REPORT OF GEOTECHNICAL EXPLORATION
PEARL STREET - STORMWATER
EAST POINT, GEORGIA
FOR
CAMP DRESSER & MCKEE, INC.
OCTOBER 13, 2011
ECS PROJECT NO. 10:6178
REPORT OF GEOTECHNICAL EXPLORATION
PEARL STREET - STORMWATER
EAST POINT, GEORGIA
TABLE OF CONTENTS
INTRODUCTION
General
Project Information
FIELD EXPLORATION AND LABORATORY TESTING
PAGE
1
1
1
2
Subsurface Exploration
Laboratory Testing Program
2
3
SUBSURFACE CONDITIONS
3
Regional Geology
Soil Conditions
Groundwater Conditions
ANALYSIS AND RECOMMENDATIONS
Sewer Lines
Slopes / Trench Box
Fill Placement
Additional Considerations
CLOSING
APPENDIX
I.
II.
III.
Figure 1 - Site Vicinity Map
Figure 2 - Boring Location Plan
Unified Soil Classification System
Reference Notes for Boring Logs
Boring Logs (4)
Laboratory Testing Summary
ASFE Information about Geotechnical Reports
3
4
5
6
6
6
6
7
8
INTRODUCTION
General
This report presents the results of a geotechnical exploration for the Pearl Street - Stormwater
project in East Point, Georgia. Work was performed in general accordance with ECS Proposal
No. PAG-7318r2 as authorized by J.C. Lan with Camp Dresser & McKee, Inc. on August 29,
2011. Initially fieldwork was delayed while coordination with the city was performed to allow
access for the borings.
Project Information
This section is based on information provided and our site reconnaissance. The site is located
on the west side of Pearl Street in East Point, Georgia. A Site Vicinity Map is included in the
Appendix as Figure 1.
We understand the project consists of the replacement of an existing 8 inch sanitary sewer line and
the installation of a new 72 inch diameter storm sewer line. The length of the alignment is
approximately 1,000 feet. The existing sanitary sewer is about 18 feet below existing grade and
is planned to be replaced at the same approximate elevations. The new storm sewer is planned
for an invert about 10 feet below existing grade. The surface elevations range from 982 to 1038
feet across the site. The highest elevations are in the central portion of the site. The site
steeply slopes toward the north, south, and southwest.
At the time of fieldwork, the site was overgrown with thick underbrush. The western boundary of
the site was heavily wooded. A water and communications tower was located along the eastern
boundary of the site. A pond was located along the northern boundary of the site. The site was
bounded by Pearl Street to the east, Center Street to the south, residential properties to the
west, and residential properties and Center Park to the north.
The attached Boring Location Plan (Figure 2) presents the site development concept at the time
of this report. If any of the information presented is incorrect or has changed, please advise
ECS so that we may reevaluate our recommendations in the light of changes in the present
project concept.
Purposes of Exploration
The purposes of this exploration were to explore the soil and groundwater conditions at the site
and to develop engineering recommendations to guide design and construction of the proposed
project.
Pearl Street - Stormwater
ECS Project No. 10:6178
Page 2
We accomplished the purposes of the study by:
1.
Reviewing the available publications concerning local geology of the site and
performing a general site reconnaissance.
2.
Drilling borings to explore the subsurface soil and groundwater conditions.
3.
Performing laboratory tests on selected representative soil samples from the
borings to evaluate pertinent engineering properties.
4.
Evaluating the field and laboratory data to develop appropriate engineering
recommendations.
FIELD EXPLORATION AND LABORATORY TESTING
Subsurface Exploration
To explore the subsurface conditions at this site, a total of four (4) soil test borings were
performed along the proposed alignment. Borings B-1 through B-4 were performed to depths of
20 to 35 feet below existing grade. Borings B-1 and B-2 were extended due to unsuitable
materials encountered at proposed termination depths.
Boring locations were determined in the field by our representative who measured distances
and estimated right angles from existing site features. As these methods are not precise, the
boring locations shown on the attached Boring Location Plan (Figure 2) should be considered
approximate. Dozer clearing was used to access the boring locations.
