HomeMy WebLinkAboutSoils Report 10.11.2019Kumar & Associates, .°
Geotechnical and Materials Engineers
I
� and Environmental Scientists
Z.-
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kurnarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
878 COUNTY ROAD 227 (MILLER LANE)
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-548
OCTOBER 11, 2019
PREPARED FOR:
DESIREE ATTEBURY
195 NORTH MEADOW DRIVE
RIFLE, COLORADO 81650
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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-
FOUNDATION AND RETAINING WALLS - 4 -
FLOORSLABS -5-
UNDERDRAIN SYSTEM - 5 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No, 19-7-548
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located 878
County Road 227 (Miller Lane), Garfield County, Colorado. 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 Desiree Attebury dated September 13, 2019.
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 residence will be a two-story, wood frame structure over a walkout basement in
the approximate area of the borings shown of Figure 1. Grading for the structure is assumed to
be relatively minor with cut depths between about 6 to 10 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 lot was vacant at the time of our field investigation. The proposed building corners were
staked by others. The terrain slopes down to the south at an approximate 5% grade. The ground
surface was covered with grass. County Road 227 is to the west, agricultural fields are north,
south, and east of the site, and a small farm with several single -story structures is to the west.
Kumar & Associates, Inc. Project No. 19.7-548
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FIELD EXPLORATION
The field exploration for the project was conducted on September 24, 2019. 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'/s 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. Below
about one foot of topsoil, the subsoils consist of up to 3 feet of soft, slightly sandy silt overlying
5 to 7 feet of medium stiff to stiff, sandy silt and clay. The silt and clay soils were underlain by
up to 8 feet of medium dense silty to very silty sand and gravel in Boring 1, and loose to medium
dense, silty clayey sand to the maximum depth explored, 31 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and percent fines (percent passing the No. 200 sieve). Results of swell -consolidation
testing performed on relatively undisturbed drive samples, presented on Figure 4, indicate low
compressibility under conditions of loading and wetting. The laboratory testing is summarized
in Table 1.
Groundwater was encountered in Boring 2 at approximately 23 feet while drilling. The subsoils
were slightly moist to very moist.
Kumar & Associates, Inc. Project No. 19-7-548
3
FOUNDATION BEARING CONDITIONS
The soft, slightly sandy silt encountered in Boring 1 possesses a very low bearing capacity and a
moderate to high risk of settlement. The medium stiff to stiff silt and clay possess a low bearing
capacity and a low to moderate risk of settlement. The upper portions of the medium dense to
dense, silty, clayey sand or silty sand and gravel encountered below about 8 to 9 feet possesses a
moderate bearing capacity and a low risk of settlement. We recommend that the residence be
supported on shallow footings bearing on the medium stiff to stiff silt and clay or the medium
dense to dense sand/sand and gravel. The soft slightly sandy silt should be removed from the
building footprint.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the medium stiff to stiff natural silt and clay or relatively dense granular 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 2,000 psf. Footings placed on the undisturbed
natural silt and clay soils should be designed for an allowable bearing pressure of
1,500 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 18 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. 19-7-548
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Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) All existing fill, topsoil, soft silt, and any loose or disturbed soils should be
removed and the footing bearing level extended down to the relatively dense
natural granular soils or medium stiff to stiff silt and clay. The exposed soils in
footing area 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.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils and at least 45 pcf for backfill consisting of imported granular materials.
Cantilevered retaining structures which are separate from the residence and can be expected to
deflect sufficiently to tnobilize the full active earth pressure condition should be designed for a
lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf
for backfill consisting of the on-site soils and at least 35 pcf for backfill consisting of imported
granular materials.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least 95% of the maximum standard Proctor density. Care
should be taken not to overcompact the backfill or use large equipment near the wall, since this
could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
Kumar & Associates, Inc. ' Project No. 19-7-548
5
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger
than about 6 inches.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a granular material compacted to at least
95% of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil and soft silt, 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 free -draining gravel should be placed beneath basement level slabs to facilitate drainage.
This material should consist of minus 2 -inch aggregate with at least 50% retained on the No. 4
sieve and less than 2% 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 soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
Kumar & Associates, Inc. Project No. 19-7-548
6
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
recommend below -grade construction, such as retaining walls, crawlspace and basement areas,
be protected from wetting and hydrostatic pressure buildup by an underdrain system.
