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REPORT OF PRELIMINARY GEOTECHNICAL SUBSURFACE EXPLORATION
7TH STREET APARTMENTS 705 EAST 7TH STREET CHARLOTTE, NORTH CAROLINA
SUMMIT PROJECT NO. PROJECT 4164.11
Prepared For:
Mr. Andrew Miller Laurel Street Residential 511 East Boulevard Charlotte, North Carolina 28203
Email: Amiller@laurelstreetres.com
Prepared By: SUMMIT Engineering, Laboratory & Testing, P. C. (SUMMIT)
3575 Centre Circle Drive Fort Mill, South Carolina 29715 December 10, 2019
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11 7th Street Apartments December 10, 2019
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TABLE OF CONTENTS
SECTION Page
EXECUTIVE SUMMARY ........................................................................................................... iii 1.0 INTRODUCTION .............................................................................................................. 1 1.1. Site and Project Description.................................................................................... 1
1.2. Purpose of preliminary Subsurface Exploration ..................................................... 1
2.0 EXPLORATION PROCEDURES...................................................................................... 3 2.1. Field Exploration .................................................................................................... 3 3.0 AREA GEOLOGY AND SUBSURFACE CONDITIONS ............................................... 4 3.1. Physiography and Area Geology ............................................................................ 4
3.2. Generalized Subsurface Stratigraphy ...................................................................... 4
3.2.1. Surface Materials........................................................................................ 5 3.2.2. Existing Fill Soils ....................................................................................... 5 3.2.3. Residual Soils ............................................................................................. 6 3.2.4. Partially Weathered Rock and Auger Refusal............................................ 7
3.2.5. Groundwater Level Measurements ............................................................ 8
4.0 PRELIMINARY RECOMMENDATIONS........................................................................ 9 4.1. General .................................................................................................................... 9 4.2. Foundation Recommendations................................................................................ 9 4.2.1. Shallow Foundation System bearing on New Structural fill .................... 10
4.2.2. Shallow Foundation System bearing on Deep Foundation System ......... 11
4.2.3. Post Tension Slab System Discussions: ................................................... 14 4.3. Seismic Site Class ................................................................................................. 14 4.4. Low to Moderate Plasticity Moisture Sensitive Soils (CL and MH) .................... 15 4.5. Wet Weather Conditions ....................................................................................... 15
4.6. Floor Slabs ............................................................................................................ 16
4.7. Pavements Subgrade Preparation .......................................................................... 16 4.8. Cut and Fill Slopes ................................................................................................ 17 5.0 CONSTRUCTION CONSIDERATIONS ........................................................................ 18 5.1. Abandoned Utilities/Structures ............................................................................. 18
5.2. Site Preparation ..................................................................................................... 18 5.3. Difficult Excavation .............................................................................................. 19 5.4. Temporary Dewatering ......................................................................................... 20 5.5. Temporary Excavation Stability ........................................................................... 21 5.6. Structural Fill ........................................................................................................ 22
5.7. Engineering Services During Construction .......................................................... 23 6.0 RELIANCE AND QUALIFICATIONS OF REPORT .................................................... 24
APPENDIX 1 - Figures
Site Vicinity Map (Figure 1) Boring Location Plan (Figure 2)
APPENDIX 2 – Subsurface Diagram and Boring Logs
APPENDIX 3 – ReMi Test Results
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11 7th Street Apartments December 10, 2019
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EXECUTIVE SUMMARY
SUMMIT has completed a preliminary geotechnical subsurface exploration for the 7th Street
Apartments project. The purpose of this exploration was to obtain general information regarding the subsurface conditions and to provide geotechnical recommendations regarding foundation support of the proposed construction. The exploration consisted of seven (7) soil test borings (identified as B-1 through B-6 and BMP-1). The approximate test locations are shown on Figure 2 provided in Appendix 1. The following geotechnical engineering information was obtained as a
result of the soil test borings:
• Surface Materials – Surficial organic (topsoil) soils were observed at the existing ground surface of Borings B-1 through B-6 with thickness of approximately 4 inches. Boring BMP-1 encountered an approximate 8-inch layer of asphalt pavement underlain with an approximate
4-inch layer of stone aggregate.
• Existing Fill Soils - Existing fill (disturbed) soils were encountered beneath the surface materials in Borings B-1 through B-6 and BMP-1 to approximate depths ranging from 3 to 17 feet below the existing ground surface. When sampled, the existing fill soils generally
consisted elastic silts (MH), sandy silts (ML), and silty sands (SM). Please note that organic
stained fill soils were encountered in Borings B-5 and B-6, and construction debris was encountered in Boring B-3 from 5.5 up to 13 feet. The Standard Penetration Resistances (SPT N-values) in the existing fill soils ranged from 3 to 36 blows per foot (bpf).
• Residual Soils - Residual (undisturbed) soils were encountered below the surface materials
and/or existing fill soils in Borings B-4 and BMP-1, and extended to either the maximum termination depth or partially weathered rock (PWR). These residual soils generally consisted of lean clays (CL), elastic silts (MH), sandy silts (ML), and silty sands (SM). The Standard Penetration Resistances (SPT N-values) in the residual soils ranged from 5 to 55 bpf.
• Partially Weathered Rock (PWR) and Auger Refusal – Partially weathered rock (PWR)
conditions were encountered in Borings B-1, B-2, B-4, B-5 and B-6 at approximate depths ranging from 5.5 to 17 feet below the existing ground surface. Auger refusal conditions were encountered in Borings B-1 through B-6 at approximate depths ranging from 7.3 to 22.4 feet below the existing ground surface. Please note that auger refusal was encountered in Boring
B-3 on unknown material (possible building debris).
• Groundwater Levels - At the time of drilling, groundwater levels were observed in Borings B-3, B-4 and B-6 at approximate depths of 10.2, 7.3 and 6.8 feet below the existing ground surface, respectively. After waiting more than 24 hours, water levels were observed in Borings
B-3 and B-4 at approximate depths of 10.2 and 4.2 feet, respectively.
• Foundation Support - Based on the results of our borings and estimated building loads, the proposed structures cannot be adequately supported on shallow foundations bearing on the existing conditions due variable and/or unsuitable soils and construction debris without exceeding an acceptable amount of differential settlements of the foundations due to the
consolidation of the underlying soils and debris. We have provided options for support of the
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proposed building foundation system which consist of 1) shallow foundation system bearing
on new structural fill, or 2) a deep foundation system such as Drilled Shafts (“piers or
caissons”) or Rammed Aggregate Piers, or 3) support the proposed structure on a Post Tension (PT) slab system.
• Seismic Site Class – We have determined the Seismic Site Classification for this project site in accordance with Chapter 16, Section 1613.5.2 of the 2012 North Carolina Building Code,
Site Class Definitions using Soil Shear Wave Velocity. We recommend this project be designed using a Seismic Site Class of “C” (Very Dense Soil and Soft Rock) having an average shear wave velocity of 2,765 ft/sec and soil greater than 10 feet between the rock surface and project bottom of the spread footing or matt foundation as defined in Table 1613.5.4 Site Class Definitions.