The soil test borings were performed with an ATV mounted drill rig, which utilized hollow stem
augers to advance the boreholes. No water or drilling fluid was introduced during the process.
Representative soil samples were obtained by means of the split-barrel sampling procedure in
general accordance with ASTM Specification D-1586 with an automatic drive hammer. In this
procedure, a 2-inch O.D., split-barrel sampler is driven into the soil a distance of 18 inches by a
140-pound hammer falling 30 inches. The number of blows required to drive the sampler
through a 12-inch interval is termed the Standard Penetration Test (SPT) N-value and is
indicated for each sample on the boring logs. This value can be used as a qualitative indication
of the in-place relative density of cohesionless soils. In a less reliable way, it also indicates the
consistency of cohesive soils.
The drill crew maintained a field log of the soils encountered in the borings. After recovery,
each sample was removed from the sampler and visually classified. Representative portions of
each sample were then sealed and brought to our laboratory in Marietta, Georgia for further
visual examination and laboratory testing.
Pearl Street - Stormwater
ECS Project No. 10:6178
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Laboratory Testing Program
Representative soil samples were selected and tested in our laboratory to check visual
classifications and to determine pertinent engineering properties. The laboratory testing
program included visual classifications of all soil samples as well as gradation analysis,
Atterberg limits, and natural moisture content testing on selected soil samples.
An experienced geotechnical engineer/geologist classified each soil sample on the basis of
texture and plasticity in accordance with the Unified Soil Classification System. The group
symbols for each soil type are indicated in parentheses following the soil descriptions on the
boring logs. The geotechnical engineer/geologist grouped the various soil types into the major
zones noted on the boring logs. The stratification lines designating the interfaces between earth
materials on the boring logs and profiles are approximate; in-situ, the transitions may be
gradual.
The soil samples will be retained in our laboratory for a period of 60 days, after which, they will
be discarded unless other instructions are received as to their disposition.
SUBSURFACE CONDITIONS
Regional Geology
The site is located in the Piedmont Region of Georgia. According to the Geology of the Greater
Atlanta Region (1984), the site is in the Clarkston Formation with underlying bedrock consisting
of amphibolite and schist. The natural soils at the site consist primarily of residual materials
formed from the in-place physical and chemical weathering of the underlying parent bedrock.
The relative density of the residual soils is primarily dependent upon the degree of weathering,
surface disturbance, groundwater action, and residual mineral bonding. The shear strength of
residual soils is anisotropic and exhibits great variations from point to point. Soils with the flaky
minerals oriented parallel to the potential shear plane and the slickenside surfaces have lower
shear strengths.
The boundary between soil and rock is not clearly defined. A transitional zone called partially
weathered rock (PWR) is normally found above the parent rock. PWR is defined for
engineering purposes, as residual material with standard penetration resistances in excess of
100 blows per foot. Weathering is facilitated by fractures, joints, and the presence of less
resistant rock types. Consequently, PWR and hard rock profiles are irregular and zones of
PWR or rock may occur within the soil mantle well above the general bedrock level. In some
cases, boulders can be found in the upper soil matrix.
Groundwater levels are irregular in the Piedmont Region. The surface of the groundwater table
is largely dependent on the topography and is generally parallel to the ground surface. It can
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ECS Project No. 10:6178
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exhibit some distortions due to differences in vertical and horizontal permeability.
groundwater table can fluctuate several feet with seasonal rainfall.
