HomeMy WebLinkAboutSUB201900058 Other 2021-02-08Report of Geotechnical Study
Pleasant Green Connector Road Culvert
Albemarle County, Virginia
F&R Project No. 71Z0001
Prepared For:
Stanley Martin Homes
404 People Place, Suite 303
Charlottesville, Virginia 22911
Prepared By:
Froehling & Robertson, Inc.
6185 Rockfish Gap Turnpike
Crozet, Virginia 23932-3330
January 22, 2021
Corporate HQ: 3015 Dumbarton Road Richmond, Virginia 23228 T804.264.2701 F 804.264.1202 www.fandr.com
VIRGINIA • NORTH CAROLINA • SOUTH CAROLINA • MARYLAND • DISTRICT OF COLUMBIA
A Minority -Owned Business
FROEHLING & ROBERTSON, INC.
�Q Engineering Stability Since 1881
�C 6185 Rockfish Gap Turnpike
® Crozet, Virginia 22932-3330
T 434.823.5154 1 F 434.823.4764
January 22, 2021
Mr. Gregg O'Donnell
Stanley Martin Homes
404 People Place, Suite 303
Charlottesville, Virginia 22911
Reference: Report of Geotechnical Study
Pleasant Green Connector Road Culvert
Albemarle County, Virginia
F&R Project No. 71Z0001
Dear Mr. O'Donnell:
The purpose of this study is to present the results of the subsurface exploration program and geotechnical
engineering evaluation undertaken by F�oehling & Robertson, Inc. (F&R) in connection with the referenced
project. Our services were performed in general accordance with F&R Proposal No. 2071-0332G dated
December 17, 2020. The attached report presents our understanding of the project, reviews our
exploration procedures, describes existing site and general subsurface conditions, and presents our
geotechnical evaluations and recommendations.
We have enjoyed working with you on this project, and we are prepared to assist you with the
recommended quality assurance monitoring and testing services during construction. Please contact us if
you have any questions regarding this report or if we may be of further service.
Sincerely,
FROEHLING & ROBERTSON, INC.
CAS/Neel
Matthew E. DuBois, P.E.
Senior Engineer
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CLYDE A. SIMMONS, III 5
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Clyde A. Simmons, III, P.E.
Senior Geotechnical Engineer
J:\Projects 71Z\71Z0001( Pleasant Green Connector Road Culvert)\Report\Pleasant Green Connector Road Culvert Report.doa
Corporate HQ: 3015 Dumbarton Road Richmond, Virginia 23228 T 804.264.2701 F 804.264.1202 www.fandr.com
VIRGINIA • NORTH CAROLINA • SOUTH CAROLINA • MARYLAND • DISTRICT OF COLUMBIA
A Minority -Owned Business
F&R
TABLE OF CONTENTS
SECTION
PAGE
1.0 PURPOSE & SCOPE OF SERVICES.................................................................................. 1
2.0 PROJECT INFORMATION..............................................................................................2
2.1 SITE DESCRIPTION......................................................................................................... 2
2.2 PROPOSED CONSTRUCTION............................................................................................. 2
3.0 EXPLORATION PROCEDURES........................................................................................2
3.1 SUBSURFACE EXPLORATION............................................................................................. 2
3.2 LABORATORY TESTING................................................................................................... 4
4.0 REGIONAL GEOLOGY & SUBSURFACE CONDITIONS......................................................4
4.1 REGIONAL GEOLOGY...................................................................................................... 4
4.2 SUBSURFACE CONDITIONS............................................................................................... 5
4.2.1 General.............................................................................................................5
4.2.2 Surficial Materials.............................................................................................5
4.2.3 Alluvial Soils......................................................................................................6
4.2.4 Residual Soils....................................................................................................6
4.2.5 Soft Weathered Rock........................................................................................ 6
4.2.6 Auger Refusal Materials....................................................................................6
4.3 SUBSURFACE WATER..................................................................................................... 7
4.4 LABORATORY TEST RESULTS............................................................................................ 7
5.0 GEOTECHNICAL DESIGN RECOMMENDATIONS.............................................................8
5.1 GENERAL.................................................................................................................... 8
5.2 BOX CULVERTS............................................................................................................. 8
5.3 SETTLEMENT................................................................................................................ 9
5.4 LATERAL EARTH PRESSURES............................................................................................. 9
6.0 GEOTECHNICAL CONSTRUCTION RECOMMENDATIONS .............................................. 11
6.1 SITE PREPARATION...................................................................................................... 11
6.2 EXCAVATION CONDITIONS............................................................................................. 11
6.3 FOUNDATION CONSTRUCTION........................................................................................ 12
6.4 STRUCTURAL FILL PLACEMENT AND COMPACTION............................................................... 12
6.5 SURFACE WATER/GROUNDWATER CONTROL..................................................................... 13
6.6 TEMPORARY EXCAVATION RECOMMENDATIONS................................................................. 14
7.0 CONTINUATION OF SERVICES.................................................................................... 15
8.0 LIMITATIONS.............................................................................................................16
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F&R
APPENDICES
APPENDIX I
Site Vicinity Map (Drawing No. 1)
Boring Location Plan (Drawing No. 2)
APPENDIX II
Key to Boring Log Soil Classification
Classification of Soils for Engineering Purposes
Soil Classification Chart
Boring Logs
Subsurface Profile
APPENDIX III
GBA Document "Important Information about Your Geotechnical Engineering Report'
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1.0 PURPOSE & SCOPE OF SERVICES
The purpose of the subsurface exploration and geotechnical engineering evaluation was to
explore the subsurface conditions in the area of the proposed development and provide
geotechnical engineering design and construction recommendations that can be used during the
design and construction of the proposed structures.
F&R's scope of services included the following:
• Visited the site to observe existing surface conditions;
• Coordinated utility clearance with Miss Utility;
• Reviewed readily available geologic and subsurface information relative to the project site;
• Completion of two soil test borings to depths of 22.2 feet and 5.4 feet below the existing
ground surface;
• Preparation of typed Boring Logs and development of a Subsurface Profile;
• Performing geotechnical laboratory testing on representative soil samples;
• Performing a geotechnical engineering evaluation of the subsurface conditions with regard
to their suitability for the proposed construction;
• Provided recommendations regarding lateral earth pressure coefficients for the design of
below grade walls by others.
• Provided recommendations regarding the placement and compaction of fill materials
required to achieve site subgrades, including an assessment of the suitability of the on -site
soil for re -use as structural fill, and recommendations regarding rock excavation;
• Preparation of this geotechnical report by professional engineers.
Our scope of services did not include a survey of the boring locations, rock coring, quantity
estimates, preparation of plans or specifications, or the identification and evaluation of wetland
or other environmental aspects of the project site.
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2.0 PROJECT INFORMATION
2.1 Site Description
The project site is located on the southwest side of the Pleasant Green Subdivision in Albemarle
County, Virginia (See Site Location Plan, Drawing No. 1, Appendix 1). The culverts are planned for
a new road that will connect the roundabout on Alston Street in the Pleasant Green Subdivision
with Orchard Drive to the west. The project corridor is mostly wooded, but clearing has been
performed for a sanitary sewer line located to the south of the road. The new road will cross
Powells Creek near the midpoint between the two existing roads. The existing grades range from
approximately El 708 at Alston Street down to El 687 at Powells Creek and back up to El 710 at
Orchard Drive.