• Special Construction Considerations: Special considerations are warranted concerning existing fill soils, organic stained/laden soils, construction debris, soils with SPT N-values less than 7 bpf, removal of PWR and auger refusal materials, shallow groundwater levels, and existing pipe/culvert that crosses the site. The following summarizes our understandings and
recommendations.
o Existing Fill Soils: At the time of this report, no relevant information (documentations) regarding previous grading activities, prior materials testing, and/or geotechnical engineering services was provided for our review. All of the borings encountered undocumented fill soils (fill soils not monitored and tested during placement) and
undocumented fill poses risks associated with undetected deleterious materials within the fill soils and/or deleterious material at the interface between the fill soils and residual soils.
o Organic Stained and/or Laden Soils and Construction Debris: Organic stained soils were encountered in Borings B-5 and B-6 at various depths, and debris laden fills and/or debris were encountered in Borings B-3, B-5 and B-6 at various depths. These materials are
considered not suitable for building and pavement support and are not suitable to be re-used as structural fill material.
o Soils with SPT N-values less than bpf7: Soils that exhibited SPT N-values less than 7 bpf are considered not suitable to support the proposed construction. The soil conditions were generally encountered in Borings B-1, B-3 and BMP-1 at various depths.
o Difficult Excavation: The result of the borings indicated that the excavation of residual soils is possible with conventional excavating techniques. However, please note that partially weathered rock (PWR) conditions were encountered in five (5) of the borings and auger refusal conditions were encountered in six (6) of the borings performed for this exploration. Dependent on final grades and locations, the contractor should anticipate the
excavations of PWR and auger refusal conditions will require specialized equipment and procedures.
o Shallow Groundwater: At the time of drilling, groundwater levels were observed in Borings B-3, B-4 and B-6 at approximate depths of 10.2, 7.3 and 6.8 feet below the existing ground surface, respectively. After waiting more than 24 hours, water levels were observed
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11 7th Street Apartments December 10, 2019
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in Borings B-3 and B-4 at approximate depths of 10.2 and 4.2 feet, respectively. Should
groundwater be encountered while performing excavations associated with the
construction, the contractor should be prepared to promptly remove/dewater the water from the general construction area. Pump(s) should remain on standby to handle groundwater as necessary.
Please note that the information provided in this executive summary is intended to be a brief
overview of project information and recommendations from the geotechnical report. The
information in the executive summary should not be used without first reading the geotechnical report in its entirety and the recommendations described therein.
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
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1.0 INTRODUCTION
1.1. Site and Project Description
The subject site is located at 705 East 7th Street in Charlotte, North Carolina. A vicinity map
showing the project’s general location is provided as Figure 1 provided in Appendix 1. The
subject property is approximately 1.21 acres comprised of Mecklenburg County Tax Parcel IDs
Number 08010402 and a portion of IDs Number 0801408. At the time of our field exploration, the
subject site consisted of two (2) structures, grass yard and an existing parking lot.
The Client (Laurel Street Residential) provided SUMMIT a plan sheet titled “Sketch Plan”,
prepared by Timmons Group dated July 9, 2019 that indicated the configurations of the proposed
construction planned for this project and the locations of the borings. Based on the provided
information, we understand the project is planned to include a 100-unit five-story Multi-Family
complex with associated pavements, and an underground stormwater retention.
At the time of report preparation, SUMMIT had not been provided structural details of the planned
construction indicating proposed loads, foundation bearing elevations, or finished floor elevations.
For this report, SUMMIT assumed the proposed structure will be supported on a shallow
foundation system consisting of spread, strip, and/or combined footings and that wall loads will
be on the order of 1 to 4 kips per foot and column loads on the order of 100 to 300 kips. Also,
grading plans were not available at the time of this report and we have assumed that maximum
cut/fill depths will be on the order of 1 to 3 feet over the existing ground surface.
1.2. Purpose of preliminary Subsurface Exploration
The purpose of this exploration was to obtain general geotechnical information regarding the
subsurface conditions and to provide general preliminary recommendations regarding the
geotechnical aspects of site preparation and foundation design. This report contains the following
items:
• General subsurface conditions,
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• Boring logs and an approximate “Boring Location Plan”,
• Suitable foundation types,
• Allowable bearing pressures for design of shallow foundations, (if applicable)
• Anticipated excavation difficulties during site grading and/or utility installation,
• Remedial measures to correct unsatisfactory soil conditions during site development, as
needed,
• Drainage requirements around structures and under floor slabs, as needed,
• Construction considerations,
• Pavement subgrade support guidelines,
• Seismic Site Classification.
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2.0 EXPLORATION PROCEDURES
2.1. Field Exploration
SUMMIT visited the site on November 6 and 7, 2019 and performed a preliminary subsurface
exploration that consisted of seven (7) soil test borings (identified as B-1 through B-6 and BMP-
1). The approximate locations of the borings are shown on the Figure 2 - “Boring Location Plan”
provided in Appendix 1. The borings were located by professionals from our office using the
provided plan, recreation-grade handheld GPS, existing topography, and aerial maps as reference.
Since the boring locations were not surveyed, the location of the borings should be considered
approximate. Also, the ground surface elevation provided on the Boring Logs were estimated from
Polaris 3G Map – Mecklenburg County web site.
The soil test borings were performed using a track-mounted Diedrich D50 drill rig and extended
to approximate depths of 7.3 to 22.4 feet below the existing ground surface. Hollow-stem,
continuous flight auger drilling techniques were used to advance the borings into the ground.
Standard Penetration Tests (SPT) were performed within the mechanical borings at designated
intervals in general accordance with ASTM D 1586. The SPT “N” value represents the number
of blows required to drive a split-barrel sampler 12 inches with a 140-pound hammer falling from
a height of 30 inches. When properly evaluated, the SPT results can be used as an index for
estimating soil strength and density. In conjunction with the penetration testing, representative
soil samples were obtained from each test location and returned to our laboratory for visual
classification in general accordance with ASTM D 2488. Water level measurements were
attempted at the termination of drilling. The results of these tests are presented on the individual
boring logs provided in Appendix 2 at the respective test depth.
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3.0 AREA GEOLOGY AND SUBSURFACE CONDITIONS
3.1. Physiography and Area Geology
The subject property is located in Charlotte, North Carolina, which is located in the south central
Piedmont Physiographic Province. The Piedmont Province generally consists of well-rounded
hills and ridges which are dissected by a well-developed system of draws and streams. The
Piedmont Province is predominantly underlain by metamorphic rock (formed by heat, pressure
and/or chemical action) and igneous rock (formed directly from molten material) which were
initially formed during the Precambrian and Paleozoic eras. The volcanic and sedimentary rocks
deposited in the Piedmont Province during the Precambrian era were the host of the metamorphism
and were generally changed to gneiss and schist. The more recent Paleozoic era had periods of
igneous emplacement, with episodes of regional metamorphism resulting in the majority of the
rock types seen today.
The topographic relief found throughout the Piedmont Province has developed from differential
weathering of theses igneous and metamorphic rock formations. Ridges developed along the more
easily weathered and erodible rock. Because of the continued chemical and physical weathering,
the rocks in the Piedmont Province are generally covered with a mantle of soil that has weathered
in-place from the parent bedrock below. These soils have variable thicknesses and are referred to
as residual soils, as they are the result of in-place weathering. Residual soils are typically fine-
grained and have a higher clay content near the ground surface because of the advanced
weathering. Similarly, residual soils typically become more coarse-grained with increasing depth
because of decreased weathering. As weathering decreases with depth, residual soils generally
retain the overall appearance, texture, gradation and foliations of their parent rock.
3.2. Generalized Subsurface Stratigraphy
General subsurface conditions observed during our geotechnical exploration are described herein.
For more detailed soil descriptions and stratifications at a particular field test location, the
respective “Boring Logs”, provided in Appendix 2 should be reviewed. The horizontal
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stratification lines designating the interface between various strata represents approximate
boundaries. Transitions between different strata in the field may be gradual in both the horizontal
and vertical directions. Therefore, subsurface stratigraphy between test locations may vary.