The
Based on the online Soil Survey of Fulton County, Georgia, as prepared by the US Department
of Agriculture Soil Conservation Service, a summary of the predominant soil types (within the
upper 5 feet below original grade) at the site and their characteristics is included in the following
table:
Soil Type
Constituents
Internal
Drainage
CeC2 - Cecil sandy loam
ReD - Rion sandy loam
Ub - Urban land
UfC2 - Urban land-Cecil
complex
UrE - Urban land-Rion
complex
Sands, Clays
Sands, Clays
No information
Well drained
Well drained
No information
Seasonal High
Water Table
(inches)
80+
80+
No information
Sands, Clays
Well drained
80+
Sands, Clays
Well drained
80+
Soil Conditions
Data from the soil test borings is included in the Appendix. The subsurface conditions
discussed in the following paragraphs and those shown on the boring logs represent an
estimate of the subsurface conditions based on interpretation of the boring data using normally
accepted geotechnical engineering judgments. We note that the transition between different
soil strata is usually less distinct than those shown on the boring logs.
The borings performed for this study typically encountered fill soils underlain by alluvial soils or
residual soils to the explored depth of the borings. One of the borings did not penetrate through
the upper fill. Partially weathered rock and auger refusal material were not encountered to the
boring termination depths.
Fill Materials
Fill may be any material that has been transported and deposited by man.
Undocumented fill is considered any man placed materials with no moisture-density
records at the time it was placed. Materials described as undocumented fill were
encountered in Borings B-1, B-2, B-3, and B-4 to depths of approximately 3 to 35+ feet
below the existing ground surface. The fill material generally consisted of very soft to
very stiff sandy Clay and/or very loose to medium dense silty and clayey Sand.
Standard Penetration resistances (N-Values) ranged from 2 to 24 blows per foot (bpf).
Unsuitable inclusions such as wood / root fragments were visually observed in the soil
Pearl Street - Stormwater
ECS Project No. 10:6178
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samples of Borings B-1 and B-2. Boring B-1 was terminated in the fill materials due to
budgetary constraints.
Alluvial Soils
Alluvium is a material that has been transported and deposited by flowing water. Alluvial
soils consisting of very loose clayey Sand were encountered below the fill materials in
Boring B-3 from 3 to 8 feet below existing grade. The N-Values ranged from 2 to 3 bpf.
Residual Soils
Residual soil, formed by in-place weathering of the parent rock, was encountered in
Borings B-2, B-3, and B-4 below the fill materials and/or alluvial soils. The soil was
generally described as very loose to dense micaceous silty Sand (SM). The N-Values
ranged from 3 to 38 bpf.
Partially Weathered Rock
Partially weathered rock (PWR) is a transitional material between soil and rock, which
retains the relic structure of the rock and exhibits Standard Penetration resistances
greater than 100, but still can be penetrated by the power auger. PWR was not
encountered in the borings performed to termination depths.
Auger Refusal Materials
Refusal is a designation applied to any material which cannot be further penetrated by
the power auger and is normally indicative of a very hard or very dense material, such as
boulders, rock lenses, or the upper surface of bedrock. Auger refusal was not
encountered in the borings performed to termination depths.
Groundwater Conditions
No groundwater seepage in the open bore holes was observed during our fieldwork activities.
Observations for groundwater were made during sampling and upon completion of the drilling
operations at each boring location. In auger drilling operations, water is not introduced into the
boreholes, and the groundwater position can often be determined by observing water flowing
into or out of the boreholes. Furthermore, visual observation of the soil samples retrieved
during the auger drilling exploration can often be used in evaluating the groundwater conditions.
Pearl Street - Stormwater
ECS Project No. 10:6178
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ANALYSIS AND RECOMMENDATIONS
Sewer Lines
During installation of the proposed sewer lines, the proposed bearing surface should be
evaluated in the field by an ECS representative. If unsuitable materials (organically laden fill
materials) are observed at the bearing level, these materials should be over-excavated 2 to 3
feet below proposed invert elevation and replaced with #57 stone or other acceptable fill. The
actual extent of this over-excavation will be determined at the time of construction. Because the
sewer line creates a net unload situation, we do not anticipate any significant settlement of the
newly installed pipe.
Slopes / Trench Box
Our exploration did not include an analysis of slope stability for any temporary or permanent
condition. However, within construction areas, we recommend temporary cut slopes without
seepage be no steeper than 1.5H:1V and permanent cut or fill slopes without seepage be no
steeper than 2H:1V for construction to 20 foot heights in the existing site soils. Slopes
exceeding 20 feet in height or subject to seepage should be evaluated in more detail.
