limited pavement/geotechnical investigation report

LIMITED PAVEMENT/GEOTECHNICAL INVESTIGATION REPORT

PROJECT:

PAVEMENT DISTRESS STUDY AT THE INTERSECTION OF WALNUT GROVE AVENUE AND VALLEY BOULEVARD

ROSEMEAD, CA 91770

FOR:

CITY OF ROSEMEAD

8838 EAST VALLEY BOULEVARD ROSEMEAD, CA 91770

PREPARED BY: GEO-ADVANTEC, INC.

457 W. ALLEN AVENUE, SUITE 113 SAN DIMAS, CALIFORNIA 91773

PROJECT NO. 17-1188 DECEMBER 13, 2017

Table of Contents

Subject Page

1. INTRODUCTION ......................................................................................................... 1

2. SITE CONDITIONS AND PAVEMENT DISTRESSES ............................................. 2

3. SCOPE OF SERVICES ................................................................................................. 2

4. FIELD EXPLORATORY WORKS .............................................................................. 3

5. SUBSURFACE CONDITIONS .................................................................................... 4

6. LABORATORY TESTING........................................................................................... 4

7. GROUNDWATER ........................................................................................................ 5

8. COLLAPSE POTENTIAL ............................................................................................ 5

9. CONCLUSIONS AND RECOMMENDATIONS ........................................................ 5

9.1. Discussion ............................................................................................................... 5

9.2. Recommended Rehabilitation ................................................................................. 6

9.2.1. Full Depth Removal and Reconstruction (FDRR) ........................................... 7

9.3. Utility Trench Backfilling ....................................................................................... 8

9.4. Temporary Excavations........................................................................................... 9

10. OBSERVATION AND TESTING ........................................................................... 10

11. CLOSURE ................................................................................................................ 10

457 West Allen Avenue, Suite 113. San Dimas, California 91773. Phone: (909) 305 – 0400. WWW.GeoAdvantec.com

Mr. Rafael Fajardo, P.E. December 13, 2017 Public Works Director Project No. 17-1188 City of Rosemead 8838 East Valley Boulevard Rosemead, CA 91770

Subject: Limited Pavement/Geotechnical Investigation Report Pavement Distress Study at the Intersection of Walnut Grove Avenue and Valley Boulevard Rosemead, CA 91770

1. INTRODUCTION

This report presents the results of a Limited Pavement/Geotechnical Investigation performed by

Geo-Advantec Inc. (GAI) for the Pavement Distress Study at the intersection of Walnut Grove

Avenue and Valley Boulevard, located within the City of Rosemead, California. This investigation

was performed to provide geotechnical and pavement information at the site, and to determine the

causes for distresses observed at the site, as described in the forthcoming sections of this report.

The report also includes our recommendations for the rehabilitation of the distresses from a

pavement/geotechnical standpoint.

The recommendations provided within this submittal are based on the results of our field

exploration, laboratory testing, engineering analyses and our experience from similar projects. Our

services were performed in general accordance with our Proposal No. 17-1188, dated August 30,

2017.

A vicinity map is presented as Figure A-1 within Appendix A. An aerial photo of the site has been

used as the base map to depict the approximate locations of the pavement distresses and the borings

performed, and is presented as Figure A-2 within Appendix A.

Our professional services have been performed using the degree of care and skill ordinarily

exercised, under similar circumstances, by reputable geotechnical consultants practicing in this or

similar localities. No other warranty, expressed or implied, is made as to the professional advice

included in this report. This report has been prepared for City of Rosemead (“the City”) and their

design consultant for the subject project. The report has not been prepared for use by other parties,

and may not contain sufficient information for the purposes of other parties or other uses. The

Geotechnical Engineer of Record should be allowed to review the plans for the proposed

Project No. 17-1188 Geo-Advantec, Inc. Page 2 of 11 December 13, 2017

development and perform such additional geotechnical analyses as may be required to confirm the

applicability of the recommendations contained in this report to the final design.

