

.02

.02

.01

.01

.00

8.0

08

.00

6.0

06

.00

4.0

04

.00

3.0

03

.00

2.0

02

.00

1.0

01

Number of Mesh per Inch(US Standard)

Grain Size in Millimetres

COBBLES GRAVEL SAND SILT and CLAY

Coarse-Grained Soils Fine-Grained Soils

Grain Size in Millimetres

G W

M L

G P G M G C S W S P S M S C

Clean GRAVEL <5% fines Clean SAND <5% finesGRAVEL with >12% fines SAND with >12% fines

GRAVEL >50% coarse fraction larger than No. 4

Soils with Liquid Limit <50%

SAND >50% coarse fraction smaller than No. 4

Coarse-Grained Soils >50% larger than No. 200 sieve

Fine-Grained Soils >50% smaller than No. 200 sieve

* *

G W and S W & 1<_ <_ 3D >4 for G W

D >6 for S W

60

10

(D )

D X D

30

10 60

2

G M and S M Atterberg limits below A line with PI <4

G P and S P Clean GRAVEL or SAND not meetingrequirements for G W and S W

G C and S C Atterberg limits above A Line with PI >7

* Coarse-grained soils with percentage of fines between 5 and 12 are considered borderline cases requiring use of dual symbols.

D , D , and D are the particles diameter of which 10, 30, and 60 percent, respectively, of the soil weight are finer.10 30 60

Soils with Liquid Limit >50%

SILT SILTCLAY CLAYOrganic Organic HighlyOrganicSoils

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90 100

Liquid Limit

Pla

sticity I

nd

ex

60

50

40

30

20

10

0

Unified Soil Classification (USC) SystemSoil Grain Size

3

19174-00Figure B-1

9/15

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.1110100

#30

#40

Client:

1-1

/2 in.

D15D30

12.8

6.5

30.1

Source: HC-101Source: HC-101Source: HC-101

Figure B-2

D60D85PI

silty gravelly SAND

slightly silty, gravelly SAND

very silty SAND, trace gravel

3/4

in.

1/2

in.

3/8

in.

#100

D50

#4

#10

Depth: 7.5 to 9.0Depth: 12.5 to 14.0Depth: 17.5 to 19.0

Project: Union Bay Place

17.7

13.7

4.7

69.5

79.8

65.2

% COBBLES

6 in.

3 in.

2 in.

1 in.

MATERIAL DESCRIPTION USCS NAT. MOIST.

% CLAY

0.404

0.419

0.233

0.22

0.284

#200

LL Cu

19174-00

GRAIN SIZE - mm

0.591

0.574

0.322

% SILT

Remarks:

Particle Size Distribution Test Report

% GRAVEL % SAND

26.1%

16.9%

18.5%

PE

RC

EN

T F

INE

R

SM

SP-SM

SM

9/15

#20

#140

1.02

#60

0.0

0.0

0.0

0.139 4.14

5.636

3.983

0.982

0.091

0.18

CcD10

Sample No.: S-4Sample No.: S-6Sample No.: S-8

GR

AIN

SIZ

E

19

17

40

0-B

L.G

PJ

HC

_C

OR

P.G

DT

1

1/3

/15

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.1110100

#30

#40

Client:

1-1

/2 in.

D15D30

23.8

Source: HC-101

Figure B-3

D60D85PI

silty SAND, trace gravel

3/4

in.

1/2

in.

3/8

in.

#100

D50

#4

#10

Depth: 30.0 to 31.5

Project: Union Bay Place

2.2 74.0

% COBBLES

6 in.

3 in.

2 in.

1 in.

MATERIAL DESCRIPTION USCS NAT. MOIST.