During construction, temporary slopes should be regularly evaluated for signs of movement,
seepage, or an unsafe condition. Soil slopes should be covered for protection from rain, and
surface runoff condition. Stormwater runoff should be diverted away from the slopes. For
erosion protection, a protective cover of grass or other vegetation should be established on
permanent soil slopes as soon as possible.
If near vertical trench walls are planned in excavations deeper than 4 feet, a trench box or other
temporary shoring must be used to meet OSHA safety requirements.
Fill Placement
The preparation of fill subgrades should be observed on a full-time basis by a representative of
ECS to ensure that any unsuitable materials have been removed and that the subgrade is
suitable for support of the proposed construction and/or fills.
Fill materials should consist of an approved material free of organic matter and debris, with
rocks less than 6 inches and a Liquid Limit less than 40 and a Plasticity Index less than 20.
Unacceptable fill materials include topsoil, organic materials, lightweight material with a
maximum dry density less than 95 pcf, and highly plastic silts and clays. All unsuitable
materials removed during grading operations should be either stockpiled for later use in
landscaped areas, or placed in approved disposal areas either on site or off site.
In general, the existing fill materials and alluvial soils appear generally unsuitable for re-use as
structural fill without remedial improvements. Remedial improvements may include screening
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ECS Project No. 10:6178
Page 7
and drying. Depending on the rainfall conditions at the time of construction, the clayey fill
materials and alluvial soils at the site could become unworkable. Existing and offsite fill
materials should be tested by ECS prior to use as structural fill.
The expanded footprint of the proposed alignment should be well defined including the limits of
the fill zones at the time of fill placement. Grade control should be maintained throughout the fill
placement operations. All fill operations should be observed on a full-time basis by a qualified
soil technician from ECS to determine that minimum compaction requirements are being met. A
minimum of one compaction test per 2,500 square foot trench area should be tested in every
one foot compacted lift placed. The elevation and location of the tests should be clearly
identified and recorded at the time of fill placement.
Fill materials should be placed in lifts not exceeding 8 inches in loose thickness and moisture
conditioned to within +/- 3 percent of the optimum moisture content to facilitate proper
compaction. Controlled fill soils should be compacted to a minimum of 95 percent of the
maximum dry density obtained in accordance with ASTM Specification D-698, Standard Proctor
Method.
Additional Considerations
Exposure to the environment may weaken the soils at the pipe bearing level if the excavations
remain open for too long a time. Therefore, pipes should be placed the same day that
excavations are dug. If surface water intrusion or exposure softens the bearing soils, the
softened soils must be removed from the excavation bottom immediately prior to placement of
the pipes. If the excavation must remain open overnight, or if rainfall becomes imminent while
the bearing soils are exposed, we recommend that the excavations be covered or otherwise
protected.
Positive site drainage should be maintained during earthwork operations, which should help
maintain the integrity of the soil. Placement of fill on the near surface soils, which have become
saturated, could be very difficult. When wet, these soils will degrade quickly with disturbance
from contractor operations and will be extremely difficult to stabilize for fill placement.
Where unacceptable materials are encountered, they must be undercut and replaced or
improved by recompaction. On a previously filled site, the contractor must be especially alert for
the possible existence of poor soil conditions that may become apparent during construction.
The surface of the site should be kept properly graded in order to enhance drainage of the
surface water away from the proposed structure areas during the construction phase. We
recommend that an attempt be made to enhance the natural drainage without interrupting its
pattern.
The surficial soils contain fines, which are considered moderately erodible. All erosion and
sedimentation shall be controlled in accordance with Best Management Practices and current
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ECS Project No. 10:6178
Page 8
County and State NPDES requirements. At the appropriate time, we would be pleased to
provide a proposal for conducting construction materials testing and NPDES services.