2. SITE CONDITIONS AND PAVEMENT DISTRESSES

The pavement distresses are located at the intersection of Walnut Grove Avenue and Valley

Boulevard, located in the City of Rosemead, California. The streets are in a medium traffic volume

area surrounded by commercial businesses on all side and is along a bus route in the west-east

direction. The main pavement distresses observed are as follows:

1. Depression – a localized low spot on the pavement surface. These spots are most

noticeable after a rain, when the depression is filled with water.

2. Shoving – plastic movement in the asphalt concrete that creates a localized bulging on

the surface

3. Rutting – the displacement of asphalt concrete that creates channels in the wheel path

on the surface.

Approximate locations of the observed depression and shoving distresses described are depicted

on Figure A-2 within Appendix A, and the photographs are shown in Appendix P. There are two

depressions observed at the intersection. The first one is a moderate sized depression located on

the southeast corner of the intersection (“corner depression”) as seen in Photo 1 within Appendix

P, and the second one is a large sized depression located in the center of the intersection on the

slow eastbound lane (“center depression”) as seen in Photos 3 and 4. Shoving was observed just

past the concrete bus pad on the eastbound lane as seen in Photo 5. There were also excess asphalt

spilling over into the concrete gutter at the same location. Moderate to high intensity rutting were

observed on all lanes on the eastbound and westbound directions.

The site is relatively flat with an approximate elevation of 320 feet Above Mean Sea Level

(AMSL). More detailed information about the location of the subject project is presented on

Figures A-1 and A-2 within Appendix A of this report.

3. SCOPE OF SERVICES

Our scope of services for this project included the followings:


Performing a site reconnaissance, evaluating the general site conditions, and marking the

proposed boring locations for the purpose of underground utility clearance;

Conducting four exploratory borings at the proposed locations within vicinity of the project

limits using asphalt concrete coring machine and hand auger, and sampling periodically;

Measuring the existing asphalt concrete and base sections thicknesses;

Performing laboratory testing on selected soil samples obtained from our exploratory

borings;

Reviewing the field data and the laboratory test results, performing engineering analyses,

and preparing a final geotechnical evaluation report for the site which includes our findings

and recommendations for the design and rehabilitation of the distresses from the

geotechnical point of view.

4. FIELD EXPLORATORY WORKS

The field exploration program took place on November 7, 2017 and it consisted of performing a

total of four 6-inch diameter exploratory borings. Figure A-2 presents approximate locations of

the conducted borings plotted on the aerial photo of the intersection along with the pavement

distresses limits. Borings B-1 and B-2 were placed near the shoving/rutting areas, Boring B-3 near

the corner depression, and Boring B-4 near the center depression.

The borings were conducted using an asphalt concrete coring machine and hand auger, were drilled

down to the planned depth. Modified California Sampler samples were taken periodically for the

deeper borings. Borings B-1 and B-2 were drilled down to approximately 2 feet below the ground

surface (bgs), while Boring B-3 and B-4 were drilled down to approximately 6 feet and 7 feet bgs,

respectively. The thicknesses of the asphalt concrete (AC) and underlaying base layer were

measured. The following table presents the results of our measurements on the existing pavement

sections along with classification of base and subgrade material.


Table 1 – Field Measurement of Asphalt Concrete and Base Layer Thicknesses

SAMPLE LOCATION

LAYER THICKNESSES (IN) MATERIAL CLASSIFICATION

ASPHALT CONCRETE BASE BASE(1) SUBGRADE(2)

B-1 7.5 9.5 Crushed Aggregate Base Silty Sand




Notes: (1) Base classification was based on visual observation, and was not tested for its conformity to

specification defined the Standard Specifications for Public Works Construction (“Greenbook”). (2) Subgrade classification was based on visual classification method with the aids of laboratory lab

tests.

5. SUBSURFACE CONDITIONS

The soil encountered in our exploratory work was predominantly silty sands with varying amounts

of gravel. The silty sand layers in Boring B-3 is medium dense throughout, whereas in Boring B-

4 is in very loose to loose in the upper 6 feet below the ground surface (bgs) and becoming medium

dense below 6 feet bgs. The encountered soils in Boring B-3 were generally slightly moist to moist,

whereas Boring B-4 were moist to very moist in the upper 5 feet bgs and slightly moist to moist

below 5 feet bgs. It should also be noted that the material in Boring B-1 had a black appearance

whereas the other three borings had a brown appearance.