3.2.1. Surface Materials
Surficial organic (topsoil) soils were observed at the existing ground surface of Borings B-
1 through B-6 with thickness of approximately 4 inches. Boring BMP-1 encountered an
approximate 8-inch layer of asphalt pavement underlain with an approximate 4-inch layer
of stone aggregate.
3.2.2. Existing Fill Soils
Existing fill (disturbed soils were encountered beneath the surface materials in Borings B-
1 through B-6 and BMP-1 to approximate depths ranging from 3 to 17 feet below the
existing ground surface. When sampled, the existing fill soils generally consisted soft to
very stiff elastic silts (MH), soft to hard sandy silts (ML), and medium dense silty sands
(SM). The Standard Penetration Resistances (SPT N-values) in the existing fill soils
ranged from 3 to 36 blows per foot (bpf).
Please note organic stained soils were encountered in Borings B-5 and B-6 at various
depths, and debris laden fills and/or debris were encountered in Borings B-3, B-5 and B-6
at various depths. These materials are considered not suitable for building and pavement
support and are not suitable to be re-used as structural fill material.
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The following table summarizes the locations and approximate depths that existing fill soils
and unsuitable materials were encountered in the borings performed for this exploration.
Summary Table of Existing Fill Soils Depths
Boring No. Existing Fill Soil Approx. Depth, (feet)1 Unsuitable Soils/Materials Approx. Depth, (feet)1
B-1 9 Soft Fill Soils (5.5 to 9)
B-2 17 ---
B-3 5.5 Soft Fill Soils (0 to 3), Fill with Debris (3 to 5.5) & Debris (5.5 to 13)
B-4 3 ---
B-5 8.5 Organic Stain Soils (0 to 3) and Fills /w Debris (5.5 to 8.5)
B-6 8 Fills /w Debris (3 to 5.5) and Organic Stain Soils (5.5 to 8)
BMP-1 4 Soft Fill Soils (0 to 2) and Firm Fill soils (2 to 4)
1Depths were measured from the existing ground surface at the time drilling was performed.
Based on historical aerial photographs and our site observations, previous grading activities
and/or development have occurred on the property. As such, the contractor should
anticipate the presence of existing fill soils, pipe/culvert, active or abandoned utility lines,
and/or construction debris not encountered in the borings performed for this exploration.
If fill soils are encountered at other locations in the field during construction, the fill soils
should be observed by the Geotechnical Engineer-of-Record, or their authorized
representative, with respect to the criteria outlined in Section 5.0 – Construction
Considerations.
3.2.3. Residual Soils
Residual (undisturbed) soils were encountered below the surface materials and/or existing
fill soils in Borings B-4 and BMP-1, and extended to either the maximum termination depth
or partially weathered rock (PWR). These residual soils generally consisted of firm lean
clays (CL), stiff elastic silts (MH), firm to stiff sandy silts (ML), and very dense silty sands
(SM). The Standard Penetration Resistances (SPT N-values) in the residual soils ranged
from 5 to 55 bpf.
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3.2.4. Partially Weathered Rock and Auger Refusal
Partially weathered rock (PWR) conditions were encountered in Borings B-1, B-2, B-4, B-
5 and B-6 at approximate depths ranging from 5.5 to 17 feet below the existing ground
surface. PWR is defined as soil-like material exhibiting SPT N-values in excess of 100
bpf. When sampled, the PWR generally breaks down into sandy silts, silty sands and rock
fragments.
Auger refusal conditions were encountered in Borings B-1 through B-6 at approximate
depths ranging from 7.3 to 22.4 feet below the existing ground surface. Please note that
auger refusal was encountered in Boring B-3 on unknown material (possible building
debris). Auger refusal is defined as material that could not be penetrated by the drilling
equipment used during our field exploration. Materials that might result in auger refusal
include large boulders, rock ledges, lenses, seams or the top of parent bedrock. Core
drilling techniques would be required to evaluate the character and continuity of the refusal
material. However, rock coring was beyond the scope of this exploration and not
performed.
The following table summarizes the approximate depths that PWR and auger refusal
conditions were encountered in the borings performed for this exploration.
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Summary Table of Partially Weathered Rock and Auger Refusal Depths
Boring No. Partially Weathered Rock Approx. Depth, (feet)1 Auger Refusal Approx. Depth, (feet)1
B-1 9 9.3
B-2 17 22.4
B-3 --- 13*
B-4 5.5 7.3
B-5 8.5 9.3
B-6 8 10.5
BMP-1 --- ---
1Depths were measured from the existing ground surface at the time drilling was performed.
“---“ When PWR or auger refusal conditions were not encountered in the borings.
*Auger Refusal encountered on unknown material.
3.2.5. Groundwater Level Measurements
At the time of drilling, groundwater levels were observed in Borings B-3, B-4 and B-6 at
approximate depths of 10.2, 7.3 and 6.8 feet below the existing ground surface,
respectively. After waiting more than 24 hours, water levels were observed in Borings B-
3 and B-4 at approximate depths of 10.2 and 4.2 feet, respectively. Please note moisture
conditions of the soil samples were noted within some of the borings and moisture
conditions within the soils may be an indication of the presence of groundwater. Also,
moist to wet soil conditions can be an indication that some manipulation (scarifying and
drying) of the soil may be required in order to obtain the specified compaction during
grading operations.
It should also be noted that groundwater levels tend to fluctuate with seasonal and climatic
variations, as well as with some types of construction operations. Therefore, water may be
encountered during construction at depths not indicated in the borings performed for this
exploration.
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4.0 PRELIMINARY RECOMMENDATIONS
4.1. General
Our preliminary evaluation and recommendations are based on the project information outlined
previously and on the data obtained from the field and laboratory testing program. If the structural
loading, geometry, or proposed building locations are changed or significantly differ from those
outlined, or if conditions are encountered during construction that differ from those encountered
by the borings, SUMMIT requests the opportunity to review our recommendations based on the
new information and make necessary changes.
Grading plan information with proposed foundation bearing elevations was not available for our
review at the time of this report. Finish grade elevations of proposed construction in conjunction
with the proposed foundation bearing elevation can have a significant effect on design and
construction considerations. SUMMIT should be provided the opportunity to review the project
grading plans prior to their finalization with respect to the recommendations contained in this
report.
4.2. Foundation Recommendations
Based on the results of our borings and the assumed building loads, the proposed structure cannot
be adequately supported on shallow foundations systems bearing directly on the existing soil
conditions and construction debris without exceeding an acceptable amount of differential
settlements of the foundations due to the consolidation of the underlying soils. SUMMIT is
providing options for support of the proposed building foundation system which consist of 1)
shallow foundation system bearing on new structural fill, or 2) a deep foundation system such as
Drilled Shafts (“piers or caissons”) or Rammed Aggregate Piers. The third option could be
supporting the proposed structure on a Post Tension (PT) slab system.
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4.2.1. Shallow Foundation System bearing on New Structural fill
The proposed structure can be adequately supported on shallow foundation systems bearing on
new compacted structural fill soils provided the site preparation and compacted fill
recommendation procedures outlined in this report are implemented concerning unsuitable soils
such as poorly compacted existing fill soils, construction debris, organic laden and/or stained soils,
and soils with N-values less than 6 bpf. The existing fill soils and construction debris materials
should be undercut and replaced compacted structural fill material as outlined in Section 5 of this
report. An allowable net bearing pressure of up to 2,500 pounds per square foot (psf) can be used
for design of the foundations bearing on approved undisturbed residual soils, or on approved
structural fill compacted to at least 95 percent of its Standard Proctor maximum dry density. (Note:
the grading contractor can anticipate dewatering will be needed during the grading and
undercutting operations).
