geo technical exploration report
TRANSCRIPT
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THIELE GEOTECH, INC.13478 Chandler Road
Omaha , Nebraska 68138-3716
402.556.2171 Fax 402.556.7831
www.thielegeotech.com
G EO TEC H N I C A L M A TERI A L EN V I R O N M EN TA L EN G I N E ERI N G
Geotechnical Exploration Report
Pump Station
Railroad Street and Herbert StreetBeatrice, Nebraska
Prepared for:WLA Consulting, Inc.1640 L Street, Suite DLincoln, Nebraska 68508
March 9, 2010
TG Project No. 10026.00
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Geotechnical Exploration Report
Pump Station
Table of Contents
INTRODUCTION ................................................................................................................................................. 1PROJ ECT DESCRIPTION .................................................................................................................................. 2SURFACE AND SUBSURFACE CONDITIONS ............................................................................................... 3
SITE CONDITIONS ............................................................................................................................................................ 3LOCAL GEOLOGY ............................................................................................................................................................ 3SOIL CONDITIONS ........................................................................................................................................................... 3GROUND WATER OBSERVATIONS .............................................................................................................................. 4
ANALYSIS AND RECOMMENDATIONS ........................................................................................................ 5GENERAL ........................................................................................................................................................................... 5EXCAVATION DEWATERING ........................................................................................................................................ 5SHORING ............................................................................................................................................................................ 5PUMP STATION ................................................................................................................................................................. 6EARTHWORK AND EXCAVATIONS ............................................................................................................................. 7OTHER RECOMMENDATIONS ....................................................................................................................................... 7
APPENDIX
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INTRODUCTION
Thiele Geotech, Inc. has completed a geotechnical exploration study for the proposed pump station to
be located near Railroad Street and Herbert Street in Beatrice, Nebraska. The purpose of this study
was to identify the general soil and ground water conditions underlying the site, to evaluate
engineering properties of the existing soils, to provide earthwork and site preparation
recommendations, and to recommend design criteria and parameters for foundations and other earth
supported improvements.
This study included soil borings, laboratory testing, and engineering analysis. One test boring was
drilled at the location of the new pump station. The field and laboratory data are presented in the
Appendix, along with a description of investigative methods.
The drilling and testing performed for this study were conducted solely for geotechnical analysis. No
analytical testing or environmental assessment has been conducted. Any statements or observations in
this report regarding odors, discoloration, or suspicious conditions are strictly for the information of
our client. If an evaluation of environmental conditions is desired, a separate environmental
assessment should be conducted. This study did not include biological assessment (e.g. mold, fungi,
bacteria) or evaluation of measures for their control.
It should also be noted that this report was prepared for design purposes only, and may not be
sufficient for a contractor in bid preparation. Prospective contractors should evaluate potential
construction problems on the basis of their own knowledge and experience in the local area and on
similar projects, taking into account their own intended construction methods and procedures.
This report is an instrument of service prepared for use by our client on this specific project. The
report may be duplicated as necessary and distributed to those directly associated with this project,
including members of the design team and prospective contractors. However, the technical approach
and report format shall be considered proprietary and confidential, and this report may not be
distributed in whole or in part to any third party not directly associated with this project. By using and
relying on this report, all other parties agree to the same terms, conditions, and limitations to which the
client has agreed.
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PROJECT DESCRIPTION
The project consists of a 28-foot deep wet well for a new pump station. We assume that the structure
will consist of reinforced concrete floors, walls, and top. The new pump station will be located
adjacent to an existing pump station near the intersection of Railroad Street and Herbert Street in
Beatrice, Nebraska. The site is located on the north bank of Indian Creek on the east side of Railroad
Street.
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SURFACE AND SUBSURFACE CONDITIONS
SITE CONDITIONS
The project site is located north of Railroad Street and east of Herbert Street, immediately north ofIndian Creek in Beatrice, Nebraska. The pump station site is built up by several feet. The site is in an
open area which is grass and tree covered.
LOCAL GEOLOGY
The surface geology of eastern Nebraska is Pleistocene in age and consists of eolian (wind-blown)
deposits of Peoria and Loveland loess. The loess formed in dune-shaped hills west of the Missouri
River. The Peoria loess typically consists of silty lean clays that are stiff when dry but become softer
with increasing moisture content. The Peoria often exhibits low unit weight and is collapse
susceptible. The Loveland loess is an older deposit, and typically consists of lean clays. TheLoveland generally exhibits higher unit weights and shear strengths than the Peoria.