CLOSING
This report has been prepared in accordance with generally accepted geotechnical engineering
practice. No warranty is expressed or implied. The evaluations and recommendations
presented in this report are based on the available project information, as well as on the results
of the exploration. ECS should be given the opportunity to review the final drawings and site
plans for this project to determine if changes to the recommendations outlined in this report are
needed.
Because undocumented fill is present on this site, the owner must assess the relative risk that
unacceptable material could have been buried in the proposed pipe alignment which was not
detected in the widely spaced borings. It is critical that ECS be retained to perform compaction
testing and other construction testing on this site. If ECS is not retained for this extension of the
field exploration, we can not be responsible for the performance of the installed pipes.
This report is provided for the exclusive use of Camp Dresser & McKee, Inc., City of East Point,
and their project specific design team. This report is not intended to be used or relied upon in
connection with other projects or by other third parties. ECS disclaims liability for any such third
party use or reliance without express written permission.
Attachments
Appendix I
Approximate
Site Location
N
Figure
No.:
SITE VICINITY MAP
REPORT OF GEOTECHNICAL EXPLORATION
Project No.:
10:6178
Pearl Street - Stormwater
East Point, Georgia
Scale: 1”= 2000’
Reference: USGS Quadrangle: Southwest Atlanta,
Georgia dated 1993
Date: 10/2011
1
80
40
0
20
40
Graphic Scale 1"=80'
60
80
10/11
10/11
Appendix II
UNIFIED SOIL CLASSIFICATION SYSTEM (ASTM D 2487)
a
Laboratory Classification Criteria
GW
Poorly
graded
gravels,
gravel-sand mixtures, little or
no fines
GP
d
GM
Silty gravels,
mixtures
a
gravel-sand
u
GC
Clayey gravels, gravel-sandclay mixtures
SW
Well-graded sands, gravelly
sands, little or no fines
SP
Poorly graded sands, gravelly
sands, little or no fines
d
SM
Silty sands, sand-silt mixtures
a
u
SC
ML
CL
OL
MH
Clayey sands, sand-clay
mixtures
Determine percentages of sand and gravel from grain-size curve.
Depending on percentage of fines (fraction smaller than No. 200 sieve size), coarse-grained soils
are classified as follows:
Less than 5 percent
GW, GP, SW, SP
More than 12 percent GM, GC, SM, SC
b
5 to 12 percent
Borderline cases requiring dual symbols
Sands with fines
(Appreciable amount of
fines)
(Liquid limit less than 50)
Silts and clays
Silts and clays
(Liquid limit greater than 50)
Typical Names
Well-graded gravels, gravelsand mixtures, little or no
fines
Inorganic silts and very fine
sands, rock flour, silty or
clayey fine sands, or clayey
silts with slight plasticity
Inorganic clays of low to
medium plasticity, gravelly
clays, sandy clays, silty clays,
lean clays
Organic silts and organic silty
clays of low plasticity
Inorganic silts, micaceous or
diatomaceous fine sandy or
silty soils, elastic silts
CH
Inorganic clays
plasticity, fat clays
of
high
OH
Organic clays of medium to
high plasticity, organic silts
Cu = D60/D10 greater than 4
2
Cc = (D30) /(D10xD60) between 1 and 3
Not meeting all gradation requirements for GW
Atterberg limits below “A” line
or P.I. less than 4
Above “A” line with P.I.