2.2 Proposed Construction
Project information was provided by email and included the "Connector Road Plans and Profile,"
Sheet 3, by Collins Engineering, dated 11/16/2020, and the calculations and drawings for the box
culverts by Winchester Precast dated 12/3/2020. We understand that the project will consist of
three precast concrete box culverts, each 8 feet tall and 10 feet wide at the crossing of Powells
Creek near Station 13+00 of the Connector Road. The culverts are planned to be approximately
90 feet long with concrete endwalls at each end. The invert levels for the culverts are planned
between El 686.75 and El 688.0. Finished grade for the roadway is planned to be approximately
6 feet above the top of the culverts.
3.0 EXPLORATION PROCEDURES
3.1 Subsurface Exploration
The exploration program was performed on January 7, 2021, and consisted of two soil test
borings designated B-01 and B-02. An F&R geologist was onsite to monitor drilling, logging the
borings, and performing visual classification of the recovered samples during the exploration
program. Boring B-01 was extended past the planned termination depth of 20 feet due to very
loose materials encountered at the planned termination depth. Boring B-01 encountered auger
refusal at 22 feet below existing grades. Boring B-02 encountered auger refusal at a depth of 5.4
feet below existing grades. An offset boring, drilled 8 feet west of boring B-02 to confirm the
auger refusal depth also encountered auger refusal at a depth of 5.4 feet below existing grades.
The locations of the borings are shown on the attached Boring Location Plan (Drawing No. 2,
Appendix 1). The test boring locations were staked in the field by F&R by measuring off of existing
site features. The elevations shown on the boring logs were interpolated from the provided
plans. Given that some minor shifting of pre -staked locations may have occurred during drilling,
we recommend that the test boring locations and elevations shown on the attached Boring
Location Plans and Boring Logs be considered approximate.
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The soil test borings were performed in accordance with generally accepted practice using a
track -mounted Diedrich D-50 rotary drill rig equipped with an automatic hammer. Hollow -stem
augers were advanced to pre -selected depths, the center plug was removed, and representative
soil samples were recovered with a standard split -spoon sampler (13/8 in. ID, 2 in. OD) in general
accordance with ASTM D 1586, the Standard Penetration Test. For these tests, a weight of 140
pounds was freely dropped from a height of 30 inches to drive the split -spoon sampler into the
soil. The number of blows required to drive the split -spoon sampler three consecutive 6-inch
increments was recorded, and the blows of the last two increments were summed to obtain the
Standard Penetration Resistance (N-value). The N-value provides a general indication of in -situ
soil conditions and has been correlated with certain engineering properties of soils.
Research has shown that the Standard Penetration Resistance (N-value) determined by
automatic hammer is different than the N-value determined by the safety hammer method.
Most corrections that are published in technical literature are based on the N-value determined
by the safety hammer method. This is commonly termed N6o as the rope and cathead with a
safety hammer delivers about 60 percent of the theoretical energy delivered by a 140-pound
hammer falling 30 inches. Several researchers have proposed correction factors for the use of
hammers other than the safety hammer. The correction is made by the following equation:
N60 = Nfield X CE
where Nfield is the value recorded in the field, and CE is the drill rod energy ratio for the hammer
used. The guidelines provided in the Performance and Use of the Standard Penetration Test in
Geotechnical Engineering Practice manual published by the Center for Geotechnical Practice and
Research at the Virginia Polytechnic Institute and State University recommend that a correction
factor (CE) be used to convert Nfield values to N6o values when using an automatic hammer. We
recommend that a correction factor (CE) of 1.3 be used to convert Nfield to N60 values.
Plotted N-values reported on Boring Logs are the actual, field -derived blow counts (Nfield). Drilling
notes on each Boring Log indicates whether penetration resistances presented on the Boring Log
were determined using automatic hammer or conventional hammer systems. Corrected N60
values were used for all analyses.
The test borings were advanced through the soil overburden by soil drilling procedures to the
planned termination depth or until auger refusal materials were encountered. Subsurface water
level readings were taken in each of the borings immediately upon completion of the drilling
process. Upon completion of drilling, the boreholes were backfilled with auger cuttings (soil).
Periodic observation of the boreholes should be performed to monitor subsidence at the ground
surface, as the borehole backfill could settle over time.
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Representative portions of the split -spoon soil samples obtained throughout the exploration
program were placed in glass jars and transported to our laboratory. In the laboratory, the soil
samples were evaluated by a member of our engineering staff in general accordance with
techniques outlined in the visual -manual identification procedure (ASTM D 2488). The soil
descriptions and classifications discussed in this report and shown on the attached Boring Logs
are based on visual observation and should be considered approximate. A copy of the boring
logs are provided and classification procedures are further explained in Appendix II.
Split -spoon soil samples recovered on this project will be stored at F&R's office for a period of 60
days. After 60 days, the samples will be discarded unless prior notification is provided to us in
writing.
3.2 Laboratory Testing
Representative soil samples were subjected to Water Content (ASTM D 2216), Atterberg Limits
(ASTM C4318) and #200 Sieve Wash (ASTM D1140) testing to substantiate the visual
classifications and assist with the estimation of the soils' pertinent engineering properties. PH
and resistivity testing were also performed to estimate the soil's corrosive potential. Test results
are provided in Section 4.4 of this report
4.0 REGIONAL GEOLOGY & SUBSURFACE CONDITIONS
4.1 Regional Geology
The project site is located in the upland area of the Piedmont Plateau, at the western edge of the
Piedmont Physiographic Province, an area underlain by ancient metamorphic rocks. Information
obtained from the Geologic map of Virginia (1993) indicates that the project site is underlain by
Charnockite, a Plutonic Rock of Grenville Age. The virgin soils encountered in this area are the
residual product of in -place chemical and mechanical weathering of the parent bedrock
formation that underlies the site. These materials consist of SILT and CLAY soils near the surface
where soil weathering is more advanced, underlain by silty SAND and clayey SAND.
The boundary between soil and rock is often times not sharply defined. The transitional term
"Hard or Soft Weathered Rock" is normally found overlying the parent bedrock. For engineering
purposes, SWR is described as broken and partially weathered rock with Standard Penetration
Resistance N-values between 50 blows per 6 inches and 50 blows per inch. HWR is described as
broken and partially weathered rock with N values in excess of 50 blows per inch.
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Weathering is facilitated by fractures, joints and the presence of less resistant rock types.
Consequently, the profile of the SWR or HWR is often quite irregular, even over very short
horizontal distances. Also, it is not unusual to find lenses, layers, or zones of less resistant SWR
and more resistant HWR, and boulders of hard rock within the soil mantle well above the general
bedrock level.
4.2 Subsurface Conditions
4.2.1 General
The subsurface conditions discussed in the following paragraphs and those shown on the
attached Boring Logs and Subsurface Profile represent an estimate of the subsurface conditions
based on interpretation of the boring data using normally accepted geotechnical engineering
judgments. The transitions between different soil strata are usually less distinct than those
shown on the boring logs. Sometimes the relatively small sample obtained in the field is
insufficient to definitively describe the origin of the subsurface material. In these cases, we
qualify our origin descriptions with "possible" before the word describing the material's origin
(i.e. possible fill, etc.). Although individual soil test borings are representative of the subsurface
conditions at the boring locations on the dates shown, they are not necessarily indicative of
subsurface conditions at other locations or at other times. Data from the specific soil test borings
is shown on the attached Boring Logs in Appendix II. The subsurface profile, which is a composite
of the boring data, is included in Appendix II.
