Item No 18 - Report of Subsurface Exploration Morehead Commo-OCR

REPORT OF
SUBSURFACE EXPLORATION
MOREHEAD COMMON
BUILDINGS 1321 AND 23 AND
PROPOSED RETAINING WALL
CHARLOTTE NORTH CAROLINA
ESP PROJECT NO E4-UD42.302
Beazer Homes
1300 South Boulevard
Suite
Charlotte North Carolina 28203-4265
ESP Associates P.A
Box 7030
Charlotte North Carolina 28241
ESP Associates P.A
Prepared For
i1
Prepared By
July 2007
$ESP
ESP Associates P.A
July 2007
Beazer Homes
1300 South Boulevard
Suite
Charlotte North Carolina 28203-4265
Attention Mr Jade Eastridge
Reference REPORT OF SUBSURFACE EXPLORATION
Morehead Common
Buildings 1321 and 23 and Proposed Retaining Wall
Charlotte North Carolina
ESP Project No E4-UD42.302
Dear Mr Eastridge
ESP Associates P.A ESP has completed the subsurface exploration for Buildings 13 21 and
23 and proposed retaining wall for the proposed Morehead Common site in Charlotte North
Carolina This exploration was performed in general accordance with our Proposal No E4-
07035 dated February 16 2007 Authorization to proceed with this study was provided by
written execution of our proposal by Mr Jade Eastridge of Beazer Homes
The purpose of the exploration was to evaluate the general subsurface conditions within the
proposed building areas of Building Nos 13 21 and 23 and the proposed retaining wall to the
east of Dunbar Street with regard to the design and construction of the foundation systems This
report presents
our findings conclusions and recommendations for foundation design as well as
construction considerations for the proposed foundations areas ESP has also previously
P.O Box 7030 Charlotte NC 28241
1.800.960.7317 NC 704.583.4949 fax [phone] SC 803.802.2440 fax [phone]
www.espassociates.com
provided subsurface exploration services for portions of the Morehead Common site Please
refer to our reports titled Report of Preliminary Subsurface Exploration dated May 26 2006
Addendum to Report of Preliminary Subsurface Exploration dated August 18 2006
and
Addendum to Report of Preliminary Subsurface Exploration dated January 15 2007
respectively for details
ESP appreciates the opportunity to assist you during this phase of the project If you should have
any questions concerning
this report or if we may be of further assistance please
contact us
Sincerely
ESP Associates P.A
Report ofSubsurface Exploration
Morehead Common Buildings 13 21 and 23
ESP Project No E4-UD42 302
July 2007
Copies Submitted
cc Mr Kenny Hanes Gelder Thompson
Mr Kraig Klaussen Echelon Engineering
Mr Joe Herman The Preston Partnership
TABLE OF CONTENTS
1.0 INTRODUCTION
1.1 SITE AND PROJECT DESCRiPTION
1.2 PURPOSE OF SERVICES
2.0 EXPLORATION PROCEDURES
2.1 FiELD
2.2 LABORATORY
3.0 SUBSURFACE CONDITIONS
3.1 PFIYSIOGRAPHY AND AREA GEOLOGY
3.2 SUBSURFACE CONDITIONS
3.2.1 BUiLDiNG 13
3.2.2 BUILDING 21
3.2.3 BUILDING 23
3.2.4 RETAINING WALL
3.3 SUBSURFACE WATER
4.0 CONCLUSIONS AND RECOMMENDATIONS 10
4.1 GENERAL 10
4.2 SITE DEVELOPMENT 10
4.2.1 BUILDiNG 13 10
4.2.2 BUILDING 21 11
4.2.3 BUILDING 23 12
4.3 EXISTING FILL 13
4.4 PRELIMiNARY FOUNDATION SUPPORT 14
4.5 FLOOR SLABS 16
4.6 FOUNDATION WALLS 16
4.7 CUT AN FILL SLOPES 18
5.0 CONSTRUCTION CONSIDERATIONS 19
5.1 EXISTING UTILITIES 19
5.2 SITE PREPARATION 19
5.3 TEMPORARY EXCAVATION STABILITY 20
5.4 DIFFICULT EXCAVATION 21
5.4.1 BUILDING 13 21
5.4.2 BUILDING 21 22
5.4.3 BUILDING 23 23
5.4.4 RETAINING WALL 23
5.5 FILL MATERIAL AND PLACEMENT 24
5.6 TEMPORARY DEWATERING 25
5.7 SLOPING OF BUILDING PADS 25
6.0 LIMITATIONS OF REPORT 26
TABLE OF CONTENTS continued
APPENDIX
FIELD EXPLORATION PROCEDURES
LABORATORY PROCEDURES
BORING LOCATION PLAN FIGURE
STANDARD PROCTORS S-i S-5
GRAIN SIZE ANALYSIS S-i S-5
ATTERBERG LIMITS S-i S-5
TRIAXTAL TEST S-i S-4 S-5
CONSOLIDATION TEST S-2 S-3
LEGEND TO SOIL CLASSIFICATION
AND SYMBOLS
TEST BORING RECORDS B-13 THROUGH B-3
Report of Subsurface Exploration ESP Project No E4-UD42.302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
1.0 INTRODUCTION
1.1 SITE AND PROJECT DESCRIPTION
The proposed site consists of approximately 22.8 acres of land located in Charlotte North Carolina
reference Boring Location Plan Figure At the time of our exploration the site consisted
of 10 generally vacant grass or gravel-covered lots The area is bounded on the north by
Morehead Street to the south by Post Street to the east by the intersection of Morehead
Street and 1-277 and to the west by the existing but partially demolished Duke Power building
and newer/remoldeled commercial office building More specifically the lots are listed as Tax
Parcel 073-252-11 073-252-10 073-252-09 073-256-01 073-256-02 073-141-05 portion of
Parcel 073-252-13 073-252-07
073-255-01 and 073-142-01 Two single-story block buildings
were observed in the northern quadrant of the intersection
of Clatkson and Dunbar Streets
Relief on the site is estimated to be on the order of 46 feet with the site generally sloping
downward from southeast to northwest Several existing roadways are present throughout the
site These roadways iLikely have existing utility infrastructure associated with them storm
water utility line was observed traversing Tax Parcel 073-255-0 from south to north through
the parcel In general significant site grading appears to have taken place throughout the site in
the past ESP has previously performed several subsurface explorations on the referenced site
Please refer to ESPs previous reports titled Report of Preliminary Subsurface Exploration
dated May 26 2006
Addendum to Report of Preliminary Subsurface Exploration dated
August 18 2006
and Addendum to Report of Preliminary Subsurface Exploration dated
January 15 2007
We understand that plans are to construct residential development consisting of multi-family
dwellings with associated roadways and infrastructure on the referenced property We
understand that the three proposed five-story mid-rise structures Buildings 13 21 and 23
considered in this analysis have been preliminarily designed for shallow foundations and first
Report ofSubs urface Exploration ESP Project No E4-UD42.302
Morehead Common Buildings /3 21 and 23 and Proposed Retaining Wall July 2007
floor level post-tensioned slabs with elevated wood-framed floor systems Also double-tier
geogrid-reinforced modular block retaining wall is planned for the eastern side of the site The
wall will support cut face to the east and south and will provide the grade change from the
adjacent property to SDunbar Street Structural loading information for the buildings was
provided via e-mails dated February and March 19 2007
from Mr Malcolm Foss with
Echelon Engineering with an attached mid-rise first level floor plan Maximum column and
wall loads are on the order of 280 kips and 15 kips per foot respectively At the time our
services finished floor elevations FFE for Building Nos 13 21 and 23 of 691.33 669.33 and
660.0 feet respectively were provided by Tumbull Sigmon Design No other detailed