% CLAY

0.177 0.099

#200

LL Cu

19174-00

GRAIN SIZE - mm

0.206

% SILT

Remarks:

Particle Size Distribution Test Report

% GRAVEL % SAND

15.2%

PE

RC

EN

T F

INE

R

SM

9/15

#20

#140

#60

0.0

0.37

CcD10

Sample No.: S-11

GR

AIN

SIZ

E

19

17

40

0-B

L.G

PJ

HC

_C

OR

P.G

DT

1

1/3

/15

19174‐00 November 18, 2015

DRAFT

APPENDIX C Historical Explorations

19174‐00 November 18, 2015

DRAFT

APPENDIX C

Historical Explorations In addition to the explorations and laboratory test results presented in Appendices A and B, we

reviewed previous explorations and lab test results by others to gain an understanding of the

subsurface conditions within unexplored portions of the site. Logs by others are included as they were

produced by others for reference only and Hart Crowser is not responsible for the accuracy or

completeness of the information presented in the logs. Approximate locations of the previous

explorations by others are shown on Figure 2; actual locations may differ from those shown.

6

5

17

14

11

5

8

5

14

17

PID=0W = 20

AL

PID=0W = 22

PID=0.3W = 12

PID=0.1

PID=0.4W = 12

PID=0

PID=0W = 22

PID=0

PID=0.2W = 278

PID=0.3

b2

b2

b2

b2

b2

b2

b2

b2

b2

b2b

ACGM

ML

ML

ACSM

SM

SM

PT

ML/CLSM

SM

Asphalt Pavement (~0.4 feet thickness)

Gray, sandy GRAVEL with silt (crushed, 11/4 inch minus); no odors, sheen, orstaining observed

(FILL)

Mottled gray and brown, very sandySILT/CLAY with gravel and organics; noodors, sheen, or staining observed(medium stiff, wet)

Mottled gray and brown, gravelly, sandySILT; no odors, sheen, or stainingobserved (medium stiff, wet)

Asphalt pavement or debris

Gray, very gravelly, fine to medium SANDwith silt and trace organics; no odors,sheen, or staining observed (mediumdense, moist)

Mottled gray and brown, gravelly, silty tovery silty, fine to medium SAND; no odors,sheen, or staining observed (loose tomedium dense, wet)

Brown, gravelly, silty, fine to mediumSAND to trace gravel and fine organics; noodors, sheen, or staining observed (loose,moist to wet)

- concrete debris

Brown, PEAT (massive with somefiberous); no odors, sheen, or stainingobserved (stiff, moist to wet)

(ALLUVIUM)

Gray brown, clayey SILT with sand; noodors, sheen, or staining observed (stiff,moist to wet)

Mottled light brown and reddish brown,very silty, fine to medium SAND with tracegravel; no odors, sheen, or stainingobserved (medium dense, wet)

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

S-10AS-10B

278

SPT N-Value

20 40 60 80

Moisture Content (%)

20 40 60 80

Fines Content (%)

20 40 60 800

5

10

15

20

25

30

35

Ele

vatio

n (f

t)

40

35

30

25

20

15

10

Notes:

Sam

pler

Typ

e

Blo

ws/

Foo

t

Tes

t Dat

a

LiquidLimit

Sam

ple

Num

ber

& In

terv

al

LAI Project No: 1379002.020.021

Non-Standard N-Value

Gra

phic

Sym

bol

Dep

th (

ft)

US

CS

Sym

bol

Logged By:

Drilled By:

SOIL PROFILE

Ground Elevation (ft):

Drilling Method:

Cascade Drilling Inc.

SAMPLE DATA

Date:

Hollow-Stem Auger

PlasticLimit

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H

B-1

43

1. Stratigraphic contacts are based on field interpretations and are approximate.2. Reference to the text of this report is necessary for a proper understanding of subsurface conditions.3. Refer to "Soil Classification System and Key" figure for explanation of graphics and symbols.