The loess overlies Pleistocene glacial deposits of Kansan and Nebraskan till. The till consists of lean
to fat clays mixed with sand, gravel, and occasional cobbles. The glacial deposits are generally fairly
deep, but are sometimes near the surface at lower elevations on steep slopes. Cretaceous sandstone or
Pennsylvanian limestone and shale form the bedrock unit below the glacial deposits. The depth to
bedrock is normally great, and rock is rarely encountered in construction.
Along drainageways, alluvial and colluvial deposits are typically present. These soils were formed by
erosion of the adjoining loess-mantled hills. Alluvial deposits are generally present along creeks andin major drainageways. The upper several feet of alluvium are usually stiffer due to the effects of
desiccation. Colluvial soils are usually located at the base of steep slopes and in upland draws, and are
formed by local creep and sloughing.
SOIL CONDITIONS
The soils encountered in the test borings generally consisted of man-placed fill over alluvium.
Man-placed fill was encountered in the upper 7 feet of the boring. It was described as dark gray,
moist, hard lean clay. Based on an assumed Standard Proctor the fill had compaction levels of roughly
100 percent.
Alluvium was encountered below the fill, and extended to a 28 foot depth. It was described as light
brown to reddish brown, slightly moist to wet, loose, poorly-graded sand.
Shale and limestone rock was encountered at 28 feet below grade. It was described as light brown,
wet, and very hard in consistency. Drilling refusal was encountered at 30 feet, where a Standard
Penetration Test blow count of 50 for 2 inches of penetration was recorded.
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Ranges of engineering properties from laboratory tests on selected samples are presented in Table 1.
Table 1 - Laboratory Results
Soil Layer
Moisture
Content (%)
Dry Unit
Weight (pcf)
Unconfin
edCompressive
Strength(tsf)
Classification (LL/PI)
Man-placed fill 17 to 18 103 to 111 2.3 CL (36/20)
Alluvium 2 to 15 -- -- SP (P-200=4.3%)
GROUND WATER OBSERVATIONS
Ground water levels were observed in the borings as presented in Table 2. Note that ground water
levels may fluctuate due to seasonal variations and other factors.
Table 2 - Water Level Observations
Boring
Number
Water Level (ft. below grade)
During Drilling End of Drilling
B-1 15.0 15.0
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ANALYSIS AND RECOMMENDATIONS
GENERAL
The soils encountered in the test boring were variable with depth. Soil in the upper 7 feet consistedof lean clay which was hard in consistency. Below the lean clay fill, alluvial poorly-graded sand was
encountered to a 28 foot depth. Shale and limestone rock was found at 28 feet. The rock was very
hard at 30 feet. Excavation into the rock will likely require pneumatic or hydraulic rock breakers.
Ground water was fairly shallow in the boring, and dewatering will be a major consideration in
making the excavation to construct the pump station.
EXCAVATION DEWATERING
Ground water was present at roughly 15 feet below existing grade. The proposed excavations extend
below the water table and will require dewatering to facilitate construction.
Soils encountered below the water table consist predominantly of poorly-graded sand. Since the soils
beneath the water table are mainly sand, we expect seepage rates to be high. Sump pumps will not be
sufficient to control the inflow of water into excavations. A well point or deep well system will be
necessary to adequately dewater the excavations. We expect that multiple dewatering points will be
necessary around the excavation to maintain a stable bottom condition.
SHORING
OSHAs Construction Standards for Excavations require that the contractors excavation activitiesfollow certain worker safety procedures. These include a requirement that excavations over 4 feet
deep be sloped back, shored, or shielded. The soils encountered in the test borings generally classify
as type B and C soils according to the OSHA standard. The maximum allowable slope for an
unbraced excavation in these soils is 1H:1V and 1.5H:1V, respectively, although other provisions and
restrictions apply. Excavations over 20 feet deep require specific design by a licensed Professional
Engineer. The contractor is solely responsible for site/excavation safety and compliance with OSHA
regulations. The geotechnical engineer assumes no responsibility for site safety, and the above
information is provided only for consideration by the designers.
For braced excavation design, we recommend using a cohesion of 1,000 psf where clay is
encountered, and a friction angle of 30 degrees where sand is present. A soil unit weight of 120 pcf is
recommended above the water table, and buoyant unit weight of 65 pcf is recommended below the
water table. Dewatering will have a significant impact on shoring loads. The shoring design should
carefully consider water levels, hydrostatic loads, and dewatering requirements.