Below the existing ground surface, the borings generally encountered surficial materials, alluvial
soils, residual soils, soft weathered rock, and auger refusal materials. These materials are
generally discussed in the following paragraphs.
4.2.2 Surficial Materials
Surficial organic soils were encountered in each of the borings to depths of approximately 4
inches. Surficial organic soil is typically a dark -colored soil material containing roots, fibrous
matter, and/or other organic components, and is generally unsuitable for engineering purposes.
F&R has not performed any laboratory testing to determine the organic content or other
horticultural properties of the observed surficial organic soil materials. Therefore, the term
surficial organic soil is not intended to indicate a suitability for landscaping and/or other
purposes. The surficial organic soil depths provided in this report are based on driller
observations and should be considered approximate. We note that the transition from surficial
organic soil to underlying materials may be gradual, and therefore the observation and
measurement of surficial organic soil depths is subjective. Thicker layers of surficial organics
should be expected in wooded areas to account for the presence of root balls. Actual surficial
organic soil depths should be expected to vary.
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4.2.3 Alluvial Soils
Alluvial soils, placed by moving water, were encountered in each boring, below the surficial
organics and extended a depth of 6 feet in boring B-01 and to the refusal depth of 5.4 feet in
boring B-02. Sampled alluvium consisted of Lean CLAY (CL), SILT (MIL), silty SAND (SM), and silty
GRAVEL (GM) with varying amounts of sand and gravel. Sampled alluvium was brown, tan brown,
and gray in color, with water contents visually characterized as very moist to wet. The Standard
Penetration Test values (N-values) in the alluvium ranged from 3 bpf to 100+ bpf. The higher N-
values obtained in the alluvium layer are attributable to gravel and cobbles deposited within the
alluvial soils.
4.2.4 Residual Soils
Residual Soils, formed by the in -place weathering of the parent rock, were encountered below
the alluvial soils in boring B-01 and extended to the soft weathered rock layer. The residual soils
were generally described as sandy SILT (MIL), or silty SAND (SM). The sampled residual soils were
brown and tan, in color, with moisture contents visually characterized as wet. N-values in the
residual soils ranged from 2 bpf to 18 bpf.
4.2.5 Soft Weathered Rock
Soft weathered rock (SWR) is a transitional material between soil and rock which contains the
relic structure of the rock with very hard consistencies or very dense densities. SWR materials
were encountered boring B-01 below the residual soils at a depth of 22 feet to the auger refusal
depth of 22.2 feet below existing grades. When sampled, the SWR became gray, wet, silty SAND
(SM). The N-value in the SWR was 50/2.
4.2.6 Auger Refusal Materials
Auger refusal occurs when materials are encountered that cannot be penetrated bythe soil auger
and is normally indicative of a very hard or very dense material, such as boulders, rock lenses,
rock pinnacles, or the upper surface of rock. Auger refusal was encountered in boring B-01 at a
depth of 22.2 feet and in B-02 at a depth of 5.4 feet below existing grades. An offset boring was
performed 8 feet west of B-02 and also encountered refusal at a depth of 5.4 feet below existing
grades. Auger refusal conditions with a Diedrich D-50 drill rig do not necessarily indicate
conditions impenetrable to other equipment. Auger refusal conditions will likely vary in
unexplored areas of the site.
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4.3 Subsurface Water
The test borings were monitored during and after drilling operations to obtain short-term
subsurface water information. Subsurface water was encountered at depths of 2.5 to 5 feet
below existing grades. It is anticipated that the groundwater elevation should closely match that
of the water level in Powells Creek. It should be noted that the location of the subsurface water
table could vary by several feet because of seasonal fluctuations in precipitation, evaporation,
surface water runoff, local topography, and other factors not immediately apparent at the time
of this exploration. Normally, the highest subsurface water levels occur in the late winter and
spring and lowest levels occur in the late summer and fall.
4.4 Laboratory Test Results
As discussed in Section 3.2, laboratory testing was performed on selected soil samples collected
during our subsurface exploration. The results from the laboratory testing are included in the
following table.
Boring
No.
Sample Depth
(Feet)
Natural Water
Content (%)
Liquid Limit/
Plasticity Index
% Passing
No. 200 Sieve
USCS
Class.
B-01
0-2
17.1
B-01
2-4
23.2
27/7
36.1
SM
B-01
4-6
21.1
B-01
6-8
40.6
B-01
8-10
26.4
B-01
13.5-15
21.1
B-01
18.5-20
30.0
B-02
0-2
19.3
B-02
2-4
21.7
42/18
52.1
CL
B-02
4-6
13.8
PH and resistivity testing was performed on a composite sample collected at a depth of 4 to 6
feet below existing grades at boring B-01 to evaluate the potential corrosivity of the on -site
materials. The pH of the sample was 5.2 and the resistivity was 8,620 ohm -cm.
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5.0 GEOTECHNICAL DESIGN RECOMMENDATIONS
5.1 General
The following evaluations and recommendations are based on our observations at the site,
interpretation of the field data obtained during this exploration, and our experience with similar
subsurface conditions and projects. Soil penetration data has been used to estimate an allowable
bearing pressure and associated settlement using established correlations. Subsurface
conditions in unexplored locations may vary from those encountered. If the structure locations,
loadings, or elevations are changed, we should be notified and requested to confirm and, if
necessary, re-evaluate our recommendations.
Determination of an appropriate foundation system for a given structure is dependent on the
proposed structural loads, soil conditions, and construction constraints such as proximityto other
structures, etc. The subsurface exploration aids the geotechnical engineer in determining the
soil stratum appropriate for structural support. This determination includes considerations with
regard to both allowable bearing capacity and compressibility of the soil strata. In addition, since
the method of construction greatly affects the soils intended for structural support, consideration
must be given to the implementation of suitable methods of site preparation, fill compaction,
and other aspects of construction, where applicable.
5.2 Box Culverts
We understand that the proposed crossing is planned to consist of three precast concrete box
culverts, each 8 feet tall and 10 feet wide. The culvert will be approximately 90 feet long with
concrete endwalls at each end. Based on the results of the subsurface exploration, it is
anticipated that the box culvert will be supported by alluvial soils or rock. We recommend that
shallow foundations be designed for a net allowable bearing pressure not to exceed 2,000
pounds per square foot (psf).
Typical bedding materials, as required by VDOT or Albemarle County, should be adequate,
provided that firm subgrade soils are present. We recommend that the box culvert subgrades
be observed by the geotechnical engineer to determine if suitable subgrade conditions are
present. Where soft or very loose consistency soils, such as those encountered in B-01 from a
depth of 6 to 8 feet below grade are encountered, they should be undercut and replaced with
VDOT No. 57 stone down to suitable firm materials. Where VDOT No. 57 stone or similar open
graded materials are used as backfill, they should be encased with a geotextile filter fabric. If the
soft soils extend to a significant depth such that complete removal is not practical, F&R should
be consulted to provide a recommendation. In general, this issue can be addressed by using
geosynthetics and possibly widening the base of the excavation. If rock is encountered within
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the excavation for the box culverts, it should be removed to a depth of 8 inches below the bottom
of the precast culvert and replaced with VDOT No. 57 stone or other bedding material as required
by VDOT. This "cushion" of material between the rock and the bottom of the culvert will reduce
any point loading on the box culvert.
F&R recommends that the walls be backfilled with No. 57 stone. A friction angle of 40 degrees
and a moist unit weight of 115 pcf can be used for earth pressure calculations with the No. 57
Stone. Considering the anticipated subgrade soils, F&R recommends a base friction coefficient
of 0.34 and a sliding resistance factor (0z) of 0.5 be used for sliding calculations.