information has been provided at this time
1.2 PURPOSE OF SERVICES
The purpose of the exploration was to evaluate the general subsurface conditions within
Buildings 12 21 23 and the retaining walls with regard to the design and construction of the
foundation systems It should be noted that the scope of this exploration was increased on April
16 2007 to include additional settlement analyses for proposed Buildings 13 21 and 23 This
additional work was authorized by Mr Jade Eastridge with Beazer Homes This report presents
our findings conclusions and recommendations for foundation design as well as construction
considerations for the proposed foundations areas This report also contains brief description
of the field testing procedures performed
for this study and discussion of the soil conditions
encountered at the site
2.0 EXPLORATION PROCEDURES
2.1 FIELD
During preparation
of our exploration plan ESP reviewed the test results from within our
previous report titled Report of Preliminary Subsurface Exploration dated May 26 2006 For
this analysis nineteen 19 additional soil test borings Borings B-13 through B-3 were
Report of Subsurface Exploration ESP Project No E4-UD42.302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
performed by ESP at the approximate locations shown on the attached Boring Location Plan
Figure The building and retaining wall locations were staked in the field by ESP using the site
plan provided by Tumbull Sigmon Design titled Site Plan dated November 20 2006 The
boring locations were selected by ESP and were field-located using the staked building corners
and wall locations as references for measuring distances and approximating right angles The
sOil test borings were extended to depths ranging
between approximately 15 and 33.5 feet below
the existing ground surface using an ATV-mounted CME 550X drill rig Hollow-stem
continuous flight augers were used to advance the borings into the ground
Standard Penetration Tests were performed at designated intervals in the soil test borings in
general accordance with ASTM 1586 in order to obtain data for estimating soil strength and
consistency In conjunction with the penetration testing split-spoon soil samples were recovered
for soil classification arid potential laboratory testing Water level measurements were attempted
at the termination of drilling and day after the termination of drilling brief description of
the field testing procedures is included in the Appendix
While in the field representative of the geotechnical engineer visually examined each boring
sample to evaluate the type of soil encountered soil plasticity moisture condition organic
content presence of lenses and seams colors and apparent geological origin The results of the
visual soil classifications for the borings as well as field test results are presented on the
individual Test Boring Records included in the Appendix Similar soils were grouped into
strata on the boring records The strata lines represent approximate boundaries between the soil
types however the actual transition between soil types in the field may be gradual in both the
horizontal and vertical directions
2.2 LABORATORY
Select samples of the on-site soils obtained during the field testing program were tested in the
laboratory Tests performed on select samples included Atterberg limits sieve analyses Standard
Report of Subsurface Exploration ESP Project No E4-UD42 302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
Proctor moisture-density relationships triaxia shear tests and consolidation tests The limited
testing program was designed to determine selected engineering properties of the on-site soils
relative to their use for the project The results of the soil tests performed for this study along
with
brief description of the laboratory procedures used are presented in the Appendix brief
summary of results is provided below
TABLE 1-SUMMARY OF LABORATORY TESTING
ESP Sample Liquid Percent Standard Proctor Consolidation Triaxial Shear Results
Sample Description Limit Passing Moisture-Density Test Results
No Plasticity No 200 Maximum Optimum Effective Effective
Location Index Sieve Dry Density Moisture
pci Content degrees psi
Brown Sandy Lean
S-i CLAY Bulk 44/24 65.6 108.5 18.0 27 180
B-19A2to5ft
Brown Clayey Silty
S-2 SAND undisturbed ---See Appendix
B-19Al5toi7ft
Brown and Tan and
Orange Fine Sandy
SILT undisturbed ee Appenuix
B-30Ai0tol2fi
Orange and Tan Silty
S-4 SAND undisturbed 33
B-18AlOtol2ft
Tan and White Sandy
S-5 SILTBuIk 34/8 59.5 117.5 14.5 30
B-13 toB-i8 2to7ft
3.0 SUBSURFACE CONDITIONS
3.1 PHYSIOGRAPHY AND AREA GEOLOGY
The referenced property is located in Charlotte North Carolina which is in the Piedmont
Physiographic Province The Piedmont Province generally consists of hills and ridges that are
intertwined with an established system of draws and streams The Piedmont Province is
predominately underlain by igneous rock formed from molten material and metamorphic rock
formed by
heat pressure andlor chemical action which were initially formed during the
Precambrian and Paleozoic eras
Report of Subsurface Exploration ESP Project No E4-UD42 302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
The virgin soils encountered in this area are the residual product of inp1ace chemical weathering
of rock In areas not altered by erosion or disturbed by the activities of man the typical residual
soil profile consists of clayey soils near the surface where soil weathering is more advanced
underlain by sandy silts and silty sands The boundary between soil and rock is not sharply
defined This transitional zone termed partially weathered rock is normally found overlying
the parent bedrock Partially weathered rock is defined for engineering purposes as residual
material with Standard Penetration Resistances in excess of 100 blows per foot Weathering is
facilitated by fractures joints and by the presence of less resistant rock types Consequently
the
profile of the partially weathered rock and hard rock is quite irregular and erratic even over short
horizontal distances Also it is common to find lenses and boulders of hard rock and zones of
partially weathered rock within the soil mantle well above the general bedrock level
3.2 SUBSURFACE CONDITIONS
Subsurface conditions as indicated by the borings generally consist of gravel underlain by fill or
residual soils The residual soils have formed from the weathering of the parent bedrock The
generalized subsurface conditions at the site are described below For more detailed soil
descriptions and stratifications at particular boring location the respective Test Boring
Record should be reviewed The Test Boring Records are included in the Appendix
3.2.1 BUILDING 13
Surface gravel layer approximately inches thick was initially encountered in all of the
borings performed
