HomeMy WebLinkAboutSubsoil Study for Foundation Design 09.21.2020IC+A
Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ). Parker. Colorado Springs. Fort Collins. Glenwood Springs. and Summit Count). Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
TWO PROPOSED RESIDENCES
35 ACRE PARCEL NO. 217729100011
EAST OF RIFLE VILLAGE SOUTH
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-434
SEPTEMBER 21, 2020
PREPARED FOR:
JOSE SALAZAR
26 NATIVE SPRINGS DRIVE
RIFLE, COLORADO, 81650
salazareservices(c�gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FLOOR SLABS - 4 -
UNDERDRAIN SYSTEM - 4 -
SURFACE DRAINAGE - 4 -
LIMITATIONS - 5 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 & 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 20-7-434
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for two proposed residences to be located on
the subject site. The project site is shown on Figure 1. The purpose of the study was to develop
recommendations for the foundation design. The study was conducted in accordance with our
proposal for geotechnical engineering services to Jose Salazar dated July 29, 2020.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the field
exploration were tested in the laboratory to determine their classification, compressibility or
swell and other engineering characteristics. The results of the field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and allowable
pressures for the proposed building foundation. This report summarizes the data obtained during
this study and presents our conclusions, design recommendations and other geotechnical
engineering considerations based on the proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
The proposed residences will be one and two-story wood frame structures located in the area of
Borings 1 and 2 as shown on Figure 1. Ground floor will be slab -on -grade. Grading for the
structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We
assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The 35 -acre property is vacant of structures. The building sites had been stripped of vegetation.
Surrounding areas were vegetated with grass and sage brush. The general topography is gently
sloping down to the north. Adjoining properties to the south and west of Boring 2 were
developed with residences.
Kumar & Associates, Inc. ° Project No. 20-7-434
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FIELD EXPLORATION
The field exploration for the project was conducted on August 11, 2020. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4 -inch diameter continuous flight augers powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with 1% inch and 2 -inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 1/2 foot of topsoil overlying 60 to 73 feet of medium dense, sand and silt.
Dense gravel soils were encountered in the borings at roughly the same elevation, 60 feet in
Boring 1 and 731/2 feet in Boring 2. Approximately 51/2 feet of sandy clay and silt soil was
encountered below the topsoil in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density, Atterberg limits testing and percent finer than sand size gradation analyses.
Results of swell -consolidation testing performed on relatively undisturbed drive samples,
presented on Figures 4 and 5, indicate low to moderate compressibility under conditions of
loading and wetting with a low expansion or collapse potential (settlement when wetted under
constant load) when wetted under a constant light surcharge. Results of percent finer than sand
size gradation analyses performed on small diameter drive samples of the sandy subsoils varied
from 38 to 76 percent. Atterberg limits testing indicates the clay and silt soils have low
plasticity. The laboratory testing is summarized in Table 1.
Kumar & Associates, Inc. 0 Project No. 20-7-434
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No free water was encountered in the borings at the time of drilling the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The subsoils at the two building sites have moderate bearing capacity and low to moderate
settlement potential. Due to the depth of the settlement -prone soils, future deep subsurface
wetting could result in excessive settlement, potentially causing distress and cracking of the
proposed houses. It will be critical to the long-term performance of the structures to keep the
subsoils from getting wet. Recommendations for site grading and routing of roof runoff away
from the building are provided in this report.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the buildings be founded with spread footings bearing
on the natural sand and silt soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 1,200 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footings should have a minimum width of 20 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 14 feet.
Kumar & Associates, Inc. ® Project No. 20-7-434
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Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
50 pcf.
5) All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the firm natural silt and sand soils.
The exposed soils in footing areas should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
construction. To reduce the effects of some differential movement, floor slabs should be
separated from all bearing walls and columns with expansion joints which allow unrestrained
vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage
cracking. The requirements for joint spacing and slab reinforcement should be established by the
designer based on experience and the intended slab use. A minimum 4 inch layer of gravel
should be placed beneath slabs for support. This material should consist of minus 2 -inch
aggregate with at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
We understand that the proposed slab -on -grade ground floors will be at or slightly above th
surrounding ground surface.
A perimeter underdrain system is not needed and we recommend
that it not be installed. The following recommendations for surface drainage around the
building exterior should be followed.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residences has been completed:
Kumar & Associates, Inc. ® Project No. 20-7-434
5
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill and water should not be allowed to pool within 10 feet of the foundations.