The following comments are based on the results of the pH and resistivity testing and available
references regarding soil corrosion potential. A soil sample from the on -site borrow area was
tested for pH and resistivity, with results of 5.3 and 8,620 ohm -cm. The soils tested generally
exhibit characteristics associated with low corrosion potential. We note that the project
structural and civil designers and/or other applicable parties should also review the soil pH and
resistivity test results for their determination of whether any corrective or preventative actions
are required to protect foundations and other below -grade materials (such as pipes or other
buried steel) from corrosion.
5.3 Settlement
Based on the boring data, proposed grading, and assumed structural information, we estimate
that foundation settlements will be less than 1 inch with differential settlement of up to one-half
the estimated total settlement. The magnitude of differential settlements will be influenced by
the variation in excavation requirements across the foundation footprint, the distribution of
loads, and the variability of underlying soils.
Our settlement analysis was performed on the basis of the assumed structural loading and
provided grading information discussed above. Actual settlements experienced by the structure
and the time required for these soils to settle will be influenced by undetected variations in
subsurface conditions, final grading plans, and the quality of fill placement and foundation
construction.
5.4 Lateral Earth Pressures
Earth pressures on walls below grade are influenced by structural design of the walls, conditions
of wall restraint, methods of construction and/or compaction, and the strength of the materials
being restrained. The most common conditions assumed for earth retaining wall design are the
active and at -rest conditions. Active conditions apply to relatively flexible earth retention
structures, such as freestanding walls, where some movement and rotation may occur to
mobilize soil shear strength. Walls that are rigidly restrained, such as basement, pit, pool and
tunnel walls, should be designed for the structure requiring the use of at -rest earth pressures.
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A third condition, the passive state, represents the maximum possible pressure when a structure
is pushed against the soil, and is used in wall foundation design to help resist active or at -rest
pressures. Because significant wall movements are required to develop the passive pressure, the
total calculated passive pressure should be reduced by one-half to two-thirds for design
purposes.
F&R recommends that VDOT No. 57 Stone be used as below grade wall backfill. The
recommended lateral earth pressure coefficients and equivalent fluid pressure parameters for
design of below grade walls using these materials are provided in the following table.
Lateral Earth
Equivalent Fluid
Soil Type
Base Friction
Coefficient
Pressure
Coefficient (k)
Unit Weight (yeq, pcf)
At -rest
Active
At -rest
Active
Passive
VDOT No. 57 Stone
0.34
0.36
0.22
41
25
300
A moist unit weight of 115 pcf for No. 57 Stone should be used for design calculations. The backfill
material should be extended a minimum distance of 0.5 times the wall height laterally from the
back face of the wall, or for a cantilevered wall, from the heel of the wall footing.
Our recommendations were given assuming that the ground surface above the wall is level. The
recommended equivalent fluid pressures were provided assuming that constantly functioning
drainage systems, consisting of crushed stone blanket drain and slotted 4 inch diameter PVC pipe,
are installed between walls and backfill to preventthe accidental buildup of hydrostatic pressures
and lateral stresses in excess of those stated. If a functioning drainage system is not installed,
then lateral earth pressures should be determined using the buoyant weight of the soil.
Hydrostatic pressures calculated with the unit weight of water (62.4 pcf) should be added to
these earth pressures to obtain the total stresses for design.
Heavy equipment should not operate within 5 feet of below grade walls to prevent lateral
pressures in excess of those cited. Adjacent footings or other surcharge loads located a short
distance outside below grade walls will also exert appreciable additional lateral pressures.
Surcharge loads should be evaluated using the appropriate active or at -rest pressure coefficients
provided above. The effect of surcharge loads should be added to the recommended earth
pressures to determine total lateral stresses.
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F&R
6.0 GEOTECHNICAL CONSTRUCTION RECOMMENDATIONS
6.1 Site Preparation
Before proceeding with construction, existing footings, utilities, concrete and crushed stone, and
other deleterious non -soil materials (if any) should be stripped or removed from the proposed
construction area. Attention should be given to these areas to ensure all unsuitable material is
removed prior to continuing with construction. During the site preparation operations, positive
surface drainage should be maintained to prevent the accumulation of water. Existing
underground utilities should be re-routed to locations a minimum of 10 feet outside of any
proposed structure footings or abandoned in place with flowable fill. Prior to fill placement, the
subgrades to receive backfill should be evaluated by the geotechnical engineer.
6.2 Excavation Conditions
Auger refusal conditions were encountered at approximately 1 foot below the invert location at
boring B-02. F&R notes that the profile of the bedrock surface will be highly irregular, and that
bedrock could be encountered at higher elevations between test boring locations. Therefore,
difficult excavation conditions could be encountered in deeper excavations on site.
In mass excavations for general site work, hard or dense soils (soils with standard penetration
resistances of 30 or more blows per foot) can usually be removed by ripping with a single -tooth
ripper attached to a large crawler tractor or by breaking it out with a tracked excavator or large
front-end loader. However, we note that while ripping and/or breaking out with large tracked
equipment might be possible, it may be time prohibitive for deep mass excavations. Blasting is
not expected due to the limited amount of excavation anticipated to be necessary. In confined
excavations such as foundations, utility trenches, etc., removal of partially weathered rock
typically requires use of large backhoes, pneumatic spades, or expansive grout.
The gradation of the material removed by ripping or blasting is typically erratic, making it
unsuitable for use as structural fill. The definition of rock can be a source of conflict during
construction. The following definitions have been incorporated into specifications on other
projects and are provided for your general guidance:
GENERAL EXCAVATION:
Rip Rock - Any material that cannot be removed by scrapers, loaders, pans,
dozers, or graders; and requires the use of a single -tooth ripper
mounted on a crawlertractor having a minimum draw bar pull rated at
not less than 56,000 pounds.
Stanley Martin Homes
F&R File No. 71Z0001
Page - 11 -
Pleasant Green Connector Road Culvert
January22, 2021
Blast Rock - Any material which cannot be excavated with a single -tooth ripper
mounted on a crawler tractor having a minimum draw bar pull rated at
not less than 56,000 pounds (Caterpillar D-81K or equivalent) or by a
Caterpillar 977 front-end loader or equivalent; and occupying an
original volume of at least one (1) cubic yard.
TRENCH EXCAVATION:
Blast Rock- Any material which cannot be excavated with a backhoe having a bucket
curling force rated at not less than 25,700 pounds (Caterpillar Model 225 or
equivalent), and occupying an original volume of at least one-half (1/2) cubic
yard.
6.3 Foundation Construction
All foundation subgrades should be observed, evaluated, and verified for the design bearing
pressure by the geotechnical engineer after excavation and prior to reinforcement steel
placement. If low consistency soils, such as those encountered in B-01 from 6 to 8 feet below
existing grades are encountered during foundation construction, localized undercutting and/or
in -place stabilization of foundation subgrades will be required. The actual need for, and extent
of, undercutting should be based on field observations made by the geotechnical engineer at the
time of construction.
Excavations for footings should be made in such a way as to provide bearing surfaces that are
firm and free of loose, soft, wet, or otherwise disturbed soils. Foundation concrete should not
be placed on frozen or saturated subgrades. If such materials are allowed to remain below
foundations, settlements will increase. Foundation excavations should be concreted as soon as
practical after they are excavated. If an excavation is left open for an extended period, a thin
mat of lean concrete should be placed over the bottom to minimize damage to the bearing
surface from weather or construction activities. Water should not be allowed to pond in any
excavation.