on Building Pad 13 Borings B-13 through B-18
Fill An auger probe
was initially performed on Borings B-l3 through B-18 due to the
significant amount of cut to achieve proposed FFE Fill soils were encountered underlying the
surface materials in Boring B-i The fill consists of firm sandy silts and clayey silts Standard
Report of Subsurface Exploration ESP Project No E4-UD42.302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
Penetration Resistances N-values in the fill were blows per foot bpf The fill extends to
depth of approximately 9.5 feet below the existing ground surface
Residuum From the proposed FFE in Borings B-13 and B-15 through B-17 and beneath the fill
soils in Boring B-18 residual soils were encountered The residuum generally consists of stiff
clayey silts and sandy silts and loose to very dense silty sands N-values in the residuum varied
widely between and 68 bpf Borings B-13 and B-15 were terminated in the residuum at depths
of approximately 33.5 and 30 feet respectively below the existing ground surface Boring B-16
resulted in auger refusal within the residuum at depth of 21.1 feet below the existing ground
surface Auger refusal is defined as material that could not be penetrated with the drill rig
equipment used on this project Auger refusal may consist of 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
Partially Weathered Rock Underlying the residuum in Borings B-14 and B-17 and B-18
partially weathered rock PWR was encountered PWR is defined as residual soils exhibiting
N-values in excess of 100 bpf When sampled the PWR generally breaks down into sandy silts
and silty sands with rock fragments Borings B-17 and B-18 were terminated in the PWR at
depths of 30 and 27 feet respectively Boring B-14 was terminated in the PWR upon auger
refusal at depth of 15 feet Auger refusal is defined as material that could not be penetrated
with the drill rig equipment used on this project Auger refusal may consist of 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
3.2.2 BUILDING 21
Surface gravel layer approximately to 18 inches thick was initially encountered in all of
the borings performed on Building Pad 21 Borings B-19 through B-24
Report ofSubsurface ploration ESP Project No E4-UD42.302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
Fill Fill soils were encountered underlying the surface material in Borings B-19 through B-22
and B-24 The fill consists of soft to stiff silty clays sandy clays sandy silts clayey silts and
medium dense silty sands High plasticity clays were encountered in Boring B-2l from to 5.5
feet below the existing elevation N-values in the fill ranged from to 15 bpf The fill extends
to depths ranging
between and 14 feet below the existing ground surface
Residuum Underlying the surface materials in Boring B-23 and beneath the fill in all of the
remaining borings performed
on Building Pad 21 residual soils were encountered The
residuum generally consists of firm to very stiff silty clays sandy clays sandy silts clayey silts
and loose to very dense silty sands N-values in the residuum varied widely between and
90 bpf Borings B-19 B-20 and B-22 through B-24 were terminated in the residuum at depth
of approximately 25 feet below the existing ground surface
Partially Weathered Rock Beneath the residuum in Boring B-21 partially weathered rock
PWR was encountered PWR is defined as residual soils exhibiting N-values in excess of 100
bpf When sampled the PWR generally breaks down into sandy silts and silty sands with rock
fragments Boring
B-21 was terminated in the PWR upon auger refusal at depth of
approximately 18.8 feet Auger refusal is defined as material that could not be penetrated with
the drill rig equipment used on the project Auger refusal material may consist of 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
3.2.3 BUILDING 23
Surface gravel layer approximately to inches thick was initially encountered in all of the
borings performed on Building Pad 23 Borings B-25 through B-30
Fill Fill soils were encountered underlying the surface material in Borings B-25 through B-30
The fill consists of firm to stiff silty clays clayey sandy silt and sandy silts The fill material
Report of Subsurface Exploration ESP Project No E4-UD42.302
Morehead Common Buildings 13 21 and 23 and FroposedRetaining Wall July 2007
encountered in Boring B-26 consisted of concrete fragments to depths of 5.5 feet below the
existing elevation N-values in the fill ranged from to 12 bpf The fill extends to depths
ranging between and feet below the existing ground surface
Residuum Underlying the fill material in Borings B-25 through B-30 residual soils were
encountered The residuum generally consists of firm to stiff sandy silts and clayey silts and
loose to dense silty sands N-values in the residuum varied widely between and 43 bpf
Borings B-25 through B-30 were terminated in the residuum at depth of approximately 25 feet
below the existing ground surface
3.2.4 RETAINING WALL
Surface gravel/grass layer approximately inches thick was initially encountered in Boring
B-3 performed in the proposed retaining wall area
Partially Weathered Rock An auger probe
was performed to depth of approximately 18 feet
approximate bottom of wall elevation below the existing elevation where PWR was
encountered PWR is defined as residual soils exhibiting N-values in excess of 100 bpf When
sampled the PWR generally breaks down into sandy silts and silty sands with rock fragments
Boring B-3 was terminated in the PWR at depth of approximately 27 feet
3.3 SUBSURFACE WATER
Water level measurements were attempted in the borings at the termination of drilling and day
after the termination of drilling At termination water was observed in Borings B-l9 B-20
21 and B-27 at depths of 20 21.5 16.8 and 20.7 feet respectively below the existing ground
surface The remainder of the borings were dry at termination Subsequent water levels
measured at day indicated water was present in Borings B-19 through B-23 B-25 through B-27
and B-29 at the depths indicated in the Summary of Water Levels below With the exception
of Boring B-24 which was destroyed on-site and the borings previously listed the remainder of
the borings were dry at day Hole cave-in depths at day ranged
between 11.7 and 30.6 feet
below the existing ground surface Hole cave-in may be an indication of water present
Subsurface water 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 during this study
SUMMARY OF WATER LEVELS
Boring No Depth to Water Day
ft
B-13 Dry
B-14 Dry
B-15 Dry
B-16 Dry
B-17 Dry
B-18 Dry
B-19 11.3
B-20 16.7
B-2l 9.9
B-22 17.2
B-23 21.0
B-24 Hole Destroyed
B-25 19.3
B-26 19.4
B-27 20.8
B-28 Dry
B-29 18.4
B-30 Dry
B-31 Dry
Report of Subsurface Exploration
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall
ESP Project No E4-UD42.302
July 2007
Report of Subs urface Exploration ESP Project No E4-UD42 302