Provided the procedures and recommendations outlined in this report are implemented and using
loading information provided by the client, total and differential settlements were estimated to be
less than 1 inch and 0.5 inches, respectively.
To avoid punching type bearing capacity failure, we recommend wall foundation widths of 18
inches or more. Exterior foundations and foundations in unheated areas should be designed to
bear at least 12 inches below finished grade for frost protection. To reduce the effects of seasonal
moisture variations in the soils, for frost protection and for bearing capacity, it is recommended
that all foundations be embedded at least 12 inches below the lowest adjacent grade.
All footing excavations and undercutting remediation operations should be inspected by the
Geotechnical Engineer-of-Record or his qualified representative to confirm that suitable soils are
present at and below the proposed bearing elevation and that the backfill operations are completed
with the recommendations of this report. This inspection may include hand-auger and DCP testing.
If evaluation with DCP testing encounters lower penetration resistances than anticipated or
unsuitable materials are observed beneath the footing excavations, these bearing soils should be
corrected per the Geotechnical Engineer-of-Record’s recommendations.
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4.2.2. Shallow Foundation System bearing on Deep Foundation System
Based on our experience, a structural pad requiring undercutting of unsuitable soils and
replacement with structural fills to depths of eight (8) feet or greater, it is typically more
economical to support the structure on a deep foundation system. Therefore, due to the depths of
soft existing fill and debris encountered in borings, and possible existing pipe/culvert that crosses
the site, we recommend the proposed construction be supported on a deep foundation system such
as Drilled Shafts (“piers or caissons”) or Rammed Aggregate Piers could be used to support the
proposed building structure, or the proposed building structure could be supported on Post Tension
(PT) slab system. Also, due to the variable soils conditions and construction debris encountered
in the borings during this exploration, we recommend the existing subsurface conditions be further
explored with, but not limited to, additional borings and test pits.
Drilled Shaft Foundations Discussions
The proposed structure can be supported on Drill Shaft Foundations (also referred to as “caissons”
or “drilled piers”). If drilled shafts are selected, we recommend that the drilled shafts be designed
to bear on partially weathered rock (PWR). An allowable net bearing pressure of up to 10,000
pounds per square foot (psf) can be used for design of the foundations bearing on approved
undisturbed PWR. Also, should construction debris be encountered during construction (i.e.,
Boring B-3), the contractor may want to anticipate installing permanent steel casing to keep the
grout from seeping into the construction debris material.
Due to the variable density material and construction debris, the skin friction should be ignored.
Drilled shafts should be constructed as straight shafts through the existing fill soils, debris and
residual soils into the PWR. Straight shafts will be required so that drilled shafts can be cased
during construction and to allow for safe working conditions and provide quality installation.
Based on the loading conditions anticipated, belling will likely not be required. If belling of the
drilled shafts is necessary, hand excavation will be required in the PWR. The results of the borings
indicate that the groundwater level will be above the bottom of the drilled shafts. Groundwater
seepage into the drilled shaft can be controlled by advancing the casing into the PWR to seal the
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base of the drilled shaft and reduce the influx of groundwater. All drilled shafts should be hand
cleaned and dewatered prior to placement of concrete.
Due to the anticipated depth of the drilled shafts and shallow groundwater levels, temporary steel
casings could be used to install the drilled shafts. The drilling augers should have cutting teeth
that result in an excavation with little or no soil “cake”: on the sides. The shaft diameter should
be at least equal to the design diameter for the full depth. Extra care should be taken during
removal of the casings to limit disturbances to the nearby structures.
As previously indicated, Partially Weathered Rock (PWR) was encountered in Borings B-1, B-2,
B-4, B-5 and B-6 at depths ranging 5.5 to 17 feet. Since the drilled shafts are expected to advance
through weathered zones of rock, adequate construction equipment should be provided so that
deeper penetration can be achieved by drilling techniques, reducing hand excavation. In this
regard, the drilled shaft contractor should anticipate that carbide-tipped rock auger will be required
to advance the drilled shafts once earth auger refusal is obtained. Depending on the design depths
of the shafts, rock coring or other means of rock removal may be required.
After the proposed bearing level is reached and the bearing surface cleaned, conditions should be
observed by the geotechnical engineer to conform that the conditions encountered during
construction are similar to those upon which the design recommendations are based. The shaft
diameter, depth, plumbness and type of bearing material should be documented. Significant
deviation from the specified or anticipated soil conditions should be reported to the owner’s
representative and the foundation designer. On approval of the drilled shaft excavation, concreting
operations should begin as soon as practical, as delays could cause the need for additional cleaning
and groundwater seepage.
We recommend a 6 to 8-inch concrete slump. A head of at least five of concrete should be
maintained above the bottom of the casing during withdrawal to reduce the potential of concrete
“hanging up” inside the casing, which can cause soil intrusion below the casing. The concreting
of each drilled shaft should be continuous. During placement of concrete, care should be taken
not to bounce concrete off the casing sides or reinforcing steel, which can result in concrete
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segregation. The concrete should be placed down the center of the hole.
Rammed Aggregate Piers Discussions:
The proposed structure can be supported on Rammed Aggregate Piers. We recommend utilizing
the “Impact Pier” (IP) installation or vibroflot methods due to the presence of shallow groundwater
encountered in some of the boring. Please note that should construction debris be encountered
during construction (i.e., Boring B-3), the contractor may need to remove the construction debris
and replace with compacted fill material.
We recommend contacting a rammed aggregate pier contractor regarding the suitability of rammed
impact piers at the project site. The contractor can provide a design maximum allowable bearing
capacity depending on location and building loads. Also, the contractor can provide specific
recommendations based on total (unfactored) load data for individual column locations, once
available.
If filling needed to reach finished floor elevation (FFE), we recommend that the new fill be allowed
to “settle out” prior to the placement of the building superstructure. The contractor can coordinate
placement of the IP or vibroflot elements in consideration of the new fill to minimize impacts to
construction schedule.
We recommend that the IP or vibroflot installation QC program be monitored full time by the
Owner’s geotechnical consultant. The QC program includes conducting verification of crowd
stabilization, measurement of drill depths and aggregate lift thickness. These items should be
documented for each IP element installed to provide a complete record of foundation quality.
The IP or vibroflot design should be reviewed by the Geotechnical Engineer of Record and the
installation should be monitored full time by the Owner’s geotechnical consultant.
If filling needed to reach finished floor elevation (FFE), we recommend that the new fill be allowed
to “settle out” prior to the placement of the building superstructure. The consultant can coordinate
placement of the IP or vibroflot elements in consideration of the new fill to minimize impacts to
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
14
construction schedule.
4.2.3. Post Tension Slab System Discussions:
The proposed construction could be supported on a Post Tension Slab System provided the
structure does not exceed acceptable limits of total and differential settlement of the foundation
due to the consolidation of the underlying soils under the building loads. Once the building loads
have been established, and additional explorations (i.e., additional borings and test pits) have been
performed, and if needed, laboratory test (i.e., consolidation testing) have been performed, we can
perform settlement analysis to estimate the total and differential settlements.