between 4 and 7 are
borderline cases requiring
use of dual symbols
Atterberg limits below “A” line
or P.I. less than 7
Cu = D60/D10 greater than 6
2
Cc = (D30) /(D10xD60) between 1 and 3
Not meeting all gradation requirements for SW
Atterberg limits above “A” line
or P.I. less than 4
Limits plotting in CL-ML
zone with P.I. between 4
and 7 are borderline
cases requiring use of
dual symbols
Atterberg limits above “A” line
with P.I. greater than 7
Plasticity Chart
60
"A" line
50
CH
Plasticity Index
Clean gravels
(Little or no
fines)
Clean sands
(Little or no
fines)
Gravels with fines
(Appreciable amount of
fines)
Gravels
(More than half of coarse fraction is
larger than No. 4 sieve size)
Sands
(More than half of coarse fraction is
smaller than No. 4 sieve size)
Group
Symbols
40
CL
30
20
MH and OH
10
CL-ML
0
0
Highly
Organic
soils
Fine-grained soils
(More than half material is smaller than No. 200 Sieve)
Coarse-grained soils
(More than half of material is larger than No. 200 Sieve size)
Major Divisions
Pt
Peat and other highly organic
soils
10
20
ML and OL
30
40
50
60
70
80
90
100
Liquid Limit
Division of GM and SM groups into subdivisions of d and u are for roads and airfields only. Subdivision is based on Atterberg limits; suffix d used when
L.L. is 28 or less and the P.I. is 6 or less; the suffix u used when L.L. is greater than 28.
b
Borderline classifications, used for soils possessing characteristics of two groups, are designated by combinations of group symbols. For example:
GW-GC,well-graded gravel-sand mixture with clay binder.
(From Table 2.16 - Winterkorn and Fang, 1975)
REFERENCE NOTES FOR BORING LOGS
I.
Drilling Sampling Symbols
SS
RC
DC
BS
HSA
REC
II.
Split Spoon Sampler
Rock Core, NX, BX, AX
Dutch Cone Penetrometer
Bulk Sample of Cuttings
Hollow Stem Auger
Rock Sample Recovery %
Shelby Tube Sampler
Pressuremeter
Rock Bit Drilling
Power Auger (no sample)
Wash sample
Rock Quality Designation %
Correlation of Penetration Resistances to Soil Properties
Standard Penetration (blows/ft) refers to the blows per foot of a 140 lb. hammer falling 30
inches on a 2-inch OD split-spoon sampler, as specified in ASTM D 1586. The blow count is
commonly referred to as the N-value.
A.
Non-Cohesive Soils (Silt, Sand, Gravel and Combinations)
Density
Under 4 blows/ft
Very Loose
5 to 10 blows/ft
Loose
11 to 30 blows/ft
Medium Dense
31 to 50 blows/ft
Dense
Over 51 blows/ft
Very Dense
Boulders
Cobbles
Gravel
Sand
Coarse
Medium
Fine
Coarse
Medium
Fine
Silt and Clay
B.
III.
ST
PM
RD
PA
WS
RQD
Relative Properties
Adjective Form
12% to 49%
With
5% to 12%
Particle Size Identification
8 inches or larger
3 to 8 inches
1 to 3 inches
½ to 1 inch
¼ to ½ inch
2.00 mm to ¼ inch (dia. of lead pencil)
0.42 to 2.00 mm (dia. of broom straw)
0.074 to 0.42 mm (dia. of human hair)
0.0 to 0.074 mm (particles cannot be seen)
Cohesive Soils (Clay, Silt, and Combinations)
Blows/ft
Consistency
Under 2
3 to 4
5 to 8
9 to 15
16 to 30
31 to 50
Over 51
Very Soft
Soft
Medium Stiff
Stiff
Very Stiff
Hard
Very Hard
Unconfined
Comp. Strength
Qp (tsf)
Under 0.25
0.25-0.49
0.50-0.99
1.00-1.99
2.00-3.00
4.00–8.00
Over 8.00
Degree of
Plasticity
Plasticity
Index
None to slight
Slight
Medium
High to Very High
0–4
5–7
8 – 22
Over 22
Water Level Measurement Symbols
WL Water Level
WS While Sampling
WD While Drilling
BCR Before Casing Removal
ACR After Casing Removal
Est. Groundwater Level
DCI
Dry Cave-In
WCI
Wet Cave-In
Est. Seasonal High GWT
The water levels are those levels actually measured in the borehole at the times indicated by the
symbol. The measurements are relatively reliable when augering, without adding fluids, in a granular
soil. In clay and plastic silts, the accurate determination of water levels may require several days for
the water level to stabilize. In such cases, additional methods of measurement are generally applied.
Appendix III