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
4.0 CONCLUSIONS AND RECOMMENIATIONS
4.1 GENERAL
Our conclusions and recommendations are based on the project information previously discussed
and on the data obtained from the field and laboratory testing program If the structural loading
geometry or proposed buildrng locations are changed or significantly differ from those discussed
or if conditions are encountered during construction that differ from those encountered by the
borings ESP requests the opportunity to review our recommendations based on the new
information and make any necessary changes
4.2 SITE DEVELOPMENT
The results of the field testing program and analyses indicate that the majority of the property
appears to be suitable for constructing lightly to moderately loaded structures provided the
following measures are considered
4.2.1 BUILDING 13
The results of the field testing program and analysis indicate that the proposed Building 13 area
appears to be suitable for constructing moderately
loaded structure provided the following
measures are considered
Borings B-14 B-17 and B-18 encountered partially weathered rock PWR at
depths ranging
between 14.5 and 21 feet below the existing ground surface
Boring B-14 encountered auger refusal within the PWR at depth of 15 feet
below the existing ground surface Also Boring B-16 encountered auger refusal
within the residuum at depth of 21.1 feet We recommend that the depth to the
PWR and/or auger refusal be considered when establishing final grades and
evaluating grading challenges
Difficult excavation should be anticipated in areas
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Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
of the building pad to be cut more than 15 feet If the entire foundation area is not
bearing on rock or PWR then any rock pinnacles or sections encountered within
feet from the proposed bottom of foundation elevation should be removed and
replaced with cushion of compacted structural fill soil The depth of and need
for cushion material should be determined in the field by representative of the
geotechnical engineer
Variable density fill soils were encountered in Boring B-18 The fill extended to
depth of approximately 9.5 feet blow the existing ground surface We
recommend that any existing fill soils encountered within the proposed building
pad be removed and replaced with compacted structural fill
4.2.2 BUILDING 21
The results of the field testing program and analyses indicated that the majority of the proposed
Building 21 area is not suitable for constructing moderately
loaded structure within the existing
soil conditions The following measures should be considered
Variable density fills soils were encountered in Borings B-l9 through B-22 and
B-24 The fill extended to depths ranging
between and 14 feet below the
existing ground surface Based on historical information that the area was
previously residential and industrial development and our observations it
appears that topographic elevations at the site have changed considerably along
the southern quadrant of the intersection of Dunbar and Clarkson Streets We
recommend that any existing utility lines fill soils or foundations be removed
from the proposed building area
Lower consistency residual soils soils exhibiting N-values less than bpf were
encountered in Boring B-23 at depth of approximately 3.5 feet and extended to
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Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
feet below the existing elevation We recommend that any lower consistency
residual soils encountered in the upper feet below the proposed foundation
bearing elevation be removed prior to or during construction The lower
consistency soils should be evaluated in the field by representative of the
geotechnical engineer
High plasticity clay fill soils were encountered in Boring B-21 from to 5.5 feet
below the existing ground surface These materials undergo significant change in
volume shrink/swell with changes in their moisture content Because of this
evaluation by the geotechnical engineers representative should be performed
during construction to help reduce the potential of such materials from directly
underlying the building and pavement which could be affected by soil movement
Considering the need for potential undercut of approximately 14 feet below the
existing ground surface due to the presence of the existing fill soils and the water
levels in Borings B-19 and B-21 depths of 11.3 and 9.9 feet below existing
ground surface it is our opinion that groundwater could be encountered
temporary dewatering system may need to be installed in Building 21 during
undercutting of the existing fill soils Recommendations regarding dewatering
system will be addressed in subsequent sections of this report
4.2.3 BUILDING 23
The results of the field testing program and analyses indicate that the majority of the proposed
Building 23 area is not suitable for constructing moderately
loaded structure within the existing
soil conditions The following measures should be considered
Variable density fill soils were encountered in Borings B-25 through B-30 The
fill extended to depths ranging between and feet below the existing ground
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Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
surface It was observed that the fill material in Boring B-26 contained
concrete debris to depth of 5.5 feet below the existing ground surface We
recommend that all existing fill material be removed from the proposed building
area
Lower consistency residual soils soils exhibiting N-values less than bpf were
encountered in Boring B-29 at depth of 5.5 feet and extended to approximately
feet below the existing elevation We recommend that any lower consistency
residuals soils encountered in the upper feet below the proposed foundations
bearing elevation be removed prior to or during construction The lower
consistency soils should be evaluated in the field by representative of the
geotechnical engineer
4.3 EXISTING FILL
Results from the soil test borings performed
at the site indicate that fill soils are present in
Borings B-18 through B-22 and B-24 through B-30 The fill extends to depths varying
between
to 14 feet below the existing ground surface Standard Penetration Resistances N-values
obtained in the fill ranged from to 15 bpf Based on our visual observations of the split-spoon
samples recovered and our boring observations the fill encountered at Boring B-26 contained
concrete debris All other fill material encountered in the borings appeared to be clean of
concentrated organics debris and other deleterious materials However additional fill soils
containing debris should be expected due to the presence of buried foundations that were
encountered and discussed in ESPs Report of Preliminary Subsurface Exploration dated May