Note: All footing excavations and undercutting remediation operations should be observed by the
Geotechnical Engineer-of-Record or their qualified representative to confirm that suitable soils are
present at and below the proposed bearing elevation and that the backfill operations are completed
with the recommendations of this report. This observation may include hand-auger and DCP
testing. If DCP testing encounters lower penetration resistances than anticipated or unsuitable
materials are observed beneath the footing excavations, these bearing soils should be corrected per
the Geotechnical Engineer-of-Record’s recommendations.
4.3. Seismic Site Class
SUMMIT has determined the Seismic Site Classification for this project site in accordance with
Chapter 16, Section 1613.5.2 of the 2012 North Carolina Building Code, Site Class Definitions
using Soil Shear Wave Velocity. We recommend this project be designed using a Seismic Site
Class of “C” (Very Dense Soil and Soft Rock) having an average shear wave velocity of 2,765
ft/sec and soil greater than 10 feet between the rock surface and project bottom of the spread
footing or matt foundation as defined in Table 1613.5.4 Site Class Definitions. The approximate
location of the ReMi Profile run was performed as shown on the Boring Location Plan (Figure 2)
included in Appendix 1 of this report. The results of the ReMi test are presented in graphical form
in Appendix 3 – ReMi Shear Wave Testing Results.
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
15
4.4. Low to Moderate Plasticity Moisture Sensitive Soils (CL and MH)
Low to moderate plasticity and moisture sensitive (lean clays and elastic silts) soils were
encountered in Borings B-1, B-2 and BMP-1 performed for this exploration. These fine-grained
soils are susceptible to moisture intrusion and can become soft when exposed to weather and/or
water infiltration. Consequently, some undercutting and/or reworking (drying) of the near-surface
soils may be required depending upon the site management practices and weather conditions
present during construction.
Should these materials be left in-place, special consideration should be given to providing positive
drainage away from the structure and discharging roof drains a minimum of 5 feet from the
foundations to reduce infiltration of surface water to the subgrade materials.
Note: Since Low to Moderate Plasticity and Moisture Sensitive Soils can become remolded (i.e.,
softened) under the weight of repeated construction traffic and changes in moisture conditions,
these soils should be evaluated and closely monitored by the Geotechnical Engineer-of-Record or
their qualified representative prior to and during fill placement. Additional testing and inspections
of moisture sensitive soils may be warranted such as laboratory testing, field density (compaction)
testing, hand auger borings with dynamic cone penetrometer (DCP) testing and/or test pit
excavations.
4.5. Wet Weather Conditions
Contractors should be made aware of the moisture sensitivity of the near soils and potential
compaction difficulties. If construction is undertaken during wet weather conditions, the surficial
soils may become saturated, soft, and unworkable. The contractor can anticipate reworking and/or
recompacting soils may be needed when excessive moisture conditions occur. Additionally,
subgrade stabilization techniques, such as chemical (lime or lime-fly ash) treatment, may be
needed to provide a more weather-resistant working surface during construction. Therefore, we
recommend that consideration be given to construction during the dryer months.
Surface runoff should be drained away from excavations and not allowed to pond. Concrete for
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
16
foundations should be placed as soon as practical after the excavation is made. That is, the exposed
foundation soils should not be allowed to become excessively dry or wet before placement of
concrete. Bearing soils exposed to moisture variations may become highly disturbed resulting in
the need for undercutting prior to placement of concrete. If excavations must remain open
overnight, or if rainfall becomes imminent while the bearing soils are exposed, we recommend
that a 2- to 4-inch-thick “mud-mat” of lean (2000 psi) concrete be placed on the bearing soils
before work stops for the night.
SUMMIT recommends that special care be given to providing adequate drainage away from the
building areas to reduce infiltration of surface water to the base course and subgrade materials. If
these materials are allowed to become saturated during the life of the slab section, a strength
reduction of the materials may result causing a reduced life of the section.
4.6. Floor Slabs
Constructing the slab-on-grade floor systems on the existing soil conditions is an option, however,
the owner is accepting the risk of additional total and differential settlements due to the
consolidation of variable existing soil conditions and debris under the proposed structure loads. If
the owner is willing to accept the risk, the contractor should follow the recommendations as
described in Section 5.2.
If the owner is not willing to accept the risk, we recommend the project structural engineer design
the slab-on-grade floor systems to be supported on 1) new structural fill from a complete undercut
and repair of unsuitable materials, 2) a deep foundation system, or 3) a post tension (PT) slab
system. Please note that the PT option is dependent on the results of additional explorations and
settlement analyses.
4.7. Pavements Subgrade Preparation
The pavement sections can be adequately supported on approved non-high plasticity residual soils,
or newly compacted fill, provided the site preparation and fill placement procedures outlined in
this report are implemented. Immediately prior to constructing the pavement section, we
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
17
recommend that the areas be proofrolled to detect any softened, loosened or disturbed areas that
may have been exposed to wet weather or construction traffic. Areas that are found to be disturbed
or indicate instability during the proofrolling should be undercut and replaced with adequately
compacted structural fill or repaired as recommended by the Geotechnical Engineer. This
proofrolling should be observed by the staff professional or a senior soils technician under his/her
direction. Proofrolling procedures are outlined in the “Site Preparation” section of this report.
Due to prevalence of near surface low to moderate plasticity elastic silts, remediation of pavement
subgrade soils may be recommended (as determined by the Geotechnical Engineer during
construction) including undercutting and replacement with additional NCDOT ABC
stone. Alternatively, lime stabilization of pavement subgrade may be a more economical option
and SUMMIT can provide lime stabilization mix design services if requested. This may be more
pronounced depending on the time of the year and seasonal conditions at the time of pavement
construction. We recommend contingency for some remediation efforts for the subgrade soils be
considered during the planning stage.
4.8. Cut and Fill Slopes
Permanent project slopes should be designed with geometry of 3 horizontal to 1 vertical or flatter.
The tops and bases of all slopes should be located 10 feet or more from structural limits and 5 feet
or more from parking limits. Fill slopes should be properly compacted according to the
recommendations provided in this report. In addition, fill slopes should be overbuilt and cut to
finished grade during construction to achieve proper compaction on the slope face. All slopes
should be seeded and maintained after construction and adhere to local, state and federal municipal
standards, if applicable.
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
18
5.0 CONSTRUCTION CONSIDERATIONS
5.1. Abandoned Utilities/Structures
SUMMIT recommends that any existing utility lines and foundations be removed from within
proposed building and pavement areas. The utility backfill and foundation material should be
removed and the subgrade in the excavations should be evaluated by a geotechnical professional
prior to fill placement. The subgrade evaluation should consist of visual observations, probing
with a steel rod and/or performing hand auger borings with Dynamic Cone Penetrometer tests to
evaluate their suitability of receiving structural fill. Once the excavations are evaluated and
approved, they should be backfilled with adequately compacted structural fill. Excavation backfill
under proposed new foundations should consist of properly compacted structural fill, crushed
stone, flowable fill or lean concrete as approved by the Geotechnical Engineer-of-Record.
5.2. Site Preparation
We recommend prior to fill placement the surface materials should be stripped/removed from the
proposed construction limits. Stripping and clearing should extend 10 feet or more beyond the
planned construction limits. Upon completion of the stripping operations, we recommend areas
planned for support of foundations, floor slabs, parking areas and structural fill be proof-rolled
with a loaded dump truck or similar pneumatic tired vehicle (minimum loaded weight of 20 tons)
under the observations of a staff professional. After excavation of the site has been completed, the
exposed subgrade in cut areas should also be proof-rolled. The proof-rolling procedures should
consist of four complete passes of the exposed areas, with two of the passes being in a direction
perpendicular to the proceeding ones. Any areas which deflect, rut or pump excessively during
proof-rolling or fail to “tighten up” after successive passes should be undercut to suitable soils and
replaced with compacted fill.