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PUMP STATION
The structure is planned for a 28-foot depth, which puts it very close to the rock layer at 28 to 30
feet. We recommend extending the foundation to bear on the hard rock at roughly 30 feet below grade
instead of bearing on a thin layer of sand at 28 feet. The following paragraphs include discussion
about bearing on sand in case the structure becomes shallower than originally planned.
The allowable bearing pressure for a buried structure would be the gross bearing pressure, which is the
net allowable bearing pressure derived from the shear strength of the soil plus the surrounding
overburden pressure. During construction, the net allowable bearing pressure controls before the
structure is backfilled. Thus, we recommend that both the construction case and long-term case be
considered in sizing the mat foundation for the structure.
The net allowable bearing pressure for the saturated sand would be approximately 1,000 psf. The
overburden pressure at a depth of 28 feet would be approximately 1,820 psf, based on a soil unit
weight of 65 pcf and assuming the water table at the ground surface. Thus, the gross allowablebearing pressure for the lift station bearing on sand would be approximately 2,820 psf. A conservative
net allowable bearing pressure for the hard rock would be approximately 5,000 psf. The overburden
pressure at a depth of 30 feet would be approximately 1,950 psf, based on a soil unit weight of 65 pcf
and assuming the water table at the ground surface. Thus, the gross allowable bearing pressure for the
lift station bearing on rock would be approximately 6,950 psf. The actual contact pressure should be
calculated by dividing the maximum operating weight of the lift station structure across the outside
diameter of the lift station walls. Any footing projection outside of the walls should be neglected in
the gross bearing calculation due to the balancing overburden pressure above this section of the
foundation. For structural design of the base, this contact pressure should be uniformly distributedacross the interior slab as a conservative practice. The same contact pressure should be separately
applied to the footing projection as a cantilever. In addition, the footing projection should be designed
to support the full weight of the overlying soil acting downward to resist buoyant effects.
Since the net contact pressure for the completed/backfilled structure is actually negative, resulting in a
reduction in the effective stress below the structure, there should be minimal settlement due to
compression of the underlying soil. Actual settlement will be a function of the installation process, but
should be minor (less than 1 inch if supported on sand, and negligible if supported on rock) if the
contractor can maintain a stable excavation. If the bottom of the excavation ends in sand, we
recommend placing a layer of crushed rock below the base to provide a stable work platform. This
layer should be 12 inches thick, consisting of a 6-inch thick layer of 3-inch stabilization rock and a 6-
inch thick layer of pipe bedding material. A lean concrete mix may be placed as a mud slab in lieu of
the bedding layer for construction convenience.
For uplift design, we recommend that the design ground water level be taken at the ground surface.
The uplift resistance should be calculated as the minimum operating weight of the lift station structure
plus the effective weight of the soil mass above the footing projection outside of the barrel section.
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An effective unit weight of 65 pcf should be used for the backfill soil above the footing projection.
The hydrostatic pressure and resisting loads should also be applied across the bottom of the structure
to check the structural capacity of the base slab under this loading condition.
For evaluating lateral pressures on the barrel section, we also recommend using the design ground
water level at the ground surface. Lateral loads on the walls should be calculated at 30 pcf (equivalent
fluid) for the effective soil pressure (at rest condition) plus full hydrostatic pressure.
EARTHWORK AND EXCAVATIONS
The excavated site soils will generally be suitable for reuse as structural fill, although significant
moisture conditioning may be required. Any off-site borrow should be a clean, inorganic silt or lean
clay with a liquid limit less than 45 and a plasticity index less than 20, or poorly-graded sand similar to
the on-site soil. Borrow material should not contain an appreciable amount of roots, rock, or debris,
and should not contain any foreign material with a dimension greater than 3 inches.
All fills and backfill around the structure should be placed and compacted as structural fill. Fill should
be placed in thin lifts not to exceed 8 inches loose thickness. Structural fill should be compacted with
a sheepsfoot type roller to a minimum of 95 percent of the maximum dry density (ASTM D698,
Standard Proctor). Moisture content should be controlled to between -3 and +4 percent of optimum.
Quality control testing is an important part of any earthwork operation. It is recommended that a
representative of the geotechnical engineer periodically monitor earthwork operations to verify proper
compliance with these recommendations, including compaction levels.
OTHER RECOMMENDATIONS
During detailed design, additional issues may arise and possible conflicts may occur with our
recommendations. Such issues and conflicts should be resolved through dialogue between the
geotechnical engineer and designers. It is recommended that the geotechnical engineer review the
final design, including the plans and specifications, to verify that our recommendations are properly
interpreted and incorporated into the design.