26 2006 Based on the soil boring data and visual observations it appears that the majority of
the existing fill is present across the portion of the site located west of Cedar Street It should
also be noted that two other areas with existing fill have been observed on the southern side of
the proposed Building 13 Existing fill may be encountered in other areas of the site not
observed by ESP
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Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
Due to the limited testing performed and the wide spacing of borings the possibility of
deleterious inclusions and variable density material in or under the existing fill is likely Since
the fill encountered was variable density and contained concrete debris at select locations
excessive settlement will likely result if built upon causing building and slab on grade
distress Also the presence of the existing fill beneath pavement areas presents risk of increased
settlement and subsequently possible increased long term maintenance of the pavement areas
These conditions are not considered acceptable for buildings therefore several options should
be considered These options may include remove the existing fill and replace with
compacted suitable structural fill extend the foundations through the existing fill to bear on
competent residual soils or use of deep foundations to support the structures To reduce the
risk imposed by
the existing fill additional evaluations including test pit excavations ground
penetrating radar hand-auger borings with Dynamic Cone Penetrometer tests proofrolling
and/or additional soil test borings could be performed to further evaluate the character and
continuity of the fill Based on our discussions with Mr Jade Eastridge we understand that
Beazer will likely implement Option No within the building areas therefore detailed
recommendations regarding deep foundations are not included in this report If the owner
chooses to allow the existing fill to remain in place beneath the pavements thorough field
evaluation should be performed by representative of the geotechnical engineer
at the time of
construction
4.4 PRELIMINARY FOUNDATION SUPPORT
For satisfactory performance the foundation for any structure must satisfy two independent
design criteria First it must have an acceptable factor of safety against bearing failure of the
foundation soils under the maximum design loads Second the settlement of the foundations due
to consolidation of the underlying soils should be within tolerable limits for the structures
Based on the results of the soil test borings the proposed structures can be adequately supported on
shallow foundations bearing on firm low-plasticity residual soils and/or newly placed suitable
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Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall July 2007
structural fill provided the site development site preparation and fill placement procedures outlined
in this report are implemented For Buildings 13 21 and 23 net allowable bearing pressure of
3000 2000 and 2000 pounds per square
foot psf respectively can be used for design of the
foundations bearing on residual soils exhibiting N-values of bpf or greater for 3000 psf and bpf
or greater for 2000 psf or on structural fill material compacted to at least 95 percent of the soils
Standard Proctor maximum dry density
The retaining walls located to the east of Dunbar Street
can be designed for net allowable bearing pressure of 4000 psf if bearing on residual soils
exhibiting N-values of 14 bpf or greater
Old existing fill soils were encountered in Borings B-18 through B-22 and B-24 through B-30 to
depths ranging from feet to 14 feet below the existing elevation As previously stated since
portions of the fill material encountered were of variable density and contained construction debris
unacceptable settlement will likely result causing building distress Due to the risk of
increased settlement it is not considered acceptable for the foundations to bear upon the
existing fill materials containing the above materials The three alternatives as outlined in
Section 4.3 should be considered for building support The above noted bearing capacities assumes
removal of all existing fill soils and replacement with clean properly compacted structural fill
Minimum wall and column footing dimensions of 18 and 24 inches respectively should be
maintained to reduce the possibility of localized punching-type shear failure Exterior
foundations and foundations in unheated areas should be designed to bear at least 18 inches
below finished grade for frost protection
Based on the general stratigraphy in the building areas past experience with similar projects and the
anticipated magnitude of the building loads it is our opinion
that the total and differential settlement
potentials within firmer residual soils and/or newly placed structural fill for Buildings 13 and 21
should be on the order of inch and /2 inch respectively Total and differential settlement
potentials within firmer residual soils and/or newly placed structural fill for Building 23 should be
on the order of inch and inch respectively Based on information obtained from Mr Kraig
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Klaussen with Echelon Engineering these settlements are tolerable for the buildings in question
These conclusions are contingent upon all existing fill material being undercut and replaced in
accordance with the site preparation and fill placement recommendations outlined in this
report and in our previous preliminary subsurface exploration report
4.5 FLOOR SLABS
Slab-on-grade floor systems can be adequately supported on firm low-plasticity residual soils or
newly placed structural fill provided the previously discussed site development issues are
addressed and the site preparation and fill placement procedures outlined in this report are
implemented If the floor slabs are designed as typical slabs-on-grade they should be
completely isolated from the structural components to allow independent movements of the slabs
and building foundations Slabs constructed above the unsuitable existing fill soils should be
structurally supported by the buildings foundation system
Immediately prior to constructing the floor slabs we recommend the areas be proofrolled to
detect unstable areas that may have been exposed to wet weather or construction traffic Areas
that are found to be unstable or indicate pumping action during the proofrolling should be
undercut and replaced with adequately compacted structural fill The proofrolling should be
observed by representative of the geotechnical engineer
4.6 FOUNDATION WALLS
We understand that foundation shear walls will be constructed along select portions of Building
13 where cut is anticipated Similarly foundation shear walls are planned for portions of