Variations in the soil layer conditions, as well as more detailed information, are indicated on the

attached Boring Logs in Appendix B. Approximate locations of the borings are shown on the

boring locations plan, Figure A-2. The soil conditions described in this report are based on the

soils observed in the test borings drilled for this investigation and the laboratory test results. It is

possible that soil conditions could vary in areas other than the boring locations.

6. LABORATORY TESTING

Laboratory testing, including moisture content, unit weight, gradation, and plasticity index

(Atterberg limits) tests were performed on selected soil samples obtained from the site

investigation to aid in the classification of the encountered layers and to evaluate their engineering

properties. Consolidation tests been conducted on selected soil samples to determine their collapse


potential. Also, bitumen extraction and sieve analyses have been conducted on the upper asphalt

concrete section for one of the asphalt concrete cores obtained. The results of our laboratory tests

are presented on the boring logs in Appendix B, as well as within Appendix C.

7. GROUNDWATER

As mentioned above, the subject site has an approximate elevation of about 320 feet Above Mean

Sea Level (AMSL). We have reviewed the historically highest groundwater contour map shown

in “Seismic Hazard Zone Report for the El Monte 7.5-Minute Quadrangle, Seismic Hazard Zone

Report 024” published by “Department of Conservation, California Division of Mine and

Geology", shown in Figure D-1 within Appendix D. Historically highest groundwater depth is at

approximately 35 feet bgs. Also, groundwater was not encountered to a maximum depth of 7.4

feet bgs during our exploratory works (Appendix B). Based on the site topography, historically

highest groundwater contour map, and data obtained from the exploratory borings conducted at

the site, it is unlikely that the groundwater would contribute to the pavement distresses observed.

8. COLLAPSE POTENTIAL

To study the hydro-consolidation (“collapse”) characteristics of the site’s underlaying soil, we

have performed three consolidation tests on selected samples where inundation occurred at vertical

stresses close to their corresponding in-situ stresses. The silty sand in Boring B-3 at 24 inches bgs

settled approximately 5.0 percent upon inundation at a vertical stress of about 400 psf. The silty

sand in Boring B-4 at 24 inches and 65 inches had negligible settlement upon inundation. Due to

the moderate collapse potential for slightly moist sample, care shall be taken to ensure all backfill

are moisture-condition above their optimum moisture content.

9. CONCLUSIONS AND RECOMMENDATIONS

9.1. Discussion

Based on the manholes observed at the site and the provided utility plans, there is a sewer line at

approximately 8 to 10 feet below the ground surface (bgs). The center depression is located

between two manholes, i.e. right above the sewer line. However, based on the trend of change in


moisture content in Boring B-4, it cannot be concluded that any leak or a broken sewer line was

the cause of the center depression. The excess moisture in the upper 5 feet indicates that it could

be a surface runoff issue that contributed to the initial softening of the subgrade soil, or that the

center depression has caused excess water to accumulate in that area and infiltrate into the subgrade

soil. It is noted that the soils in the upper 6 feet adjacent to the center depression was in very loose

to loose state, thus contributing to the settlements seen.

The soils adjacent to the corner depression was medium dense throughout with a slight increase in

moisture with increasing depth. It is not clear what is the cause for the corner depression since it

does not have a loose soil layer nor excess moisture content. However, it is noted that the

depression is right above a conduit for telecom cables (Photo 2) and further investigation should

be performed by the responsible telecom company.

The effect of hydro-consolidation (“collapse”) as mentioned in Section 8 should also be

considered. Surface runoff with poor drainage could infiltrate through the pavement section and

into the subgrade soils, causing a trigger of collapse. The high moisture content seen in Boring B-

4 could indicate that collapse had already been triggered and resulted in the center depression.

Shoving at the edge of the concrete bus pad indicates that there could be too much asphalt binder,

too much fine aggregate, rounded aggregate, etc. Also, various mechanical parts and tools were

observed to be pressed into the asphalt near Boring B-1 (Photo 6). These clues help reinforce that

the asphalt mix could be an issue. However, the scope of our investigative works cannot determine

the existence of such problem.