Gro

undw

ater

Log of Boring B-1 A-2(1 of 2)

Figure

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H

4603 and 4609 Union BayPlace NE

Seattle, Washington

16.5

ft A

TD

39

50/4"

PID=0.1W = 16

GS

PID=050/4"

b2

b2

SM

SP

(ADVANCE OUTWASH)Light brown, gravelly, fine to mediumSAND with silt to silty, fine to mediumSAND with gravel; no odors, sheen, orstaining observed (dense, wet)

Light brown, fine to medium SAND; noodors, sheen, or staining observed (verydense, wet)

S-11

S-12

Boring CompletedTotal Depth of Boring = 40.8 ft.

SPT N-Value

20 40 60 80


20 40 60 80

Fines Content (%)

20 40 60 8035

40

45

50

55

60

65

70

Ele

vatio

n (f

t)

5

Notes:

Sam

pler

Typ

e

Blo

ws/

Foo

t

Tes

t Dat

a

LiquidLimit

Sam

ple

Num

ber

& In

terv

al

LAI Project No: 1379002.020.021


Gra

phic

Sym

bol

Dep

th (

ft)

US

CS

Sym

bol

Logged By:

Drilled By:

SOIL PROFILE


Drilling Method:


SAMPLE DATA

Date:

Hollow-Stem Auger

PlasticLimit

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H

B-1

43


Gro

undw

ater


Figure

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H


Seattle, Washington

10

4

5

13

2

3

2

11

27

31

PID=0W = 19

PID=0.1

PID=0W = 23

PID=0.2

PID=0.2W = 17

PID=0.1W = 17

AL

PID=0

PID=0W = 27

PID=0

PID=0.1W = 22

50/

b2

b2

b2

b2

b2

b2

b2

b2

b2

b2

ACSM

SM

SM/ML

SM

ML/CLSM

SP

SP/SM

Asphalt Pavement (~0.4 feet thickness)

Mottled gray and brown, gravelly, silty, fineto medium SAND and silty, fine to mediumSAND with gravel; no odors, sheen, orstaining observed (loose to medium dense,moist to wet)

(FILL)

- burnt wood debris

- painted wood debris and fine organics

Brown, silty, gravelly, fine to mediumSAND with asphalt pavement/debris; noodors, sheen, or staining observed(medium dense, moist)

Mottled brown and gray, very sandy SILTwith gravel and fine organics andinterbedded silty, fine SAND; no odors,sheen, or staining observed (very loose toloose/soft, wet)

Brown, silty, very gravelly, fine to mediumSAND; no odors, sheen, or stainingobserved (very loose to loose, wet)

Light brown to yellow brown, fine sandy,clayey SILT with gravel; no odors, sheen,or staining observed (medium dense/verystiff, wet)

(ADVANCE OUTWASH)

Light brown, silty to very silty, fine tomedium SAND with fine gravel; no odors,sheen, or staining observed (mediumdense/very stiff, wet)

Light brown, fine SAND; no odors, sheen,or staining observed (dense, wet)

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

S-10

SPT N-Value

20 40 60 80


20 40 60 80

Fines Content (%)

20 40 60 800

5

10

15

20

25

30

35

Ele

vatio

n (f

t)

45

40

35

30

25

20

15

10Notes:

Sam

pler

Typ

e

Blo

ws/

Foo

t

Tes

t Dat

a

LiquidLimit

Sam

ple

Num

ber

& In

terv

al

LAI Project No: 1379002.020.021


Gra

phic

Sym

bol

Dep

th (

ft)

US

CS

Sym

bol

Logged By:

Drilled By:

SOIL PROFILE


Drilling Method:


SAMPLE DATA

Date:

Hollow-Stem Auger

PlasticLimit

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H

B-2

45


Gro

undw

ater


Figure

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H


Seattle, Washington

12.0

ft A

TD

50/4"

50/4"

PID=0.1W = 14

PID=0

4"

50/4"

b2

b2

SP/SM

SP

Light brown, gravelly, fine to mediumSAND and interbedded fine to mediumSAND with silt and trace gravel; no odors,sheen, or staining observed (very dense,wet)

Light brown, fine to medium SAND; noodors, sheen, or staining observed (verydense, wet)