Buildings 21 and 23 where undercut of the existing fill soils has been recommended Based on
information obtained from Mr Malcolm Foss with Echelon Engineering the perimeter shear
walls and the shear walls at the center of the buildings near the elevator will extend
approximately feet and feet respectively
below FFE to the bottom of the shear wall
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foundation We recommend that the foundation walls be designed with regard to the lateral
pressure exerted by the compacted backfill We recommend that the At rest lateral earth
pressure coefficient be used if the wall is retrained from rotation and that the Active lateral
earth pressure coefficient be used if rotation is not restrained The lateral earth pressure
coefficients are based on conservatively estimated angle of internal friction for compacted
backfill and the on-site soils based on our experience with similar materials and our laboratory
testing program We recommend the following At rest lateral earth pressures K0 Active
lateral earth pressures Ka and Passive earth pressures Kr provided on the following chart
be used in conjunction with soil backfill wet unit weight of 130 pounds per cubic foot jcf
FOUNDATION WALL DESIGN P4RAMETERS
Net AllowableLocationWestUnit
Bearing Sliding Friction
Wt pcf Pressure Coeff Tan
psf
Building 13 0.33 3.0 0.50 130 3000 0.34
Building2l 0.38 2.7 0.55 130 2000 0.31
Building23 0.38 2.7 0.55 130 2000 0.31
Note Results are based on evaluations and analyses from ESP Soil Test Borings B-13 to B-31
In addition to the lateral loads exerted by the soil against the walls allowance should be included
for lateral stresses imposed by any temporary or long-term surcharge loads
Foundation drains should be installed behind the foundation walls to provide drainage
and
reduce build-up of hydrostatic forces free draining granular
material or manufactured product
such as Mirafi HC Drain or approved equivalent should be placed directly against the foundation
walls and tied to the foundation drains Foundation drain pipes should be connected to storm
drain located near the building and positive drainage should be provided at all times
In backfilling against the walls care should be taken to prevent the backfill from being over
compacted as this could result in excessive lateral stresses against the walls In the same regard
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heavy equipment should not be used for the compaction of the fill or operated adjacent
to the
walls
4.7 CUT AND FILL SLOPES
For landscaping and mowing concerns final project slopes
should be designed to be horizontal
to vertical or flatter Slopes can generally be designed as steep as horizontal to vertical
however erosion and slope maintenance should be expected The tops and bases of all slopes
should be located minimum of 10 feet from structural and feet from pavement limits The fill
slopes should be adequately compacted as outlined below and all slopes should be seeded and
maintained after construction
Two retaining walls double-tier are planned to support the cut face of the area located to the
southeast of Dunbar Street near Building 13 We recommend that the retaining walls be
designed with regard to the lateral pressure exerted by the compacted fill We recommend that
the Active and Passive lateral earth pressure coefficients shown in the following chart be
used in conjunction with soil backfill wet unit weight of 130 pcf In addition to the lateral
loads exerted by the soil against the walls allowance should be included for lateral stresses
imposed by any temporary or long-term surcharge loads
RETAINING WALL DESIGN PARAMETERS
Net AllowableLocationK0K0WetUnit
Bearing Sliding Friction
Wt pcf Pressure Coeff Fan
psf
Retaining 3.0 N/A 130 4000 0.55Wall
Retaining wall analysis was not part of our scope of services However any retaining wall
should be designated using appropriate
soil parameters based on the site and construction
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conditions Also any walls designed must be properly analyzed by the wall design engineer
with respect to global stability analysis and other design parameters
5.0 CONSTRUCTION CONSIDERATIONS
5.1 EXISTING UTILITIES
Based on review of the site drawing titled West End Density Study City of Charlotte NC
dated April 12 2006 provided to us by Beazer Homes and our visual observations during the
subsurface exploration no underground utilities are known to exist in the areas of Buildings 13
21 23 or the proposed retaining walls However if existing lines are encountered we
recommend all lines be removed and relocated outside of the proposed building areas
Additionally all trench backfill material if encountered should be removed and the subgrade in
all trench excavations be evaluated by representative of the geotechnical engineer prior to
backfihling The subgrade evaluation should consist of visual observations probing
with steel
rod andlor performing hand auger borings with Dynamic Cone Penetrometer tests to evaluate
their suitability for receiving structural fill Once all trenches are evaluated and approved they
should be monitored and backfilled with adequately compacted structural fill compacted to
minimum of 95 percent of the Standard Proctor maximum dry density
value
5.2 SITE PREPARATION
The entire building and pavement areas should be stripped of all topsoil organic soils soft near
surface soils trash debris and other organic materials if encountered to minimum of 10 feet
beyond the structural limits Upon completion of the stripping operations the exposed subgrade
in areas to receive fill should be proofrolled with loaded dump truck or similar pneumatic tired
vehicle minimum loaded weight of 20 tons under the observation of representative of the
geotechnical engineer The proofrolling procedures should consist of four complete passes of the
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exposed areas with two of the passes being in direction perpendicular to the preceding ones
After excavation of the site has been completed the exposed subgrade
in cut areas should also be
proofrolled as previously described Any areas which deflect rut or pump excessively during
proofrolling or fail to improve sufficiently after successive passes should be undercut to suitable
soils and replaced with structural fill
Variable density fill soils were observed in Borings B-18 through B-22 and B-24 through B-30
Concrete debris was encountered in Boring B-26 Due to the limited testing performed and the
wide spacing of borings the possibility of deleterious inclusions and variable density material in
other areas of the site is likely These materials should be removed from structural areas if
shallow foundations are to be constructed
5.3 TEMPORARY EXCAVATION STABILITY