Depending on the proposed building foundation supporting method, the extent of any undercut
required should be determined in the field by an experienced staff professional or engineer while
monitoring construction activity. After the proof-rolling operation has been completed and
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
19
approved, final site grading should proceed immediately. If construction progresses during wet
weather, the proof-rolling operation should be repeated after any inclement weather event with at
least one pass in each direction immediately prior to placing fill material or aggregate base course
stone. If unstable conditions are experienced during this operation, then undercutting or reworking
of the unstable soils may be required.
5.3. Difficult Excavation
Based on the results of our soil test borings and dependent on final grades, it appears that the
majority of general excavation for footings and utilities will be possible with conventional
excavating techniques. We anticipate that the residual soils can be excavated using pans, scrapers,
backhoes, and front end loaders. Depending on the location, excavations deeper than
approximately 5.5 to 17 feet may require specialized equipment and procedures.
Partially weathered rock (PWR) conditions were encountered in five (5) of the borings and auger
refusal conditions were encountered in six (6) of the borings performed for this exploration. The
depth and thickness of partially weathered rock, boulders, and rock lenses or seams can vary
dramatically in short distances and between the boring locations; therefore, soft/hard weathered
rock, boulders or bedrock may be encountered during construction at locations or depths, between
the boring locations, not encountered during this exploration.
The table below may be used as a quick reference for rippability of in-place materials.
Summary of Rippability Based on SPT N-Values
N-Values as Shown
on Boring Logs Description of N-Values Anticipated Rippability
60 < N-Value N-values less than 60 bpf These materials may generally be excavated with heavy-duty equipment such as a Caterpillar D-8 with a single-shank ripper
60 < N-Value < 50/3”
N-values more than 60 bpf,
but less than 50 blows per 3 inches of penetration
These materials are considered marginally
excavatable, even with heavy-duty equipment.
50/3” < N-Value N-values more than 50 blows per 3 inches of penetration
Blasting and/or removal with impact hammers is typically required to excavate these materials.
*This table is for general information only. Actual rippability is dependent upon many other factors as stated
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
20
Summary of Rippability Based on SPT N-Values
N-Values as Shown on Boring Logs Description of N-Values Anticipated Rippability
above.
Care should be exercised during excavations for footings on rock to reduce disturbance to the
foundation elevation. The bottom of each footing should be approximately level. When blasting
is utilized for foundation excavation in rock, charges should be held above design grades. Actual
grades for setting charges should be selected by the contractor and he should be responsible for
any damage caused by the blasting. All loose rock should be carefully cleaned from the bottom
of the excavation prior to pouring concrete. Footing excavations in which the rock subgrade has
been loosened due to blasting should be deepened to an acceptable bearing elevation.
In our professional opinion, a clear and appropriate definition of rock should be included in the
project specifications to reduce the potential for misunderstandings. A sample definition of rock
for excavation specifications is provided below:
Rock is defined as any material that cannot be dislodged by a Caterpillar D-8
tractor, or equivalent, equipped with a hydraulically operated power ripper (or by
a Cat 325 hydraulic backhoe, or equivalent) without the use of drilling and blasting.
Boulders or masses of rock exceeding ½ cubic yard in volume shall also be
considered rock excavation. This classification does not include materials such as
loose rock, concrete, or other materials that can be removed by means other than
drilling and blasting, but which for any reason, such as economic reasons, the
Contractor chooses to remove by drilling and blasting.
5.4. Temporary Dewatering
During this exploration, at the time of drilling, groundwater levels were observed in Borings B-3,
B-4 and B-6 at approximate depths of 10.2, 7.3 and 6.8 feet below the existing ground surface,
respectively. After waiting more than 24 hours, water levels were observed in Borings B-3 and B-
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
21
4 at approximate depths of 10.2 and 4.2 feet, respectively. Should groundwater be encountered
while performing excavations associated with the construction, the contractor should be prepared
to promptly remove/dewater the water from the general construction area. Pump(s) should remain
on standby to handle groundwater as necessary. Details concerning dewatering should be
discussed with the geotechnical engineer and agreed upon with the contractor prior to proceeding
with construction. Also, depending on the groundwater conditions, the contractor may need to
contact a professional that specializes in designing a groundwater control system.
The groundwater levels should be kept a minimum of five (5) feet below the bottom of the
proposed excavation elevation. Dewatering shall be performed until the construction is completed.
If water is encountered, pumping must be maintained continuously from sumps and/or well points
for any beneficial dewatering to be derived and a back-up pump should also be maintained on-site.
Discontinuous pumping will result in softening of the subgrade soils and additional undercutting
may be required. The contractor should also be prepared to implement additional dewatering
procedures in the event water levels rise to the point it impacts construction.
Positive site drainage shall be maintained away from all working areas at all times to prevent
ponding of water that could soften and disturb the subgrade materials. The contractor shall be
prepared to implement alternative dewatering techniques should the need arise. All subgrade
surfaces and fill surfaces should be adequately sloped to provide positive drainage as construction
progresses. Undercutting due to softening of subgrade soils as a result of improper temporary
dewatering will be the contractor’s responsibility.
Note: Depending on final grades and groundwater level conditions, permanent dewatering
system(s) may need to be installed and maintained during and after construction.
5.5. Temporary Excavation Stability
Localized areas of soft or unsuitable soils not detected by our borings, or in unexplored areas, may
be encountered once grading operations begin. Vertical cuts in these soils may be unstable and
may present a significant hazard because they can fail without warning. Therefore, temporary
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
22
construction slopes greater than 5 feet in height should not be steeper than two horizontal to one
vertical (2H:1V), and excavated material should not be placed within 10 feet of the crest of any
excavated slope. In addition, runoff water should be diverted away from the crest of the excavated
slopes to prevent erosion and sloughing.
Should excavations extend below final grades, shoring and bracing or flattening (laying back) of
the slopes may be required to obtain a safe working environment. Excavation should be sloped or
shored in accordance with local, state and federal regulations, including OSHA (29 CFR Part 1926)
excavation trench safety standards.
5.6. Structural Fill
Soil to be used as structural fill should be free of organic matter, roots or other deleterious
materials. Structural fill should have a plasticity index (PI) less than 25 and a liquid limit (LL)
less than 50 or as approved by the Geotechnical Engineer-of-Record. Compacted structural fill
should consist of materials classified as either CL, ML, SC, SM, SP, SW, GC, GM, GP, or GW
per ASTM D-2487 or as approved by the Geotechnical Engineer-of-Record. Off-site borrow soil
should also meet these same classification requirements. Non-organic, low-plasticity on-site soils
are expected to meet this criterion. However, successful reuse of the excavated, on-site soils as
compacted structural fill will depend on the moisture content of the soils encountered during
excavation. We anticipate that scarifying and drying of portions of the on-site soils will be required
before the recommended compaction can be achieved. Drying of these soils will likely result in
some delay.
All structural fill soils should be placed within the proposed structural pad and extending at least
5 feet beyond the perimeter of the pad and foundation limits. All structural fill soils should be
placed in thin (not greater than 8 inches) loose lifts and compacted to a minimum of 95 percent of
the soil's Standard Proctor maximum dry density (ASTM D 698) at/or near optimum moisture
content (±2 percent). The upper 2 feet of structural fill should be compacted to a minimum of 100
percent of the soil's Standard Proctor maximum dry density (ASTM D 698) at/or near optimum
moisture content (±2 percent). Some manipulation of the moisture content (such as wetting,
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
23
drying) may be required during the filling operation to obtain the required degree of compaction.