5) Landscaping which requires regular heavy irrigation should be located at least
10 feet from foundation walls. Consideration should be given to use of xeriscape
to reduce the potential for wetting of soils below the building caused by irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concerned about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during construction to review and
Kumar & Associates, Inc. ® Project No. 20.7-434
6
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumar & Associates, Inc.
Daniel E. Hardin, P.
DEH/kac
Kumar & Associates, Inc.Project No. 20-7-434
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APPROXIMATE SCALE—FEET
20-7-434
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
BORING 1
EL. 87.5'
0 24/12
-200=76
LL=22
P|=O
31/1231/12a / /' l WC=4.5
| DD=118
28/12
WC=4.6
DD=110
10 -200=68
` 24/12
WC=27
DD=117
-200=38
15
35/12
2O
25
30
50
36/12
_
_
_
---55
.44
27/12
YYC=3.3
DD=106
52/12
60
13/6. 50/4
—65
DEPTH -FEET
5
15
20
25
BORING 2
EL. 100'
10/12
�/- WC=3.7
/ n
_ n=111
-
17/12
WC=5y
DD=S7
' -200=54
9/12/ — WC=3.2
,� DD=97
:;>"/"
4;1 9/6, 15/6
35/6, 25/6
�C=2�8
�C2�8
-2OO=33
LL=17
y P|=2
53/12
30 WC=3.9
DD=110
5041/6, 50/6
55
— 70
75
50/2, 100/3.5
20-7-434
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
WIC
A
7
TOPSOIL; ROOTZONE, CLAYEY SANDY SILT, ORGANIC, STIFF, SLIGHTLY MOIST, BROWN.
CLAY AND SILT (CL—ML); SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN.
SAND AND SILT (SM—ML); SLIGHTLY CLAYEY TO CLAYEY LAYERS, OCCASIONAL GRAVELLY
LENSES, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS.
!'• GRAVEL (GM); SANDY, SILTY WITH COBBLES, VERY DENSE, SLIGHTLY MOIST, BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
24/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 24 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 11, 2020 WITH A 4—INCH—DIAMETER
CONTINUOUS—FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE PROVIDED BY THE CLIENT.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL WITH THE
GROUND ELEVATION AT BORING 2 ASSUMED TO BE ELEVATION 100 FEET.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140);
LL = LIQUID LIMIT (ASTM D4318);
PI = PLASTICITY INDEX (ASTM D4318).
20-7-434
Kumar & Associates
LEGEND AND NOTES
Fig. 3
CONSOLIDATION SWELL
CONSOLIDATION - SWELL
0
— 2
1
0
— 1
— 2
— 3
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 ® 5'
WC = 4.5 %, DD = 118 pcf
— EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF 10 100
TMH Mel MUlls apply only to the
eomplee Ssi(s Tm. Staling report
ehel not be dted, erupt In
full, without thehe written approval of
%oma. and Associates, Inc Swell
Caosal.detioa telling performed in
Ettordonct with n ted 1:1-454
SAMPLE OF: Clayey Silty Sand
FROM: Boring 1 ® 20'
WC = 3.3 %, DD = 106 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF 10 100
20-7-434
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fic
CONSOLIDATION SWELL
2
a
CONSOLIDATION - SWELL
1
—1
— 2
— 3
— 4
SAMPLE OF: Sandy Silt
FROM: Boring 2 0 2.5'
WC = 3.7 %, DD = 111 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 100
Thea Wet re.ute appy aaly to she
samples tailed. The seat+rQ repel
. hall not h• reproduced, eacrrp{ in
fell, without {he written approver of
K umar and M.oclofde, Inc. Swell
Con.otidatlon toiling performed In
accordance with ASTM 0-4540.
SAMPLE OF: Silty Sand
FROM: Boring 2 ® 10'
WC = 3.2 %, DD = 97 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
•\
1.0 APPLIED PRESSURE - KSF TO 100
20-7-434
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fia.
Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-434
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pct)
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(Psi)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL 1
(%)
SAND I
(%°)
LIQUID LIMIT
(%)
PLASTIC
(%)
1
0
4.2
76
22
8
Sandy Silty Clay
5
4.5
118
Sandy Silty Clay
7'/2
4.6
110
68
Sandy Silt
10
2.7
117
38
Clayey Silty Sand
20
3.3
106
Clayey Silty Sand
2
2'/2
3.7
111
Sandy Silt
5
3.9
97
54
Sandy Silty Clay
10
3.2
97
Silty Sand
20
2.8
39
17
2
Very Silty Sand
30
3.9
110
Silt and Sand