9.2. Recommended Rehabilitation

The cause of the center and corner depression is most likely from lack of adequate compaction on

backfilled materials placed in the trenches during construction of the existing utility lines. Also,

volume change in the soils due to intrusion of water from any source (e.g. runoff) and existence of

collapsible materials could have exacerbated the situation. To mitigate the depression and prevent

future progress of settlement, the area should be rehabilitated by Full Depth Removal and

Reconstruction (FDRR). The FDRR should be either performed along the entire length of the sewer

line and telecom trench within the intersection, or within the locality of the distressed.

If localized repair is intended, the limit of excavation and removal of the soils shall extend laterally a

distance equal to the diameter of the depression on all sides (i.e. if the average diameter of the


depression is 3 feet, the FDRR area should be approximately 9 feet by 9 feet). After the entire

backfilled materials are excavated, the removed soils shall be placed back in layers not exceeding 8

inches in thickness when placed loose, and shall be moisture-conditioned to a moisture content

between the optimum and 3 percent above the optimum moisture content, and compacted to at

least 90 percent of the maximum dry density obtained per ASTM D1557. Prior to placement of

backfill, the bottom of removal shall be observed and confirmed to be competent by the

Geotechnical Engineer of Record.

Also, as discussed, the asphalt pavement at the intersection has demonstrated significant deformations

of shoving and rutting types. It is our recommendation that the asphalt pavement within the

intersection and at least 150 feet before the intersection from each side, be demolished and replaced

with a new pavement section/FDRR. The recommended sections for FDRR of the pavement section

are provided in the following section 9.2.1.

Samples of the subgrade soils were obtained from our exploratory works and assumed R-Value was

chosen based on the subgrade soil classification. The pavement section recommendations provided in

Table 2 below are based on the R-Values assumed. The pavement section recommendations are for

Traffic Index (TI) values of 9, 10 and 11. We would be pleased to provide additional pavement section

recommendations for different TI values upon request.

9.2.1. Full Depth Removal and Reconstruction (FDRR)

The Full Depth Removal and Reconstruction (FDRR) alternative includes removal of the entire

asphalt concrete and base layer, reworking and compacting of the subgrade soils, and placing back

well-compacted layers of base and asphalt concrete.

This alternative consists of constructing the pavement section by placing layers of hot Asphalt

Concrete Mix (ACM) over the compacted base materials. The base layer should be underlain by

compacted subgrade soils. It is recommended that the upper 12 inches of the subgrade soils below the

base layer be scarified, moisture-conditioned, and compacted. The subgrade soils shall be moisture-

conditioned to moisture content between the optimum and 2 percent above the optimum moisture

content, and compacted to at least 95 percent of the maximum dry density obtained per ASTM D1557.

For the rehabilitation within the center depression area, it is recommended that the additional subgrade

soils be reworked up to 5 feet below the ground surface.


Asphalt thickness for different TI values are provided in Table 2. It is recommended that the first

layer of ACM over the base material should be a dense/leveling course of about 2 inches thick,

overlaid by placing of layer(s) of ACM with maximum thickness of 4 inches each layer.

Table 2 – Recommended Full Depth Removal and Reconstruction

R-Values TRAFFIC INDEX MINIMUM COURSE THICKNESS (IN)

HOT MIXED ASPHALT, tAC AGGREGATE BASE, tB

40

9 6.0 9.0

10 6.5 10.5

11 7.0 12.0

Base course material should consist of Crushed Aggregate Base (CAB) as defined by Section 200-

2.2 of the Standard Specifications for Public Works Construction (“Greenbook”). In lieu of CAB

materials, Crushed Miscellaneous Base (CMB) materials as defined by Section 200-2.4 of the

Greenbook may be used. Base course should be compacted to at least 95 percent of the maximum dry

density of that material. The assumed R-value in design of the above provided preliminary sections

for CAB material is 78.

Base course material should be purchased from a supplier who will certify the base course will meet

or exceed the specifications in the Greenbook as indicated. We could, at your request, perform sieve

analysis and sand equivalency tests on material delivered to the site which appears suspect.

Additional tests could be performed, upon request, to determine if the material is in compliance with

the specifications.