The manipulation of the moisture content is highly dependent on weather conditions and site
drainage conditions. Therefore, the grading contractor should be prepared to both dry and wet the
fill materials to obtain the specified compaction during grading. Sufficient density tests should be
performed to confirm the required compaction of the fill material.
5.7. Engineering Services During Construction
As previously stated, the engineering recommendations provided in this report are based on the
project information outlined above and the data obtained from field and laboratory tests. However,
unlike other engineering materials like steel and concrete, the extent and properties of geologic
materials (soil) vary significantly. Regardless of the thoroughness of a geotechnical engineering
exploration, there is always a possibility that conditions between borings will be different from
those at the boring locations, that conditions are not as anticipated by the designers, or that the
construction process has altered the subsurface conditions. This report does not reflect variations
that may occur between the boring locations. Therefore, conditions on the site may vary between
the discrete locations observed at the time of our subsurface exploration.
The nature and extent of variations between the borings may not become evident until construction
is underway. To account for this variability, professional observation, testing and monitoring of
subsurface conditions during construction should be provided as an extension of our engineering
services. These services will help in evaluating the Contractor's conformance with the plans and
specifications. Because of our unique position to understand the intent of the geotechnical
engineering recommendations, retaining us for these services will also allow us to provide
consistent service through the project construction. Geotechnical engineering construction
observations should be performed under the supervision of the Geotechnical Engineer-of-Record
from our office who is familiar with the intent of the recommendations presented herein. This
observation is recommended to evaluate whether the conditions anticipated in the design actually
exist or whether the recommendations presented herein should be modified where necessary.
Observation and testing of compacted structural fill and backfill should also be provided by our
firm.
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
24
6.0 RELIANCE AND QUALIFICATIONS OF REPORT
This geotechnical subsurface exploration has been provided for the sole use of Laurel Street
Residential. This geotechnical subsurface exploration should not be relied upon by other parties
without the express written consent of SUMMIT and Laurel Street Residential.
The analyses and recommendations submitted in this report were based, in part, on data obtained
from this exploration. If the above-described project conditions are incorrect or changed after the
issuing of this report, or subsurface conditions encountered during construction are different from
those reported, SUMMIT should be notified and these recommendations should be re-evaluated
based on the changed conditions to make appropriate revisions. We have prepared this report
according to generally accepted geotechnical engineering practices. No warranty, express or
implied, is made as to the professional advice included in this report.
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
APPENDIX 1 – Figures
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
APPENDIX 2 – Subsurface Diagram and Boring Logs
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
ABBREVIATIONS
TV
PID
UC
ppm
-
-
-
-
TORVANE
PHOTOIONIZATION DETECTOR
UNCONFINED COMPRESSION
PARTS PER MILLION
LIQUID LIMIT (%)
PLASTIC INDEX (%)
MOISTURE CONTENT (%)
DRY DENSITY (PCF)
NON PLASTIC
PERCENT PASSING NO. 200 SIEVE
POCKET PENETROMETER (TSF)
LL
PI
W
DD
NP
-200
PP
-
-
-
-
-
-
-
Standard Penetration Test
SAMPLER SYMBOLSLITHOLOGIC SYMBOLS
(Unified Soil Classification System)
CL: USCS Low Plasticity Clay
DEBRIS: Various Construction, Concrete
And Unknown Debris
FILL: Fill (made ground)
GP: USCS Poorly-graded Gravel
MH: USCS Elastic Silt
MLS: USCS Sandy Silt
SM: USCS Silty Sand
TOPSOIL: Topsoil
PWR: Partially Weathered Rock
WELL CONSTRUCTION SYMBOLS
KEY TO SYMBOLS
Water Level at Time
Drilling, or as Shown
Water Level After 24, or as Shown
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
670
672
674
676
678
680
682
684
686
688
690
692
694
696
670
672
674
676
678
680
682
684
686
688
690
692
694
696
678.3 ft.
9
21
3
50/3"
0.33
1
3
5.5
99.3
671.6 ft.
10
10
15
12
23
50/5"
50/0"
0.33
5.5
8
12
17
22.4
677 ft.
4
25
6
1
50/0"
0.33
3
5.5
8
13
684.2 ft.
36
55
50/3"
50/0"
0.33
1
3
5.5
7.3
681.7 ft.
22
9
16
50/4"
0.33
3
5.5
8.5
9.3
680 ft.
24
15
20
50/6"
50/0"
0.33
3
5.5
8
10.5
678 ft.
3
8
11
10
5
8
6
11
0.75
1
2
4
6
8
10
12
14
16
Topsoil Partially Weathered Rock
USCS Silty Sand Asphalt
USCS Elastic Silt USCS Low Plasticity Clay
Various Construction, Concrete And other DebrisUSCS Poorly-graded
Gravel
USCS Sandy SiltPROJECT NAME 7th Street Apartments
PROJECT LOCATION Charlotte, North Carolina
CLIENT Laurel Street Residential
PROJECT NUMBER 4164.11
Elevation (ft)SUBSURFACE DIAGRAMSUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
DepthN-Value
B-1687.5 ft.
DepthN-Value
B-2
694 ft.
DepthN-Value
B-3690 ft.
DepthN-Value
B-4
691.5 ft.
DepthN-Value
B-5691 ft.
DepthN-Value
B-6690.5 ft.
DepthN-Value
BMP-1
694 ft.