Excavations greater than four feet in depth should be sloped or shored in accordance with local
state and federal regulations including OSHA Construction Standard for Excavations 29
CFR Part 1926 The contractor is usually solely responsible for site safety This information is
provided only as service and under no circumstances should ESP be assumed to be responsible
for construction site safety
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5.4 DIFFICULT EXCAVATION
5.4.1 BUILDING 13
Based on the provided FFE of 691.33 at Building 13 it appears that Borings B-13 through B-18
are located in cut areas
BUILDING 13
ProposedBoringNoExistingElevationFFECut-IFill Depth Auger Refusal Depth
ftft
B-13 705.8 691.33 -14.47 N/A
B-14 705.8 691.33 -14.47 15.0
B-15 702.6 691.33 -11.30 N/A
B-16 702.6 691.33 -11.30 21.1
B-17 702.6 691.33 -11.30 N/A
B-18 699.0 691.33 -7.70 N/A
It appears that the majority of the residual soil can be excavated using pans scrapers backhoes
and front end loaders However Boring B-14 encountered PWR that appears to be excavatable
to depth of 15 feet below the existing ground surface where auger refusal was encountered
Boring B-16 was terminated upon auger refusal at depth of 21.1 feet Therefore we anticipate
that partially weathered rock intermittent rock lenses andlor boulders will be encountered during
general site grading and excavation for the installation of footings and utilities Blasting would
likely be necessary in these areas in order to remove the material below FFE at Boring B-14
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Report of Subsurface Exploration
Morehead CommonBuildings 13 21 and 23 and Proposed Retaining Wall
5.4.2 BUILDING 21
ESP Project No E4-UD42 302
July 2007
Based on the provided FFE of 669.33 it appears that Borings B-19 through B-24 are located in
fill areas The PWR encountered at Boring B-21 appears to be excavatable to depth of
approximately 18.8 feet below the existing ground elevation where auger refusal on PWR was
encountered
BUILDING 21
ProposedBoringNoExistingElevationFFECut Auger Refusal Depth
ftDepth
ft
B-19 667.5 669.33 1.83 N/A
B-20 662.5 669.33 6.83 N/A
B-21 668.0 669.33 1.33 18.8
B-22 668.5 669.33 0.80 N/A
B-23 666.5 669.33 2.83 N/A
B-24 668.5 669.33 0.83 N/A
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Report ofSubsurface Exploration
Morehead Common Buildings 13 21 and 23 and Proposed Retaining Wall
5.4.3 BUILDING 23
ESP Project No E4-UD42.302
July 2007
Based on the provided FFE of 660.0 it appears that Borings B-25 through B-30 are either near
the FFE or located in fill areas PWR was not encountered in these borings
5.4.4 RETAINING WALL
BUILDING 23
Based on the provided bottom of wall elevation of 688.5 feet Boring B-3 is located in cut
area The PWR encountered appears to be excavatable to depth of approximately 27 feet
below existing elevation where the boring was terminated
_________RETAINING WALL
ProposedBoringNoExistingElevationFFECutOFilI Auger Refusal Depth
ftDepth
ft
B-31 706.5 688.5 -18 N/A
ProposedBoringNoExistingElevationFFECut-fFilL Auger Refusal Depth
ftDepth
ft
B-25 658.0 660.0 2.0 N/A
B-26 660.0 660.0 N/A
B-27 660.0 660.0 N/A
B-28 658.8 660.0 1.2 N/A
B-29 658.0 660.0 2.0 N/A
B-30 658.4 660.0 1.6 N/A
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The depth to and thickness of PWR and rock lenses or seams can vary dramatically in short
distances and between boring locations therefore
PWR or bedrock may be encountered during
construction at locations or depths between boring locations not encountered during this
exploration
It has been our past experience in this geologic area that materials having Standard Penetration
Resistances of less than 50 blows per 0.4 foot can generally be excavated using pans and
scrapers by first loosening with ripper attached to suitable sized dozer such as Caterpillar
D-8 or D-9 On earthwork projects requiring ripping questions sometimes develop as to whether
the materials can be removed by ripping or whether blasting is required It should be noted that
ripping is dependent upon finding the right combination of equipment and techniques used as
well as the operators skill and experience The success of the ripping operation is dependent on
finding the proper combinations for the conditions encountered Excavation of the weathered
rock is typically much more difficult in confined excavations Jackhammering or blasting is
anticipated to be required for materials having Standard Penetration Resistances in excess of 50
blows per 0.2 foot
We would like to point out that our experience indicates rock in weathered boulder and
massive form varies erratically in location and depth in the Piedmont Geologic Province
which
contains Charlotte North Carolina Therefore there is always potential that these materials
could be encountered at shallow depths between the boring locations
5.5 FILL MATERIAL AND PLACEMENT
All fill used for site grading operations
should consist of clean free of orgariics and debris
lower plasticity soil Plasticity Index less than 30 The proposed fill should have maximum
dry density of at least 90 pounds per cubic foot as determined by Standard Proctor compaction
test ASTM 698 All fill should be placed in loose lifts not exceeding inches in thickness
and compacted to minimum of 95 percent of its Standard Proctor maximum dry density
with
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100 percent achieved at the surface We recommend that field density tests including one-point
Proctor verification tests be performed on the fill as it is being placed at frequency determined
by an experienced geotechnical engineer
to verify the compaction criteria
Based on our experience and exploration of the project site the majority of the residual soils
encountered appear suitable to use as structural fill If low unit weight soils are encountered
during grading mixing with higher unit weight soils or increased compaction effort will be
required Also gravel was observed along the surface of portions of the site Based on
the size
of the gravel that we observed across several sections of the site these materials appear suitable
for use as structural fill In addition the majority of the existing fill observed appeared to be
clean and free of deleterious material therefore
it should be suitable for re-use as structural fill
We anticipate that some moisture conditioning of the on-site soils will be required if they are re
used as structural fill
5.6 TEMPORARY BEWATERING
Based on existing ground surface elevations stabilized groundwater levels and the recommended
undercut depth we anticipate that dewatering will be required at Building 21 We expect that
dewatering could be adequately handled with pumping from sumps excavated at least feet
below the bottom of the excavations Pumping from the sumps should be maintained until fill
placement in the excavation is minimum of feet above the water level At no time should