If any changes are made in the design of the project, including the nature or location of proposed
facilities on the site or significant elevation changes, the analysis and recommendations of this report
shall not be considered valid unless the changes are reviewed. The analysis and recommendations ofthis report should not be applied to different projects on the same site or to similar projects on different
sites.
The analysis and recommendations in this report are based upon borings at specific locations. The
nature and extent of variation between boring locations is impossible to predict. Because of this,
geotechnical recommendations are preliminary until they have been confirmed through observation of
site excavation and earthwork preparation. If variations appear during subsequent exploration or
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during construction, we may reevaluate our recommendations and modify them, if appropriate. The
geotechnical engineer should be retained during construction to observe compliance with the
recommendations of this report and to provide quality control testing of earthwork construction. If
these services are provided by others, including the contractor, the entity that provides construction
phase observation and testing shares responsibility as the geotechnical engineer of record forimplementing or modifying these recommendations.
Respectfully submitted,Thiele Geotech, Inc.
Prepared by,
John A. Christiansen, P.E.Nebraska License E-7821
P:\10026.00\GEOTECHNICAL EXPLORATION REPORT.DOC
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T h i e l e G e o t e c h I n c
APPENDIX
Subsurface Exploration Methods
Legend of Terms
Boring Location Plan
Boring Logs
Soil Test Summary
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SUBSURFACE EXPLORATION METHODS
The fieldwork for this study was completed on February 15, 2010. The exploratory program consisted
of 1 test boring drilled at the approximate location shown on the Boring Location Plan. Boring
locations were selected to provide the desired site coverage and were adjusted to accommodate access
conditions. The boring location was laid out by estimating angles and measuring with a cloth tape
from existing site features. The boring location should only be considered accurate to the degree
implied by the methods used to define them.
The test boring was advanced using hollow stem augers powered by a truck-mounted drill rig. Soil
samples were obtained at selected depths as indicated on the boring logs. A 3-inch nominal diameter
thin-walled sampler was hydraulically pushed to obtain undisturbed samples. Disturbed samples were
obtained by driving a 2-inch nominal diameter split barrel sampler while conducting standard
penetration tests (SPT).
The boring log was prepared based on visual classification of the samples and drill cuttings, and by
observation of the drilling characteristics of the subsurface formations. The log was supplemented and
modified based on the laboratory test results and further examination of the recovered samples. The
stratification lines on the boring log represent the approximate boundary between soil types, but the
insitu transition may be gradual.
Water level observations were made at the times stated on the boring log. The boring was backfilled
with drill cuttings at the completion of the fieldwork.
The field boring logs were reviewed to outline the depths, thicknesses, and extent of the soil strata. A
laboratory testing program was then developed to further classify the basic soils and to evaluate the
engineering properties for use in our analysis.
Laboratory tests to further classify the soils included visual classification, moisture content, dry unit
weight, Atterberg limits, and fraction passing the #200 sieve. The shear strengths of cohesive samples
were evaluated using the unconfined compression test.
The boring log and related information in this report are indicators of subsurface conditions only at the
specific locations and times noted. Subsurface conditions, including ground water levels, at other
locations of the site may differ significantly from conditions that exist at the sampling locations. Also
note that the passage of time may affect conditions at the sampling locations.
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LEGEND OF TERMSSoil Description Terms
Consistency - Fine Grained Consistency - Coarse Grained Moisture Conditions
Very Soft, Soft, Firm, Very Loose, Loose, Medium Dry, Slightly Moist, Moist
Hard, Very Hard Dense, Dense, Very Dense Very Moist, Wet (Saturated)
Sample Identification Sample Type Sample Data Laboratory Data
U -- Undisturbed (Shelby Tube) No. -- Number MC -- Moisture contentS -- Split barrel (disturbed) SPT -- Standard penetration test d -- Dry unit weight
C -- Continuous sample bpf -- blows per foot qu -- Unconfined compression
A -- Auger cuttings (disturbed) Rec -- Recovery LL/PI -- Liquid limit & plasticity index
Unified Soil Classification System Peat Pt Highly organic soils
Fat Clay CH Clay - Liquid Limit >50 * 50% or more
Elastic Silt MH Silt - Liquid Limit >50 * smaller than
Lean Clay CL Clay - Liquid Limit % sand
Poorly-Graded Gravel GP Gravels with less than 5 percentWell-Graded Gravel ** GW smaller than No. 200 sieve *
* See Plasticity Chart for definition of silts and clays ** See Criteria for Sands and Gravels for definition of well-graded
Plasticity Chart
Pl
as
tic
ity
In
d
e
x
60
50 CH or OH
40
30MH or OH
20 CL or OL
10CL-ML ML
0 10 20 30 40 50 60 70 80 90 100
L i q u i d L i m i t
Criteria for Sands and Gravels Coarse Fine Coarse Medium Fine FINES
Boulders Cobbles Gravel Gravel Sand Sand Sand (silt or clay)
Sieve size 10" 3" " #4 #10 #40 #200
Well-graded sands (SW) Cu=D60/D106 and Cc=(D30)2/(D10 x D60) 3 and 1
Well-graded gravels (GW) Cu=D60/D104 and Cc=(D30)2/(D10 x D60) 3 and 1
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WAT
D
E
DEP(ft.)