FILL with Construction Debris (Concrete Debris)
Sampled as Construction Debris (Concrete Debris) and Gravel
Sampled as Construction Debris (Asphalt Debris)
FILL with a trace of Construction Debris (Unknown Plastic Material)
FILL - Organic Stained
FILL - Organic Stained
FILL with Construction Debris (Brick Veneer)
Refusal on
Unknwon Material
SPT1
SPT
2
SPT3
SPT49ft
Approx. 4" of Topsoil
(ML) FILL:Moist Reddish Brown Slightly Clayey Sandy SILT
(ML) FILL:Stiff Moist Red Slightly Micaceous Slightly Clayey Sandy SILT
(SM) FILL:
Medium Dense Black Silty SAND with Rock Fragments
(MH) FILL:Soft Wet Red Elastic SILT
(ML) RESIDUUM:
Partially Weathered Rock (PWR) when sampled becomes GrayRock Fragments
Bottom of Boring at 9.3 feet bgs, Auger Refusal
4-5-4(9)
5-7-14
(21)
1-1-2(3)
9-50(50/3")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring Location
GROUND ELEVATION 687.5 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/7/19 COMPLETED
AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 9' bgs
AT END OF DRILLING ---
HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)687.5
682.5
677.5
672.5
667.5
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-1
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
SPT1
SPT
2
SPT3
SPT
4
SPT
5
SPT
6
SPT7
17.2ft
Approx. 4" of Topsoil
(MH) FILL:Stiff Brownish Red Elastic SILT
(SM) FILL:Medium Dense Light Brown Silty SAND with Rock Fragments
(ML)FILL:
Stiff Red Slightly Clayey Sandy SILT
(MH) FILL:
Very Stiff Light Brown and Gray Elastic SILT with Gray and WhiteSilty SAND
(ML)RESIDUUM:
Partially Weathered Rock (PWR) when sampledbecomes Olive Brown and Gray Slightly ClayeySandy SILT
Bottom of Boring at 22.4 feet bgs, Auger Refusal
4-4-6(10)
4-4-6
(10)
5-8-7(15)
5-6-6
(12)
4-8-15
(23)
13-27-50
(50/5")
50(50/0")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 694 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED
AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 17.2' bgs
AT END OF DRILLING ---
HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)694.0
689.0
684.0
679.0
674.0
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-2
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
>>
SPT1
SPT
2
SPT3
SPT
4
SPT5
10.2ft10.4ft
10.6ft
Approx. 4" of Topsoil
(ML) FILL:Soft Moist Reddish Brown Slightly Clayey Sandy SILT
(ML) FILL:
Very Stiff Moist Reddish Brown Slightly Clayey Sandy SILT withConstruction Debris (Concrete Debris)
(ML) FILL:Sampled as Construction Debris (Concrete Debris) and Gravel
(ML) FILL:
Sampled as Construction Debris (Asphalt Debris)
Bottom of Boring at 13 feet bgs, Auger Refusal on Unknown Material
3-2-2(4)
22-9-16
(25)
3-3-3(6)
0-0-1
(1)
50(50/0")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 690 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AT TIME OF DRILLING 10.4ft/ Elev 679.6ft GW ATD /Caved in@ 10.6'
AFTER 24 HRS DRILLING 10.20 ft / Elev 679.80 ft GW > 24 Hrs
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)690.0
685.0
680.0
675.0
670.0
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-3
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
SPT1
SPT
2
SPT3
SPT4
4.2ft4.5ft
7.3ft
Approx. 4" of Topsoil
(ML)FILL:Moist Reddish Brown Slightly Clayey Sandy SILT
(ML)FILL:Hard Red Slightly Clayey Sandy SILT
(SM) RESIDUUM:
Very Hard Yellowish Red and Red Slightly Clayey Silty SANDwith Rock Fragments
(SM) Partially Weathered Rock (PWR) when sampled becomesYellowish Red Silty SAND with Rock Fragments
Bottom of Boring at 7.3 feet bgs, Auger Refusal
10-18-18(36)
7-13-42
(55)
50(50/3")
50(50/0")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 691.5 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED
bgs
HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AT TIME OF DRILLING 7.3ft /Elev 684.2ft GW ATD /Caved in @4.5'
AFTER 24 HRS DRILLING 4.20 ft / Elev 687.30 ft GW > 24 Hrs
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)691.5
686.5
681.5
676.5
671.5
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-4
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
>>
SPT1
SPT
2
SPT3
SPT4
6.8ft
Approx. 4" of Topsoil
(ML) FILL:Very Stiff Black (Organic Stained) and Light Brown SlightlyClayey Sandy SILT
(ML) FILL:
Stiff Light Brown and Red Slightly Clayey Sandy SILT
(ML) FILL:Very Stiff Dark Olive Brown Slightly Micaceous Sandy SILT with a
trace of Construction Debris (Unknown Plastic Material)
(SM) RESIDUUM:Partially Weathered Rock (PWR) when sampled becomes Light
Brown Silty SAND with Rock Fragments
Bottom of Boring at 9.3 feet bgs, Auger Refusal
6-9-13(22)
6-4-5
(9)
6-5-11(16)
16-50(50/4")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 691 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 6.8'bgs
AFTER 24 HRS DRILLING --- GW > 24 Hrs NE
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)691.0
686.0
681.0
676.0
671.0
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-5
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
SPT1
SPT
2
SPT3
SPT4
SPT5
6.8ft
7ft
Approx. 4" of Topsoil
(ML)FILL:Very Stiff Brown and Red Slightly Clayey Sandy SILT with a traceof Gravel
(SM) FILL:
Medium Dense Red Silty SAND with Construction Debris (BrickVeneer)
(ML)FILL:Very Stiff Dark Brown (Organic Stained) Sandy SILT with Rock
Fragments
(SM) RESIDUUM:
Partially Weathered Rock (PWR) when sampled becomes Brownand White Silty SAND with Rock Fragments
Bottom of Boring at 10.5 feet bgs, Auger Refusal
4-7-17(24)
8-8-7
(15)
6-8-12(20)
9-50(50/6")
50(50/0")
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 690.5 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED
bgs
HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AT TIME OF DRILLING 6.8ft / Elev 683.7ft GW ATD /Caved in @ 7'
AT END OF DRILLING ---
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)690.5
685.5
680.5
675.5
670.5
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER B-6
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
>>
>>
SPT1
SPT2
SPT3
SPT4
SPT5
SPT6
SPT7
SPT8
11.6ft
Approx. 8" of Asphalt
(GP) Approx. 4" of Crush Aggregate Stone
(MH) FILL:Dark Reddish Brown and Red Sandy Elastic SILT
(MH) FILL:
Firm Moist Red and Reddish Yellow Slightly Sandy Elastic SILT
(MH) RESIDUUM:
Stiff Dark Red Slightly Sandy Elastic SILT
(MH) Stiff Red Slightly Sandy Elastic SILT
(CL) Firm Moist Red and Light Gray Slightly Sandy Lean CLAY
(CL) Firm Moist Yellowish Red, Yellow and Black Slightly Sandy
Lean CLAY
(ML) Firm Moist Reddish Yellow, Yellow and Light Gray Slightly
Clayey Slightly Sandy SILT
(ML) Stiff Moist Light Gray, Very Pale Brown and Black Slightly
Clayey Sandy SILT
Bottom of Boring at 16 feet bgs, Boring Terminated
0-0-3-4(3)
4-4-4-4(8)
3-5-6-6(11)
3-4-6-6(10)
2-2-3-4(5)
4-4-4-4(8)
2-2-4-9(6)
3-4-7-8(11)
NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring
GROUND ELEVATION 694 ft
LOGGED BY Angel
DRILLING METHOD Hollow Stem Auger
DRILLING CONTRACTOR FST
CHECKED BY T. Costner
DATE STARTED 11/6/19 COMPLETED
AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 11.6' bgs
AT END OF DRILLING --- GW > 24 Hrs NE
HOLE SIZE 6 inches
GROUND WATER/CAVE-IN:
AFTER DRILLING ---RECOVERY %(RQD)20 40 60 800 100
PL LLMC
FINES CONTENT (%)
20 40 60 800 100GRAPHICLOGELEVATION(ft.)694.0
689.0
684.0
679.0
674.0
5.0
10.0
15.0
20.0 SAMPLE TYPENUMBERMATERIAL DESCRIPTION
BLOWCOUNTS(N VALUE) SPT N VALUE
20 40 60 800 100
PAGE 1 OF 1
BORING NUMBER BMP-1
PROJECT NUMBER 4164.11 PROJECT LOCATION Charlotte, North Carolina
PROJECT NAME 7th Street ApartmentsCLIENTLaurel Street Residential
SUMMIT Enginnering, Laboratory and Testing PC
3575 Centre Circle Drive
Fort Mill, South Carolina 28273
704.504.1717
www.summit-companies.com
Report of Preliminary Geotechnical Subsurface Exploration SUMMIT Project No. Project 4164.11
7th Street Apartments December 10, 2019
APPENDIX 3 – ReMi Test Results
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Depth, ftShear-Wave Velocity, ft/s
Vs100' = 2765 ft/s
7th Street Apartments, Charlotte, NC:Vs Model
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
4500.00
0 0.05 0.1 0.15 0.2 0.25Rayleigh Wave Phase Velocity,ft/sPeriod, s
Dispersion Curve Showing Picks and Fit
Calculated Dispersion
Picked Dispersion
7th Street Apartments, Charlotte, NC
p-f Image with Dispersion Modeling Picks