pumping be performed directly beneath the exposed subgrade
elevation since this could result in
disturbance of the bearing materials and loss of soil strength and increased settlement
5.7 SLOPING OF BUILDING PADS
We recommend that all building pads be sloped at final grade to allow for drainage during
inclement weather The silty soils present at the site are extremely moisture sensitive If the pads
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are not properly sloped at final subgrade inclement weather could result in excessive softening
of the subgrade soils
6.0 LIMITATIONS OF REPORT
This report has been prepared in accordance with generally accepted geotechnical engineering
practice with regard to the specific conditions and requirements of this site The conclusions and
recommendations contained in this report were based on the applicable standards of our practice
in this geographic area at the time this report was prepared No other warranty expressed or
implied is made
The analysis and recommendations submitted herein are based in part upon the data obtained
from the subsurface exploration The nature and extent of variations between the borings and
test pits will not be known until construction is underway If variations appear evident then we
request the opportunity to re-evaluate the recommendations of this report In the event that any
changes in the nature design or location of the structures are planned the conclusions and
recommendations contained in this report will not be considered valid unless the changes are
reviewed and conclusions modified or verified in writing by ESP
In order to verify that earthwork and fOundation recommendations are properly interpreted and
implemented we recommend that ESP be provided the opportunity to review the final plans and
specifications Any concerns observed will be brought to our clients attention in writing
26
FIELD EXPLORATION PROCEDURES
Soil Test Boring Nineteen 19 soil test borings were drilled at the approximate locations
shown on the attached Boring Location Plan Figure Soil sampling and penetration testing
were performed in accordance with ASTM 1586
The borings were advanced with hollow-stem augers and at standard intervals soil samples
were obtained with standard 1.4-inch I.D 2-inch O.D split-tube sampler The sampler was
first seated six inches to penetrate any loose cuttings then driven an additional foot with
blows of 140-pound hammer falling 30 inches The number of hammer blows is designated the
Standard Penetration Resistance When properly evaluated the Standard Penetration
Resistances provide an index to soil strength relative density and ability to support foundations
Select portions of each soil sample were placed in sealed containers and taken to our office The
samples were examined by representative of the geotechnical engineer for classification Test
Boring Records are attached showing the soil descriptions and Standard Penetration Resistances
Undisturbed Sampling Split-spoon samples obtained during penetration testing are suitable
for visual examination and classification tests but are not sufficiently intact for quantitative
laboratory testing Three relatively undisturbed samples were obtained by forcing section
of three-inch O.D 16 gauge steel tubing into the soil at the desired sampling levels This
sample procedure is described by ASTM Designation D-1587 The tube together with the
encased soil was carefully removed from the ground and made airtight The locations and
depths of undisturbed samples are shown on the appropriate Test Boring Records
LABORATORYPROCEDURES
Gram Size Test Grain size tests were performed to determine the particle size and distribution
of the samples tested The grain size distribution of soils coarser than No 200 sieve was
determined by passing the samples through set of nested sieves
The soil particles passing the
No 200 sieve were suspended in solution and the grain size distribution determined from the rate
of settlement
The results are presented on the attached Grain Size Distribution Sheets
Soil Plasticity Tests Atterberg Limits Test Select samples were identified for Atterberg
Limits testing to determine the soils plasticity characteristics The Plasticity Index PT is
representative of this characteristic and is determined utilizing the Liquid Limit LL and the
Plastic Limit PL The Liquid Limit is the moisture content at which the soil will flow as
heavy viscous fluid and is determined in accordance with ASTM 4318 The Plastic Limit is
the moisture content at which the soil begins to lose its plasticity and is determined in accordance
with ASTM D4318 The data obtained is presented on the attached Summary of Laboratory Test
Data sheet
Consolidation Test Single sections of selected undisturbed samples were extruded from the
sampling tubes for consolidation testing Each section was trimmed into disc 2.5 inches in
diameter and inch thick The disc was confined in stainless steel ring and sandwiched
between porous stones The sample was then subjected to incrementally increasing
vertical loads
and the resulting deformations measured with micrometer dial gauge The results were
presented in the form of pressure versus percent strain curve on the accompanying
Consolidation Test Sheets
Standard Proctor Compaction Test Select samples of the on-site soils were obtained from
auger cuttings to determine their suitability as fill material Standard Proctor Compaction Tests
ASTM 698 were performed on these soils to determine their compaction characteristics
including maximum dry density and optimum moisture content The test results are presented on
the attached Compaction Test Sheets included in the Appendix
Triaxial Compression Test In triaxial test cylindrical specimen is subjected to an equal
all-around pressure and in addition to an axial cylindrical surface of the sample is covered by
rubber membrane sealed to pedestal at the bottom and to cap at the top The assemblage is
contained in chamber into which water may be admitted under any desired pressure this
pressure acts laterally on the cylindrical surface of the sample through the rubber membrane and
vertically through the top cap The additional axial loads is applied by means of piston passing
through the top of the chamber
Porous disks are placed against the top and bottom of the sample and are connected to the
outside of the chamber by tubing By means of these connections the pressure of the water
contained in the pores of the sample can be measured if drainage is not allowed Alternatively if
flow is permitted through these connections the quantity of water passing into or out of the
sample during the test can be measured As the loads are increased the vertical deformation of
the specimen is measured by dial gage All tests are conducted by holding the all-around
pressure constant and increasing the vertical pressure