bori
5
10
15
20
25
ER LEVEL OB
uring Drilling
nd of Drilling
COLOR M
ng backfilled
darkgray
light slibrown
grayishbrown
ERVATIONS
VIS
IST. CONSI
15.0
15.0
ith cuttings
oist hard
htly loosoist
et
LO
AL/MANUAL
T.SOILTYPE
Railroad St
see B
lean clay
poorlygradedsand
PROJECT
LOCATION
ATION OF BO
ESCRIPTION
GEOLOGICORIGIN
Pump Statio
& Herbert St,
oring Locatio
fill
alluvium
ING
REMA
eatrice, NE
n Plan
light bmottl
fine tosa
minor fin
DRILLER
DRILLI
TYPE O
S
RKSNTY
Epley
3.2
g
U
rown Uling
oarse Ud
S
S
gravel
S
LOGGER
G METHOD
F SURFACE
AMPLE DATA
. &PE
SPT(bpf)
RE(in.
Kalbach
5 HSA
rass
-1 11
-2 11
-3 12
-4 3
-5 5
-6 5
BOJOB NO.
DRILL RI
ELEVATIO
LABORAT
)
MC(%)
d(pcf)
10026.0
CME 45
16.9 111.4
18.3 103.0
2.3
11.0
15.2
ING LDATE
BORING
N DEPT
ORY DATA
qu(tsf)
LL/PICLASS
0 2/15/1
B-1
30
LL=36
2.25 PI=20
CL
P200
4.3%
SP
D
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WAT
D
E
DEP(ft.)
bori
30
35
40
45
50
ER LEVEL OB
uring Drilling
nd of Drilling
COLOR M
ng backfilled
reddishbrown
lightbrown
ERVATIONS
VIS
IST. CONSI
15.0
15.0
ith cuttings
et loos
et veryhard
LO
AL/MANUAL
T.SOILTYPE
Railroad St
see B
poorlygradedsand
rock
PROJECT
LOCATION
ATION OF BO
ESCRIPTION
GEOLOGICORIGIN
Pump Statio
& Herbert St,
oring Locatio
alluvium
ING
REMA
eatrice, NE
n Plan
weathewith lim
bottom of h
DRILLER
DRILLI
TYPE O
S
RKSNTY
Epley
3.2
g
shaleestone S
ole @ 30
LOGGER
G METHOD
F SURFACE
AMPLE DATA
. &PE
SPT(bpf)
RE(in.
Kalbach
5 HSA
rass
-7 50/2
BOJOB NO.
DRILL RI
ELEVATIO
LABORAT
)
MC(%)
d(pcf)
10026.0
CME 45
ING LDATE
BORING
N DEPT
ORY DATA
qu(tsf)
LL/PICLASS
0 2/15/1
B-1(con
30
D
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SOIL TEST SUMMARProject J ob No.
Pump Station 10026.00Location Date
Railroad St & Herbert St, Beatrice, NEUNIT UNCONFINED SOIL CLASSIFICATION
BORING SAMPLE SAMPLE SAMPLE MOISTURE WEIGHT VOID SAT. COMPRESSION ATTERBERG PASS REMARK
NO. NO. DEPTH DIA. CONTENT WET DRY RATIO (%) qu STRAIN LIMITS #200
(ft.) (in.) (%) (pcf) (pcf) (e) (tsf) (%) LL PL PI (%)
B-1 U-1 1.5-3 16.9 130.2 111.4 0.512 89
U-2 3.5-5 2.85 18.3 121.8 103.0 0.636 78 2.25 4.7 36 16 20 CL
U-3 8.5-10 2.3
S-4 13.5-15 11.0
S-5 18.5-20 15.2 4.3 SP
S-6 23.5-25
S-7 28.5-30
2/22/2010