9.3. Utility Trench Backfilling

If utility trenches are encountered during reworking of the deep subgrade for the center depression

or corner depression, recommendation shall be as followed. A minimum of 4 inches of bedding

material shall be first placed below the bottom of the utility line, on a firm and unyielding subgrade.

Bedding material shall also be placed immediately around a utility line extending to a point 12

inches above the top of the line. The bedding material should consist of sand, fine-grained gravel,

or cement slurry to support the line and protect it. The bedding material should meet the

specification given in the latest edition of the Greenbook. Sand or gravel should be compacted in

accordance with Greenbook specifications.


Above the bedding material and up to the finished ground surface, utility trench backfills may

consist of low-expansive material (EI less than 35), and should be mechanically compacted to at

least 90 percent of the maximum dry density of the soils, except below pavements or within the

areas with a higher relative compaction such as building pads. A minimum relative compaction of

95 percent will be required in the upper 1 foot of the backfill underneath the pavement areas and

the minimum required relative compaction for the upper 2 feet within the building pads shall be

as set forth for the building pads. Prior to backfilling, the gradation and expansivity of the backfill

material shall be tested, reviewed, and approved by the soils engineer. The bedding materials and

backfilling should be placed in accordance with Sections 306-1.2.1 and 306-1.3 of the Greenbook.

When adjacent to any footings, utility trenches and pipes should be located above an imaginary

line measured at a gradient of 1:1 (horizontal: vertical) projected down from the bottom edges of

any footings. Otherwise the pipe should be designed to accept the lateral effect from the footing

load, or the footing bottom should be deepened as needed to comply with this requirement, into

competent materials.

For bedding and backfilling of trenches and upon approval of the soils engineer, slurry mix

(CLSM) may be used. The slurry mix shall comply with the requirements of Section 201-6 of the

Greenbook. The backfill material shall be observed, tested and approved by the Geotechnical

Engineer.

9.4. Temporary Excavations

Based on the grading recommendations provided, it is expected that the excavation for reworking

the subgrade be as deep as about 5 feet bgs. The shallow soils at the site are expected to be

temporarily stable when excavated at a gradient of 1.5:1 (H:V) for excavations that are less than 5

feet in height. The top of slopes should be barricaded to prevent vehicles and storage loads within

7 feet of the tops of the slopes. A greater setback may be necessary when considering heavy

vehicles (e.g. concrete trucks and cranes) and we should be advised of such heavy vehicle loadings

so that specific setback requirements can be established. When excavating adjacent to footings of

existing buildings, proper means should be employed to prevent any possible damage to the

existing structures. Adjacent to existing buildings, un-shored excavations should not extend below

a 1:1 (H:V) plane extending downward from the lower edge of adjacent footings. All regulations

of State or Federal OSHA should be followed.


Temporary excavations are assumed to be those that will remain un-shored for a period of time

not exceeding 10 days. In dry weather, the excavation slopes should be kept slightly moist, but not

saturated. If excavations are made during the rainy season (normally from November through

April), particular care should be taken to protect slopes against erosion. Mitigative measures, such

as installation of berms, plastic sheeting, or other devices, may be warranted to prevent surface

water from flowing over or ponding at the top of excavations.

10. OBSERVATION AND TESTING

This final report has been prepared assuming that GEO-ADVANTEC, INC. will perform all

geotechnical-related field observations and testing. If the recommendations presented in this report

are utilized, and observation of the geotechnical work is performed by others, the party performing

the observations must review this report and assume responsibility for recommendations contained

herein. That party would then assume the title “Geotechnical Consultant of Record”.

A representative of the Geotechnical Consultant should be present to observe all grading

operations as well as all footing excavations. Upon the client’s request, a report or final verification

letter presenting the results of these observations and related testing should be issued upon

completion of the grading operations.

11. CLOSURE

The findings and recommendations presented in this final report were based on the results of our

field and laboratory investigations, combined with professional engineering experience and

judgment. The report was prepared in accordance with generally accepted engineering principles

and practice. We make no other warranty, either expressed or implied.