6.4 Structural Fill Placement and Compaction
Fill materials for may consist of the non -organic on -site soils, or an off -site borrow having a
classification of CL or more granular. Controlled structural fill should be free of boulders, organic
matter, debris, or other deleterious materials, should have a maximum particle size of no greater
than 4 inches, and should have a maximum dry density, as determined by the standard proctor
test (ASTM D 698), of at least 90 pcf. As previously mentioned in Section 5.4, additional
restrictions will apply for the backfill materials behind below grade walls.
Stanley Martin Homes
F&R File No. 71Z0001
Page - 12 -
Pleasant Green Connector Road Culvert
January22, 2021
Based on our visual classifications and the laboratory test results, we anticipate that the on -site
soils should serve satisfactorily as fill provided that the moisture contents can be maintained
within acceptable limits. The on -site soils are considered moisture sensitive and maybe difficult
to work with when they are wet of the optimum moisture content. Based on our visual
examination and the laboratory test results, the soil samples were above their anticipated
moisture content. Therefore, drying of the on -site soils should be anticipated.
Predicated on the boring and laboratory results, and the recommendations provided above, the
best time for construction of the structural fills and compacted subgrades would be during the
warmer, drier months of the year, such as from late April through early October. During this time
frame, on -site soils that are wet of optimum can usually be dried to near optimum levels with
relatively little effort. If grading is performed during the colder, wetter months of the year, such
as late October through early April, and suitable dry materials are not available on -site, then off -
site drier borrow sources will likely be necessary.
Fill materials should be placed in horizontal lifts with a maximum loose lift thickness of 8 inches.
New fill should be adequately keyed into stripped and scarified subgrade soils. The fill should be
compacted to at least 95 percent of the material's maximum dry density as determined by the
standard Proctor method (ASTM D 698). In confined areas, portable compaction equipment and
thin lifts of 3 to 4 inches may be required to achieve specified degrees of compaction. Excessively
wet or dry soils should not be used as fill materials without proper drying or wetting. We
recommend a moisture content range of plus or minus 3 percentage points of the material's
optimum moisture content. We recommend that the contractor have equipment on site during
earthwork for both drying and wetting of fill soils.
Where construction traffic or weather has disturbed the subgrade, the upper 8 inches of soils
intended for structural support should be scarified and re -compacted. Field density tests to
determine the degree of compaction should be performed on each lift of fill, with a minimum of
two tests per lift.
6.5 Surface Water/Groundwater Control
Subsurface water for the purposes of this report is defined as water encountered below the
existing ground surface. Based on the subsurface water readings obtained during our exploration
program, we anticipate that subsurface water will be encountered during excavation for the
foundation of the box culverts. Therefore, the contractor should be prepared to dewater should
water levels vary from those encountered during the drilling program. Fluctuations in subsurface
water levels and soil moisture can be anticipated with changes in precipitation, runoff, and
season.
Stanley Martin Homes
F&R File No. 71Z0001
Page - 13 -
Pleasant Green Connector Road Culvert
January22, 2021
C
An important aspect to consider during development of this site is surface water control. During
the construction, we recommend that steps be taken to enhance surface flow away from any
excavations and promote rapid clearing of rainfall and runoff water following rain events. It
should be incumbent on the contractor to maintain favorable site drainage during construction
to reduce deterioration of otherwise stable subgrades.
6.6 Temporary Excavation Recommendations
Mass excavations and other excavations required for construction of this project must be
performed in accordance with the United States Department of Labor, Occupational Safety and
Health Administration (OSHA) guidelines (29 CFR 1926, Subpart P, Excavations) or other
applicable jurisdictional codes for permissible temporary side -slope ratios and/or shoring
requirements. The OSHA guidelines require daily inspections of excavations, adjacent areas and
protective systems by a "competent person" for evidence of situations that could result in cave-
ins, indications of failure of a protective system, or other hazardous conditions. All excavated
soils, equipment, building supplies, etc., should be placed away from the edges of the excavation
at a distance equaling or exceeding the depth of the excavation. F&R cautions that the actual
excavation slopes will need to be evaluated frequently each day by the "competent person" and
flatter slopes or the use of shoring may be required to maintain a safe excavation depending
upon excavation specific circumstances. The contractor is responsible for providing the
"competent person" and all aspects of site excavation safety. F&R can evaluate specific
excavation slope situations if we are informed and requested by the owner, designer or
contractor's "competent person".
Stanley Martin Homes
F&R File No. 71Z0001
Page -14-
Pleasant Green Connector Road Culvert
January22, 2021
X
7.0 CONTINUATION OF SERVICES
We recommend that we be given the opportunity to review the foundation plan, grading plan,
and project specifications when construction documents approach completion. This review
evaluates whether the recommendations and comments provided herein have been understood
and properly implemented. We also recommend that Froehling & Robertson, Inc. be retained
for professional and construction materials testing services during construction of the project.
Our continued involvement on the project helps provide continuity for proper implementation
of the recommendations discussed herein.
The Geotechnical Engineer of Record should be retained to monitor and test earthwork activities,
and subgrade preparations for foundations, excavations and floor slabs. It should be noted that
the actual soil conditions at the various subgrade levels and footing bearing grades will vary
across this site and thus the presence of the Geotechnical Engineer and/or his representative
during construction will serve to validate the subsurface conditions and recommendations
presented in this report. We recommend that F&R be employed to monitor the earthwork and
foundation construction, and to report that the recommendations contained in this report are
completed in a satisfactory manner. Our involvement on the project will aid in the proper
implementation of the recommendations discussed herein. The following is a recommended
scope of services:
• Review of project plans and construction specifications to verify that the
recommendations presented in this report have been properly interpreted and
implemented;
• Observe all foundation excavations and footing bearing grades for compliance with the
geotechnical recommendations.
• Observe and test bedding material and backfill for the box culvert.
These services are not included in our current scope of services and can be rendered for an
additional cost.
Stanley Martin Homes
F&R File No. 71Z0001
Page - 15 -
Pleasant Green Connector Road Culvert
January22, 2021
X
8.0 LIMITATIONS
This report has been prepared for the exclusive use of Stanley Martin Homes or their agent, for
specific application to the Pleasant Green Connector Road Culvert project, in accordance with
generally accepted soil and foundation engineering practices. No other warranty, express or
implied, is made. Our evaluations and recommendations are based on design information
furnished to us; the data obtained from the previously described subsurface exploration
program, and generally accepted geotechnical engineering practice. The evaluations and
recommendations do not reflect variations in subsurface conditions which could exist
intermediate of the boring locations or in unexplored areas of the site. Should such variations
become apparent during construction, it will be necessary to re-evaluate our recommendations
based upon on -site observations of the conditions.
There are important limitations to this and all geotechnical studies. Some of these limitations
are discussed in the information prepared by GBA, which is included in Appendix III. We ask that
you please review this GBA information.
Regardless of the thoroughness of a subsurface exploration, there is the possibility that
conditions between borings will differ from those at the boring locations, that conditions are not
as anticipated by the designers, or that the construction process has altered the soil conditions.
Therefore, experienced geotechnical engineers should evaluate earthwork, pavement, and
foundation construction to verify that the conditions anticipated in design actually exist.
Otherwise, we assume no responsibility for construction compliance with the design concepts,
specifications, or recommendations.