S-11

S-12


SPT N-Value

20 40 60 80


20 40 60 80

Fines Content (%)

20 40 60 8035

40

45

50

55

60

65

70

Ele

vatio

n (f

t)

10

5

Notes:

Sam

pler

Typ

e

Blo

ws/

Foo

t

Tes

t Dat

a

LiquidLimit

Sam

ple

Num

ber

& In

terv

al

LAI Project No: 1379002.020.021


Gra

phic

Sym

bol

Dep

th (

ft)

US

CS

Sym

bol

Logged By:

Drilled By:

SOIL PROFILE


Drilling Method:


SAMPLE DATA

Date:

Hollow-Stem Auger

PlasticLimit

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H

B-2

45


Gro

undw

ater


Figure

1379

002.

020

.021

2/

10/1

5 N

:\PR

OJE

CT

S\1

379

002.

020

.02

1.G

PJ

SO

IL B

OR

ING

LO

G W

ITH

GR

AP

H


Seattle, Washington

18

8

4

4

2

4

34

87

50/6"

50/6"

PID=0W = 12

PID=0.1

PID=0W = 31

AL

PID=0W = 27

PID=0

PID=0W = 18

PID=0

PID=0W = 20PID=0

PID=0W = 21

PID=0

50/6"

50/6"

50/

b2

b2

b2

b2

b2

b2

b2

b2b2

b2

b2

SMSM

ML

SM

SP

SP

SM

SP

SP-SM

Crushed Rock(0.5 foot thickness)

Mottled gray and brown, silty, gravelly, fineto medium SAND; no odors, sheen, orstaining observed (medium dense, moist)

(FILL)

Gray Brown, CLAY with fine sand and thininterbedded silty, clayey, fine SAND; noodors, sheen, or staining observed(medium stiff to stiff, moist)

Brown, very silty, fine to medium SANDwith gravel; no odors, sheen, or stainingobserved (very loose, wet)

Light brown, gravelly, fine to mediumSAND; no odors, sheen, or stainingobserved (dense, wet)

(ADVANCE OUTWASH)

Reddish brown, fine to medium SAND withinterbedded gravelly, fine to mediumSAND; no odors, sheen, or stainingobserved (very dense, wet)

Light brown, very silty, fine to mediumSAND with gravel and interbedded finesandy SILT; no odors, sheen, or stainingobserved (very dense, wet)

Light brown, silty, fine SAND and fineSAND with silt; no odors, sheen, orstaining observed (very dense, wet)

Gray, gravel to very gravelly, fine tomedium SAND with silt; no odors, sheen,or staining observed (very dense, wet)

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8AS-8B

S-9

S-10

SPT N-Value

20 40 60 80


20 40 60 80

Fines Content (%)

20 40 60 80

(DO

E#:

BJA

-544

)W

EL

L D

ET

AIL

0

5

10

15

20

25

30

35

Ele

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t)

45

40

35

30

25

20

15

10Notes:

Sam

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Sam

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LAI Project No: 1379002.020.021


Gra

phic

Sym

bol

Dep

th (

ft)

US

CS

Sym

bol

Logged By:

Drilled By:

SOIL PROFILE


Drilling Method:


SAMPLE DATA

Date:

Hollow-Stem Auger

PlasticLimit

1379

002.

020

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Seattle, Washington

5.7

ft12

.5 ft

50/4"

50/5"

PID=0W = 14

PID=0

4"

50/5"

b2

b2

SP-SM

SP

Gray, gravel to very gravelly, fine tomedium SAND with silt; no odors, sheen,or staining observed (very dense, wet)

Gray, gravel to very gravelly, fine tomedium SAND with trace silt; no odors,sheen, or staining observed (very dense,wet)

S-11

S-12


SPT N-Value

20 40 60 80


20 40 60 80

Fines Content (%)

20 40 60 80

(DO

E#:

BJA

-544

)W

EL

L D

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35

40

45

50

55

60

65

70

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LAI Project No: 1379002.020.021