The soils encountered in the boreholes are believed to be representative of the total under

consideration area for the subject proposed developments; however, soil characteristics can vary

throughout the site. GAI should be notified if subsurface conditions are encountered which differ

from those described in this report.


Samples secured for this investigation will be retained in our laboratory for a period of 45 days

from the date of this report and will be disposed after this period unless other arrangements are

made.

Should you have any questions concerning this submittal, or the recommendations contained

herewith, please do not hesitate to call our office.

Respectfully submitted, GEO-ADVANTEC, INC. Giang (Jack) Lee, P.E. Shawn Ariannia, Ph.D., P.E., G.E. Senior Project Engineer Principal Geotechnical Engineer Distribution:

1. Addressee (2 wet stamped copy + pdf copy via e-mail) 2. File

19

APPENDICES

Appendix A: Maps and Plans and Figures Figure A-1: Vicinity Map Figure A-2: Boring Locations Plan

Appendix B: Field Exploratory Logs Keys to Logs Borings B-1 to B-4

Appendix C: Laboratory Test Results

Sieve Analysis Percent Finer than No. 200 Consolidation Test Asphalt Binder/Extraction Test

Appendix D: Quadrangle Maps

Figure D-1: Historically Highest Groundwater Map

Appendix P: Site Photographs

APPENDICES

APPENDIX A MAPS, PLANS AND FIGURES

APPENDIX B FIELD EXPLORATORY BORING LOGS

SPT CD (2) SPT CD (1) CD (2)0-4 0-8 0-4 0-8 0-20

5-8 9-16 5-10 9-18 21-50

9-15 17-45 11-30 19-54 51-150

16-30 46-195 31-50 55-90 151-250

over 30 over 195 over 50 over 90 over 250

SOME

GRANULAR SOILS(SANDS, GRAVELS, etc.)

*THE FOLLOWING "DESCRIPTIVE TERMINOLOGY/ RANGES OF MOISTURE CONTENTS" HAVE BEEN USED FOR MOISTURE CLASSIFICATION IN THE LOGS.

DESCRIPTION

AND

20-35%

DESCRIPTIVE ADJECTIVE VS. PERCENTAGEDESCRIPTIVE ADJECTIVE

TRACE

LITTLE

PERCENTAGE REQUIREMENT

1 - 10%

10-20%

VERY DENSEHARD over 39

* CONVERSION BETWEEN CALIFORNIA DRIVE SAMPLERS (CD) AND STANDARD PENETRATION TEST (SPT) BLOW COUNT HAS BEEN CALCULATED USING "FOUNDATION ENGINEERING HAND BOOK" BY H.Y. FANG. (VALUES GIVEN AS CD (1) ARE FOR 140 Lbs HAMMER WEIGHT AND 30 INCHES DROP ONLY. VALUES GIVEN AS CD (2) ARE FOR HAND AUGERING WITH 35 Lbs HAMMER WEIGHT AND 18 INCHES FREE DROP/FALL. )

LOOSE

MEDIUM DENSE

DENSEVERY STIFF 19-39

FIRM 5-9

STIFF 10-18

0-4 VERY LOOSE

CONSISTENCY

GRANULAR SOILS (SANDS, GRAVELS, etc.)

RELATIVE DENSITY *BLOWS/FOOTFINE-GRAINED SOILS (SILTS, CLAYS, etc.)

*BLOWS/FOOT

KEY TO LOGS

MOIST 10-13

MOISTURE CONTENT (%)

DRY 2 - 4

SLIGHTLY MOIST

<10

15-24

24-28

35-50%

FINE-GRAINED SOILS(SILTS, CLAYS, etc.)

SPT/CD BLOW COUNTS VS. CONSISTENCY/DENSITY

CD (1)SOFT

Almost saturated; visible free water

APPROXIMATE MOISTURE CONTENT DEFINITION

Dry to the touch; no observable moistureSome moisture but still a dry appearance

Damp, but no visible water

Enough moisture to wet the hands

WET 20-25

VERY MOIST 15-20

6-8

DEFINITION

30-38

>40

APPENDIX C LABORATORY TEST RESULTS

APPENDIX D QUADRANGLE MAP

APPENDIX P SITE PHOTOGRAPHS

limited pavement/geotechnical investigation report

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