In the event that changes are made in the design or location of the proposed structure, the
recommendations presented in the report shall not be considered valid unless the changes are
reviewed by our firm and conclusions of this report modified and/or verified in writing. If this
report is copied or transmitted to a third party, it must be copied or transmitted in its entirety,
including text, attachments, and enclosures. Interpretations based on only a part of this report
may not be valid.
Stanley Martin Homes
F&R File No. 71Z0001
Page - 16 -
Pleasant Green Connector Road Culvert
January22, 2021
APPENDIX I
FROEHLING & ROBERTSON, INC.
Engineering Stability Since 1881
IF K 6185 Rockfish Gap Turnpike
Crozet, Virginia 22932-3330
T 434.823.5154 1 F 434.823.4764
Site Location Plan
Client: Stanley Martin Homes
Project: Pleasant Green Connector Road Culvert
F&R Project No. 71Z0001
Date: January 2021 1 Scale: No Scale I Drawing No.: 1
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Drawing No.
2
APPENDIX II
KEY TO BORING LOG SOIL CLASSIFICATION
Particle Size and Proportion
Verbal descriptions are assigned to each soil sample or stratum based on estimates of the
particle size of each component of the soil and the percentage of each component of the soil.
Particle Size
Proportion
Descri tive Terms
Descriptive Terms
Soil Component
Particle Size
Component
Term
Percentage
Boulder
> 12 inch
Major
Uppercase Letters
>50%
Cobble
3 — 12 inch
(e.g., SAND, CLAY)
Gravel -Coarse
1/4 - 3 inch
-Fine
#4 - 3/4 inch
Secondary
Adjective
20%-50%
Sand -Coarse
#10 - #4
(e.g. sandy, clayey)
-Medium
#40 - # 10
-Fine
#200 - 440
Minor
Some
15%-25%
Silt(non-cohesive)<#200
Little
5%-15%
Clay (cohesive)
<#200
Trace
0%-5%
Notes:
1. Particle size is designated by U.S. Standard Sieve Sizes
2. Because of the small size of the split spoon sampler relative to the size of gravel, the true percentage of gravel may
not be accurately estimated.
Density or Consistency
The standard penetration resistance values (N-values are used to describe the density of
coarse -grained soils (GRAVEL, SAND) or the consistency of fine-grained soils (SILT, CLAY).
Sandy silts of very low plasticity may be assigned a density instead of a consistency.
DENSITY
CONSISTENCY
Term
N-Value
Term
N-Value
Very Loose
0-4
Very Soft
0-1
Loose
5 — 10
Soft
2-4
Medium -Dense
11— 30
Medium Stiff
5-8
Dense
31— 50
Stiff
9 — 15
Very Dense
> 50
Very Stiff
16 — 30
Hard
>30
Notes:
1. The N-value is the number of blows of a 140 lb. hammer freely falling 30 inches required to drive a standard split -
spoon sampler (2.0 in. O.D., 1-3/8 in. I.D.) 12 inches into the soil after properly seating the sampler 6 inches.
2. When encountered, gravel may increase the N-value of the standard penetration test and may not accurately
represent the in -situ density or consistency of the soil sampled.
CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES
ASTM Designation: D 2487
(Based on Unified Soil Classification System)
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests"
Soil Classification
Group Symbol
Group Name
COARSE -GRAINED
Gravels
Clean Gravels
Cu a and 15 Cc53`
GW
Well graded gravel`
SOILS
More than 50%
Less than 5%fines`
Cu<4 and/or 1>Cc>3
GP
Poorly graded gravel
More than 50%
coarse fraction
Gravels with Fines
Fines classify as MIL or MH
GM
Silty gravel r'1,H
retained on No. 200
retaining on No. 4
More than 12 %fines`
Fines classify as CL or CH
Clayey gravel ' '
GC
sieve
sieve
Sands
Clean Sands
Cu t 6 and 15 Cc 53 r
SW
Well -graded sand'
50% or more of
Less than 5%fines°
Cu<6 and/or 1>Cc>3r
SP
Poorly graded sand'
coarse fraction
Sands with Fines
Fines classify as MIL or MH
SM
Siltysand "
passes No.4 sieve
More than 12%fines°
Fines classify as CL or CH
SC
Clayey sand°'"''
FINE-GRAINED SOILS
Silts and Clays
Inorganic
PI> 7 and plots on or above
Lean clay'
CL
50% or more passes
Liquid Limit less than
"A" line'
the No. 200 sieve
50
PI <4 or plots below "A" line'
MIL
slit""'
Organic
Liquid limit- ovendried<0.75
Organic clay"'`'°''"
OL
Organic silt' '
Liquid limit - not dried
Silts and Clays
Inorganic
PI plots on or above "A" line
CH
Fat clayK "m
Liquid Limit 50 or
PI plots below "A" line
MH
Elastic silt""'"'
more
Organic
Liquid limit- ovendried<0.75
Organic clay
Liquid limit - not dried
OH
Organic silt
HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor
PT
Peat
A
Based on the material passing the 3-in (75 mm) sieve
E
Cu=D60/010 Cc= (030)�/(010a060)
J
If Atterberg limits plot in hatched area, soils is a CL-ML,
8
If field sample contained cobbles or boulders, or both,
add
F
If soil contains 2 15% sand, add "with sand" to the
silty clay
"with cobbles or boulders, or both" to group name.
group name
K
If soil contains 15 to 29%plus No. 200, add "with sand" or
C
Gravels with 5 to12% fines require dual symbols:
G
If fines classify as CL-NI use dual symbol GC -GM, or
"with gravel," whichever is predominant
G W-GM well -graded gravel with silt
SC-SM
L
If soil contains 2 30% plus No. 200, predominantly sand,
GW-GC well -graded gravel with clay
H if fines are organic, add "with organic fines" to the
add "sandy" to group name
GP -GM poorly graded gravel with silt
group name
M
If sail contains 2 30%plus Na. 200, predominantly gravel,
GP -GC poorly graded gravel with clay
D
Sands with 5 to 12%fines require dual symbols:
If soil contains 215%gravel, add "with gravel" to
add "gravelly" to group name
N
SW-SM well -graded sand with silt
group name
PI 2 4 and plots on or above "A" line
SW -SC well -graded sand with clay
O
PI < 0 or plots below "A"line
SP-SM poorly graded sand with silt
P
PI plots on or above "A" line
SP-SC poorly graded sand with clay
° PI plots below "A" line
0
SIEVE ANALYSIS
Screen (in) Sieve No.
1.5 % 4 10 10 40 W 100 200
MIMIMM
I
10 1 0.1 0.01
Panicle a..1.1
Cu = D60/DIO = (3/0.2) =15
Cc = (D30)'/(D10a060) = (0.62)/(0.2'3) = 0.6
For classification of fine-grained soils and fine-grained fraction of coarse -grained soils:
W
50
40
Plasticity Index IN)
30
20
30
0
0
10 20 30 40 50 0 70 90 90 100 110
Liquid Limit ILL)
Equation of "A" line: Horizontal at PI = 4 to LL= 22.5, then PI = 0.73'(IL-20)
Equation of "U" line: vertical at ILL =16 to PI = 7, then PI = 0.9'(LL-8)
SOIL CLASSIFICATION CHART
MAJOR DIVISIONS
SYMBOLS TYPICAL
GRAPH LETTER DESCRIPTIONS
GRAVEL
AND
CLEAN
GRAVELS
I'. .06.