The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above
the invert level with free -draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to
a suitable gravity outlet. Free -draining granular material used in the underdrain system should
contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least 11/2 feet deep. An
impervious liner such as 20 mil PVC should be placed below the drain gravel in a trough shape
and attached to the foundation wall with mastic to keep drain water from flowing beneath the
house.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
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. Free -draining wall backfill should be
capped with about 2 feet of the on-site soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from foundation walls.
Kumar & Associates, Inc. Project No. 19-7-548
7
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
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.
Shane J. Robat, P.E.
Reviewed by:
Daniel E. Hardin, P.E.
SJR/kae
Kumar & Associates, Inc.
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Project No. 19.7-548
1
50 .0 100
APPROXIMATE SCALE -FEET
19-7-548
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
2
1
gig
d
DEPTH-FEET
0
- - 5
10
15
20
25
30
BORING 1
EL. 5414'
3/12
WC=17.1
'DD=100
-200=91
8/12
WC=13.3
DD=109
35/12
WC=4.6
DD=126
-200=12
25/12
WC=10.6
DD=126
-300=44
9/12
BORING 2
EL. 5412'
/1
5/12
WC=12.9
DD=102
8/12
WC=13.0
DD=116
-200=66
l 17/12
WC=11.3
DD=121
16/12
WC=14.7
DD=113
-200=68
15/12
10/12
0
5
10
20
25
30
r35 35
19-7-548
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
7
L
7
TOPSOIL; CLAY AND SILT, SANDY, ORGANICS, FIRM, MOIST, DARK BROWN.
SILT (ML); SLIGHTLY SANDY, SOFT, MOIST, BROWN, LOESS.
SILT AND CLAY (ML—CL); SANDY TO VERY SANDY, MEDIUM STIFF TO STIFF, MOIST, BROWN.
SAND AND GRAVEL (SM—GM); SILTY, DENSE, MOIST, MIXED BROWN.
SAND (SM—SC); SILTY, CLAYEY, SCATTERED GRAVEL, LOOSE TO MEDIUM DENSE, MOIST TO
VERY MOIST, BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
3/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 3 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
Q DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING.
DEPTH AT WHICH BORING CAVED FOLLOWING DRILLING.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 24, 2019 WITH A 4—INCH—DIAMETER
CONTINUOUS—FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM 02216);
DD = DRY DENSITY (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
19-7-548
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
—1
— 2
— 3
— 4
1
— 1
—2
—3
Theo tot f.6#6 mall' en0y to the
ze I.Inl.0.p Th. I. rt�q erpen
Wal . rat W (u# ead..,cpt lh
TOL whh6,A the seinen el of
m
Keor and i ocpt. , Incnc SSor
Cgandoetzlan with
ANN
p. -4546 In
6 n6N encs Ith AS1Y D-4546
SAMPLE OF: Very Sandy Clay and Silt
FROM: Boring 1 0 5'
WC = 13.3 %, DD = 109 pcf
1.0 APPLIED PRESSURE — KSF
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
10 100
SAMPLE OF: Silty, Clayey Sand with Gravel
FROM: Boring 2 @ 10'
WC = 11.3 %, DD = 121 pcf
1.0 APPLIED PRESSURE — KSF
NO MOVEMENT UPON
WETTING
10 100
19-7-548
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
Kumar
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
BORING { DEPTH
Irt)
NATURAL NATURAL
MOISTURE DRY
CONTENT DENSITY
I pe t)
GRADATION
GRAVEL 1 SAND
(%) (%)
ATTERBERG LIMITS
PERCENT
PASSING NO. LIQUID LIMIT
200 SIEVE
UNCONFINED
PLASTIC COMPRESSIVE
INDEX STRENGTH
(%) i psf)
Project No. 19-7-548
SOIL TYPE
1
2Y2 17.1 100
5
13.3
109
10
4.6
126
15
10.6
126
91
12
Slightly Sandy Silt
Very Sandy Clay and Silt
44
Silty Sand and Gravel
2
2'/2
5
Silty, Clayey Sand with
Gravel
12.9
13.0
102
116
10
15
11.3
14.7
121
113
68
Sandy Clay and Silt
Sandy Clay and Silt
Silty, Clayey Sand with
Gravel
Sandy Clay and Silt with
Gravel
1