Gra

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Dep

th (

ft)

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Drilled By:

SOIL PROFILE


Drilling Method:


SAMPLE DATA

Date:

Hollow-Stem Auger

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Seattle, Washington

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.1110100

60126 1001.5 163

Fine

U.S. Sieve Numbers

3/8 140 200

Depth(ft)

NaturalMoisture (%)Symbol

U.S. Sieve Opening in Inches

14

Silt or ClayGravel

Unified SoilClassification

Grain Size in Millimeters

Per

cent

Fin

er b

y W

eigh

t4 10 303/4 3 20

Sand

Hydrometer

MediumCoarseCobbles

4

ExplorationNumber

408

SampleNumber

Coarse

1/2 50

Fine

6

Soil Description

SP-SM

SP

SM

S-11

S-10

S-9

Gravelly, fine to medium SAND with silt

Fine SAND with medium sand and trace silt

Silty, fine SAND

16

22

21

35.0

30.0

25.0

B-1

B-2

B-3

Grain Size Distribution A-5Figure

1379002.020.021 2/10/15 N:\PROJECTS\1379002.020.021.GPJ GRAIN SIZE FIGURE


Seattle, Washington

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100 110

CL

ExplorationNumber Depth

(ft)

PlasticityIndex(%)

CL-ML MH or OH

CH

ML or OL

ASTM D 4318 Test Method

NaturalMoisture

(%)

Unified SoilClassificationSymbol

ATTERBERG LIMIT TEST RESULTS

Soil Description

Liquid Limit (LL)

Pla

stic

ity In

dex

(PI)

SampleNumber

PlasticLimit(%)

LiquidLimit(%)

B-1

B-2

B-3

20

17

31

6

3

21

ML/CL

ML

CL

24

21

44

18

18

23

2.5

15.0

7.5

Very sandy, SILT/CLAY with gravel

Very sandy SILT with gravel

CLAY

S-1

S-6

S-3

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Seattle, WashingtonPlasticity Chart A-6

19174‐00 November 18, 2015

DRAFT

APPENDIX D Slug Testing

19174‐00 November 18, 2015

DRAFT

APPENDIX D

Slug Testing This appendix presents the results of slug testing that was conducted for the Union Bay Place

Development in Seattle, Washington. Slug tests were performed to determine hydraulic conductivity

of formation for use in estimating flow rates during dewatering.

Slug tests are performed by suddenly inserting or removing a solid PVC rod in a well and measuring the

recovery of the water levels during the test. A test conducted by the insertion of the PVC rod into the

well is referred to as a falling head test and the following removal of the rod is called a rising head test.

The water level data generated from the tests were analyzed using the commercial software

AquiferWin32 Version 3 (Environmental Simulations, Inc., 2003). The slug test analysis is based on the

Bouwer and Rice method (Bouwer and Rice 1976; Bouwer 1989) to obtain an estimated value of

hydraulic conductivity of the aquifer.

SLUG TESTING RESULTS Slug testing was conducted in wells HC‐MW‐101 and B‐3 on October 6, 2015. Slug tests were not

performed in well HC‐MW‐102 due to insufficient water within the well. A summary of monitoring

well construction details is provided in Table 1. Shallow soils at the project site consist of poorly

graded Sand, silty Sand, and poorly graded Sand with silt and gravel units. Stratigraphic units at HC‐

MW‐102 were inferred from log borings from Landau Associates boring B‐1 that was drilled in the

vicinity of HC‐MW‐102. The wells were screened in three stratigraphic units and are summarized

below:

HC‐MW‐101 was screened in the silty Sand and poorly graded Sand units;

HC‐MW‐102 was screened in the silty Sand unit; and

B‐3 was screened in poorly graded Sand with silt and gravel, and poorly graded Sand units.