61w.:
GW
WELL -GRADED GRAVELS, GRAVEL -
SAND MIXTURES, LITTLE OR NO
FINES
GRAVELLY
SOILS
(LITTLE OR NO FINES)
oQ°
o DOo D
O 00
GP
POORLY -GRADED GRAVELS,
GRAVEL - SAND MIXTURES, LITTLE
OR NO FINES
COARSE
GRAINED
SOILS
MORE THAN 50%
OF COARSE
FRACTION
GRAVELS WITH
FINES
D
3
0
°c
01
D
O
GM
SILTY GRAVELS, GRAVEL -SAND -
SILT MIXTURES
RETAINED ON NO.
4 SIEVE
(APPRECIABLE
AMOUNT OF FINES)
GC
CLAYEY GRAVELS, GRAVEL - SAND -
CLAY MIXTURES
MORE THAN 50%
OF MATERIAL IS
SAND
AND
CLEAN SANDS
SW
WELL -GRADED SANDS, GRAVELLY
SANDS, LITTLE OR NO FINES
�:
SIP
POORLY -GRADED SANDS,
GRAVELLY SAND, LITTLE OR NO
FINES
LARGER THAN
NO. 200SIEVE
SIZE
SANDY
SOILS
(LITTLE OR NO FINES)
SANDS WITH
FINES
S.M
SILTY SANDS, SAND - SILT
MIXTURES
MORE THAN 50%
OF COARSE
FRACTION
PASSING ON NO.
4 SIEVE
(APPRECIABLE
AMOUNT OF FINES)
SC
CLAYEY SANDS, SAND - CLAY
MIXTURES
INORGANIC SILTS AND VERY FINE
ML
SANDS, ROCK FLOUR, SILTY OR
CLAYEY FINE SANDS OR CLAYEY
SILTS WITH SLIGHT PLASTICITY
CL
INORGANIC CLAYS OF LOW TO
MEDIUM PLASTICITY, GRAVELLY
CLAYS, SANDY CLAYS, SILTY
CLAYS, LEAN CLAYS
FINE
GRAINED
SOILS
SILTS
AND LIQUID LIMIT
CLAYS LESS THAN 50
— —
OL
ORGANIC SILTS AND ORGANIC
SILTY CLAYS OF LOW PLASTICITY
MORE THAN 50%
OF MATERIAL IS
SMALLER THAN
NO. 200 SIEVE
MH
INORGANIC SILTS, MICACEOUS OR
DIATOMACEOUS FINE SAND OR
SILTY SOILS
SIZE
SILTS
AND LIQUID LIMIT
CLAYS GREATER THAN 50
CH
INORGANIC CLAYS OF HIGH
PLASTICITY
OH
ORGANIC CLAYS OF MEDIUM TO
HIGH PLASTICITY, ORGANIC SILTS
EXISTING FILL
FILL
EXISTING FILL MATERIALS
NOTE: DUAL SYMBOLS ARE USED TO INDICATE BORDERLINE SOIL CLASSIFICATIONS
SINCE
nro9.D Fir oehl ing & Robertson, Inc.
BORING LOG
1BBI
Project No: 71Z0001 Elevation: 693 ±
Client: Stanley Martin Homes Total Depth: 22.2'
Project: Pleasant Green Connector Road Culvert
City/State: Albemarle County, Virginia Boring Location: See Boring Location Plan
Boring: B-01 (1 of 1)
Drilling Method: HSA
Hammer Type: Automatic
Date Drilled: 1/7/21
Driller: SDS
Elevation
Depth
Description of Materials
(Classification)
` Sample
Blows
Sample
Depth
feet
N-Value
(blows /ft)
Remarks
692.7
0.3
SurficialOrganics
-1
3
Brown, Very Moist, Very Loose, Silty SAND (SM),
Trace Gravel
691.0
2.0
ALLUVIUM
2.0
Brown, Wet, Very Loose, Silty SAND (SM), Little
2-1-50 2
690.0
3.0
Gravel
ALLUVIUM
3.2
100+
689.0
4.0
...
Brown, Wet, Very Dense, Silty GRAVEL (GM),
Little Sand
4.0
9-12-12
4
ALLUVIUM
-50/1
24
Subsurface water
Brown, VeryMoist, Medium Dense, Silty SAND
tY
(SM), Some Gravel
5.6
encountered at 5 feet
687.0
6.0
ALLUVIUM
6.0
2
below existing grades
following removal of the
augers.
2-1-1
-2
Brown, Wet, Soft, Sandy SILT (ML)
RESIDUUM
685.0
8.0
8.0
6
Brown and Tan, Wet, Very Loose to Medium
Dense, Silty SAND (SM)
6-2-4
-4
RESIDUUM
10.0
Cave-in depth recorded at
12 feet below existing
grades upon removal of
13.5
the augers.
3-6 12
18
15.0
18.5
2-1-3
4
20.0
670.8
67.
22.0
22.2
22.0
Soft Weathered Rock becomes Gray, Wet, Very
Dense, Silty GRAVEL (GM), Little Sand
50 2
100+
SOFT WEATHERED ROCK
Auger Refusal at 22 Feet
'Number or Mows required Tor a 14u It) hammer dropping 310'to drive Z' U.D., 1.3/5" I.U. sampler a Total or 16 inches In three V increments.
The sum of the second and third increments of penetration is termed the standard penetration resistance, N-Value.
SINCE
nro9.D Fir oehl ing & Robertson, Inc.
BORING LOG
,sB,
Project No: 71Z0001 Elevation: 691±
Client: Stanley Martin Homes Total Depth: 5.4'
Project: Pleasant Green Connector Road Culvert
City/State: Albemarle County, Virginia Boring Location: See Boring Locaiton Plan
Boring: B-02 (1 of 1)
Drilling Method: HSA
Hammer Type: Automatic
Date Drilled: 1/7/21
Driller: SDS
Elevation
Depth
Description of Materials
` Sample
Sample
Depth
N-Value
(blows /ft)
Remarks
(Classification)
Blows
feet
690.7
0.3
SurficialOrganics
2-2-2
2
4
Tan Brown, Very Moist, Soft, Sandy SILT (ML)
ALLUVIUM
689.0
2.0
4
2.0
Subsurface water
Tan Brown, Very Moist, Medium Stiff, Sandy
2-2-3
-
Lean CLAY (CL)
-5
5
encountered at 2.5 feet
ALLUVIUM
below existing grades
following removal of the
687.0
4.0
4.0
augers.
Gray, Wet, Medium Dense, Silty GRAVEL (GM),
5-10-12
Little Sand
-13
22
685.E
5.4
ALLUVIUM
Auger Refusal at 5.4 Feet
6.0
Cave-in depth recorded at
3 feet below existing
grades upon removal of
the augers.
An offset boring 8 feet
west of B-02 encountered
refusal at 5.4 feet below
existing grades.
'Number or blows required Tor a 14u It) hammer dropping 310'to drive Z' U.D., 1.3/5" I.U. Sampler a Total or 16 inches In three V increments.
The sum of the second and third increments of penetration is termed the standard penetration resistance, N-Value.
SINCE
f&�i Froehl ing & Robertson, Inc.
1681 `
Project No: 71Z0001
Client: Stanley Martin Homes
Project: Pleasant Green Connector Road Culvert
City/State: Albemarle County, Virginia
SUBSURFACE PROFILE
Plot Based on Elevation
Profile Name: Subsurface Profile
694
B-01
3
B-02
50/2
4
690
......................:.............................................
................:.....................:.....................:.............................................
................:..................................
24 Q
5
688
...............................................................7
X.............:...............
Approximate. Invert .Elevation........................:...
.............. ................ .....
2
22
686
.....................................................................
............................................................................................................
..................................................
6
c
684
:.:
............... ................ ................ ................ ................ .....
0
a
680
..:
: .............. .....
18
678
a
a
m
i7
0
0
674
.....................
:.4..............................................................................
................ ................ ................ .....
x
ro
'a
i
50/2
5
670
APPENDIX III
— Geolechnicol-Engineeping Report —,
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you - assumedly
a client representative - interpret and apply this
geotechnical-engineering report as effectively
as possible. In that way, clients can benefit from
a lowered exposure to the subsurface problems
that, for decades, have been a principal cause of
construction delays, cost overruns, claims, and
disputes. If you have questions or want more
information about any of the issues discussed below,
contact your GBA-member geotechnical engineer.
Active involvement in the Geoprofessional Business
Association exposes geotechnical engineers to a
wide array of risk -confrontation techniques that can
be of genuine benefit for everyone involved with a
construction project.
Geotechnical-Engineering Services Are Performed for
Specific Purposes, Persons, and Projects
Geotechnical engineers structure their services to meet the specific
needs of their clients. A geotechnical-engineering study conducted
for a given civil engineer will not likely meet the needs of a civil -
works constructor or even a different civil engineer. Because each
geotechnical-engineering study is unique, each geotechnical-
engineering report is unique, prepared solely for the client. Those who
rely on a geotechnical-engineering report prepared for a different client
can be seriously misled. No one except authorized client representatives
should rely on this geotechnical-engineering report without first
conferring with the geotechnical engineer who prepared it. And no one
- not even you - should apply this report for any purpose or project except
the one originally contemplated.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read it in its entirety. Do not rely on an
executive summary. Do not read selected elements only. Read this report
in full.
You Need to Inform Your Geotechnical Engineer
about Change
Your geotechnical engineer considered unique, project -specific factors
when designing the study behind this report and developing the
confirmation -dependent recommendations the report conveys. A few
typical factors include:
• the client's goals, objectives, budget, schedule, and
risk -management preferences;
• the general nature of the structure involved, its size,
configuration, and performance criteria;
• the structure's location and orientation on the site; and
• other planned or existing site improvements, such as
retaining walls, access roads, parking lots, and
underground utilities.
Typical changes that could erode the reliability of this report include
those that affect:
• the site's size or shape;
• the function of the proposed structure, as when it's
changed from a parking garage to an office building, or
from a light -industrial plant to a refrigerated warehouse;
• the elevation, configuration, location, orientation, or
weight of the proposed structure;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
changes - even minor ones - and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
This Report May Not Be Reliable
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project;
• for a different site (that may or may not include all or a
portion of the original site); or
• before important events occurred at the site or adjacent
to it; e.g., man-made events like construction or
environmental remediation, or natural events like floods,
droughts, earthquakes, or groundwater fluctuations.
Note, too, that it could be unwise to rely on a geotechnical-engineering
report whose reliability may have been affected by the passage of time,
because of factors like changed subsurface conditions; new or modified
codes, standards, or regulations; or new techniques or tools. If your
geotechnical engineer has not indicated an apply -by" date on the report,
ask what it should be, and, in general, if you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying it. A minor amount of additional testing or
analysis - if any is required at all - could prevent major problems.
Most of the "Findings" Related in This Report Are
Professional Opinions
Before construction begins, geotechnical engineers explore a site's
subsurface through various sampling and testing procedures.
Geotechnical engineers can observe actual subsurface conditions only at
those specific locations where sampling and testing were performed. The
data derived from that sampling and testing were reviewed by your
geotechnical engineer, who then applied professional judgment to
form opinions about subsurface conditions throughout the site. Actual
sitewide-subsurface conditions may differ - maybe significantly - from
those indicated in this report. Confront that risk by retaining your
geotechnical engineer to serve on the design team from project start to
project finish, so the individual can provide informed guidance quickly,
whenever needed.
This Report's Recommendations Are
Confirmation -Dependent
The recommendations included in this report - including any options
or alternatives - are confirmation -dependent. In other words, they are
not final, because the geotechnical engineer who developed them relied
heavily on judgment and opinion to do so. Your geotechnical engineer
can finalize the recommendations only after observing actual subsurface
conditions revealed during construction. If through observation your
geotechnical engineer confirms that the conditions assumed to exist
actually do exist, the recommendations can be relied upon, assuming
no other changes have occurred. The geotechnical engineer who prepared
this report cannot assume responsibility or liabilityfor confirmation -
dependent recommendations if you fail to retain that engineer to perform
construction observation.
This Report Could Be Misinterpreted
Other design professionals' misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a full-time member of the
design team, to:
• confer with other design -team members,
• help develop specifications,
• review pertinent elements of other design professionals'
plans and specifications, and
• be on hand quickly whenever geotechnical-engineering
guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction
observation.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated -subsurface -conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you've included the material for informational
purposes only. To avoid misunderstanding, you may also want to note
that "informational purposes" means constructors have no right to rely
on the interpretations, opinions, conclusions, or recommendations in
the report, but they may rely on the factual data relative to the specific
times, locations, and depths/elevations referenced. Be certain that
constructors know they may learn about specific project requirements,
including options selected from the report, only from the design
drawings and specifications. Remind constructors that they may
perform their own studies if they want to, and be sure to allow enough
time to permit them to do so. Only then might you be in a position
to give constructors the information available to you, while requiring
them to at least share some of the financial responsibilities stemming
from unanticipated conditions. Conducting prebid and preconstruction
conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. That lack of understanding has nurtured
unrealistic expectations that have resulted in disappointments, delays,
cost overruns, claims, and disputes. To confront that risk, geotedmical
engineers commonly include explanatory provisions in their reports.
Sometimes labeled "limitations;' many of these provisions indicate
where geotechnical engineers responsibilities begin and end, to help
others recognize their own responsibilities and risks. Read these
provisions closely. Ask questions. Your geotechnical engineer should
respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study - e.g., a "phase -one" or "phase -two" environmental
site assessment - differ significantly from those used to perform
a geotechnical-engineering study. For that reason, a geotechnical-
engineering report does not usually relate any environmental findings,
conclusions, or recommendations; e.g., about the likelihood of
encountering underground storage tanks or regulated contaminants.
Unanticipated subsurface environmental problems have led to project
failures. If you have not yet obtained your own environmental
information, ask your geotechnical consultant for risk -management
guidance. As a general rule, do not rely on an environmental report
prepared for a different client, site, or project, or that is more than six
months old.
Obtain Professional Assistance to Deal with Moisture
Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, none of the engineer's
services were designed, conducted, or intended to prevent uncontrolled
migration of moisture - including water vapor - from the soil through
building slabs and walls and into the building interior, where it can
cause mold growth and material -performance deficiencies. Accordingly,
proper implementation of the geotechnical engineer's recommendations
will not of itself be sufficient to prevent moisture infiltration. Confront
the risk of moisture infiltration by including building -envelope or mold
specialists on the design team. Geotechnical engineers are not building -
envelope or mold specialists.
GEOPROFESSIONAL
BUSINESS
&RA ASSOCIATION
Telephone: 301/565-2733
e-mail: info@geoprofessional.org www.geoprofessional.org
Copyright 2016 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with Gags specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written pern Isom
ofGBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element ofa report of any
kind. Any other for, individual, or other entity that so uses this document without being a GBA member could be committing negligent