A summary of slug testing results is provided in Table 2. Hydrographs of HC‐MW‐1‐1 and B‐3 are

provided as Figure 1. The slug test plots are provided as Figure 2 and Figure 3. Multiple sets of falling

and rising head tests were performed on each well. The results of the falling and rising head tests

compare favorably. Average hydraulic conductivities determined from slug tests range from 6.2 x 10‐4

to 1.9 x 10‐3 cm/sec (1.8 to 5.4 feet/day). This hydraulic conductivity range is typical for silt and silty

sand (Freeze and Cherry 1979).

REFERENCES Bouwer H. 1989. The Bouwer and Rice Slug Test – An Update. Ground Water 27(3): 304‐309.

Bouwer H. and R.C. Rice 1976. A Slug Test for Determining Hydraulic Conductivity of Unconfined

Aquifers with Completely or Partially Penetrating Wells. Water Resources Research 12(3): 423‐428.

Environmental Simulations, Inc. 2003. Guide to Using AquiferWin32 Version 3.


19174‐00 November 18, 2015

DRAFT

Freeze, R.A. and J.A. Cherry 1979. Groundwater. Prentice‐Hall, Englewood Cliffs, New Jersey.

Attachments: Table D‐1 – Monitoring Well Construction Summary Table D‐2 – Summary of Slug Test Results Figure D‐1 – HC‐MW‐101 and B‐3 Hydrographs Figure D‐2 – HC‐MW‐101 Representative Slug Tests Results Figure D‐3 – B‐3 Representative Slug Tests Results

Table D-1 - Monitoring Well Construction Summary

Well ID HC-MW-101 HC-MW-102 B-3Boring Depth in Feet 20.0 21.4 42.0Well Depth in Feet 20.0 21.4 40.0Screen Interval Depth in Feet 9.6 to 19.6 10.8 to 20.8 30.0 to 40.0Depth to Sediment in Feet (1) 19.7 20.2 39.8Depth to Water in Feet (1) 13.0 18.6 8.2Saturated Thickness in Feet 6.8 1.6 31.5Screened Interval Soil Description SM, SP SM* SP-SM**, SP**

Notes: (1) Depth to sediment and depth to water was measured on October 5, 2015. SM = Silty SAND. SP = Poorly graded SAND. NA = Data not available. * According to Landau Associates Log Boring of B-1. **According to Landau Associates Log Boring of B-3.

Hart Crowser 1798401\Slug Test Tables and Figures - Table 1

Table D-2 - Summary of Slug Test Results

K in ft/day K in cm/secFalling Head Test 1 5.4 1.9E-03Rising Head Test 2 6.0 2.1E-03Falling Head Test 3 4.5 1.6E-03Rising Head Test 4 6.0 2.1E-03Falling Head Test 5 4.3 1.5E-03Rising Head Test 6 6.0 2.1E-03

Average 5.3 1.9E-03NA NA NA NA

Average NA NAFalling Head Test 1 1.6 5.7E-04Rising Head Test 2 1.5 5.3E-04Falling Head Test 3 1.9 6.7E-04Rising Head Test 4 1.5 5.2E-04Falling Head Test 5 2.3 8.0E-04

Average 1.8 6.2E-04

Notes: NA = Data not available.

Bouwer and Rice

HC-MW-101

HC-MW-102

B-3

Well ID Test Type Test Number

Hart Crowser 1798401\Slug Test Tables and Figures - Table 2

19174-00 10/15

Figure

Union Bay PlaceSeattle, Washington

HC-MW-101 and B-3 Hydrographs

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HC-MW-101 Representative Slug Tests Results

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HC-MW-101 Test 3 - Falling Head

10-1

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Dis

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Time in Seconds Hydraulic Conductivity 1.6e-003 cm/sec

HC-MW-101 Test 2 - Rising Head

10-2

10-1

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0.0 8.0 16.0 24.0 32.0 40.0

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Figure


B-3 Representative Slug Tests Results

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B-3 Test 3 - Falling Head

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Dis

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union bay place geotech report draft

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