HomeMy WebLinkAboutSubsoils Study for Foundation Designrc flffilflffiffii$fd-*
An Fm&pc eh,nncd C0mpony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Spnngs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE AIYD BARN/ADU
999 COUNTY ROAD 238
GARFIELD COUNTY, COLORADO
PROJECT NO.22-7-719
JA|IUARY 11,2023
PREPARED FOR:
BEN WAGENMAN
126 COUNTY ROAD 238
srLT, coLoRADO 81652
oleoconstruction@ gmail.com
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION ..
SITE CONDITIONS
FIELD EXPLORATION .........
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM .......
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 through 7 - SWELL-CONSOLIDATION TEST RESULTS
TABLE I- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. @ Project No. 22-7-719
PURPOSE A}[D SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence and barn/ADU to be
located at999 County Road 238, Garfield County, Colorado. The project site is shown on
Figure 1. The pu{pose of the study was to develop recommendations for the foundation design.
The study was conducted in accordance with our agreement for geotechnical engineering
services to Ben Wagenman dated November 7,2022.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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 2-story structure with a walkout lower level and the barn/ADU
will be a pole structure located as shown on Figure 1. Ground floors will be slab-on-grade.
Grading for the structures is assumed to be relatively minor with cut depths of about 2 to 8 feet.
We assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, locations 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 property was vacant and covered with about 4 inches of snow at the time of our field
exploration. The ground surface has a strong slope down to the south with around 3 feet of
elevation difference across each building footprint. Vegetation consists of mostly grass and
weeds with pinon and juniper trees along the building area perimeter. Large remnant sandstone
blocks were observed near the residence site.
The field exploration for the project was conducted on December 28,2022. Three exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
Kumar & Associates, lnc. @ Project No. 22'7-719
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The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of Kumar &
Associates-
Samples of the subsoils were taken with a 2-inch I.D. spoon sampler. The sampler was driven
into the subsurface materials at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test descibed by ASTM Method D-1586
The penetration resistance values are an indication of the relative density or consistency of the
subsoils and hardness of the bedrock. 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 encountered, below aboutYz foot of topsoil, consist of medium dense, silty sand
overlying medium hard and weathered to very hard sandstone below depths of about 4 feet at
Boring I and 12 feet at Boring 2 in the residence site. ln the barn site, medium dense silty sand
was encountered down to about 12 feet and underlain by clayey sand down to the boring depth of
21feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the sand soils and weathered
sandstone, presented on Figures 4 through 7, indicate low to moderate compressibility under
loading and minor collapse potential (settlement under constant load) when wetted. The
laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsurface moterials
were moist to slightly moist with depth.
DESIGN RECOMMENDATIONS
FOIJNDATIONS
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 granular soils or bedrock.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
Kumar & Associates, lnc. @ Project No. 22-7-719
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1)Footings placed on the undisturbed natural granular soils should be designed for
anallowablebearingpressureo@Basedonexperience,weexpect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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 lea:!1l@hes-bplow exterior grade is typically used in this
area.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12feet.
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.
The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the natural granular soils. The exposed soils in
footing area should then be moistened and compacted. If water seepage is
encountered, the footing areas should be dewatered before concrete placement.
A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
5)
FOI'NDATION 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 50 pcf for backfill consisting
of the on-site granular soils. Cantilevered retaining structures which are separate from the
structure and can be expected to deflect sufficiently to mobilize 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 40 pcf for backfill consisting of the on-site granular soils.
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
2)
3)
4)
6)
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Kumar & Associates, lnc. @ Project No. 22-7-719
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Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at near optimum moisture content. Backfill placed 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
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 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 375 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
95Yo of the maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils or bedrock, 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 free-draining gravel should be placed beneath basement level slabs to facilitate drainage
This material should consist of minus Z-inch aggregate with at least 507o retained on the No. 4
sieve and less thon 2% passing thc No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at leastg5Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
onsite granular soils devoid of vegetation, topsoil and oversized rock.
TINDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow that local perched groundwater can develop during times
Kumar & Associates, lnc. @ Project No. 22-7-715
5
of heavy precipitation or 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 I foot below lowest adjacent finish grade and sloped at a minimum lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%opassing 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 llzfeet deep.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after each structure has been completed:
1) Inundation ofthe 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 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90%o 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
covered with filter fabric and 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 inigation should be located at least
5 feet from foundation walls.
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.
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
Kumar & Associates, lnc. @ Project No. 22-7-7'19
-6-
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 e,ncountered
during construction appear different from those desqibed 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 veri$ 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 shata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kumsr &
Steven L. P
Reviewed by:
Daniel E. Hardin, P.E.
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APPROXIMATE SCALE-FEET
LOCATION OF EXPLORATORY BORINGS Fig. 122-7-719 Kumar & Associates
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BORING 1
EL. 100.0'
BORING 2
EL. 97.0'
BORING 5
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13/ 12
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22-7-719 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE.
11r<q DRIVE SAMPLE BLOW COUNT. INDICATES THAT 11 BLOWS OF A I/+O-POUND HAMMER"/ '' FALLTNG Jo tNcHES wERE REeUIRED To DRtvE THE SAMpLER 12 lNcHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 28, 2022 WITH A 4.INCH DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PTAN PROVIDED AND BUILDING LOCATIONS PROVIDED BY
THE CLIENT.
5. THE ELEVATIONS OF EXPLORATORY BORINGS 1 AND 2 WERE MEASURED BY HAND LEVEL AND
REFER TO BORING 1 AS 'IOO, ASSUMED ELEVATION OF BORING 5 WAS NOT DETERMINED.
1. 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 (X) (ASTM D2216);
DD = DRY DENSITY (PCt) (ISTU D2216);
-2OO = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
LEGEND AND NOTES Fig. 322-7-719 Kumar & Associates
SAMPLE OF: Sllty Sond
FROM:Borlng1O2.5'
WC = 17.3 )a, DD = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SAMPLE 0F: Wcqthcrcd Sondstonc
FROM:BorlnglO5'
WC = 5.1 X, DD = 128 pci
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SAMPLE OF: Silty Sond
FROM:Borlng2O5'
YIC = 1.2 X, DD = 100 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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22-7-719 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 6
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SAMPLE 0F: Sllfy Sond
FROM:BorlngSO5'
WC = 4.6 X, DD = 108 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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Fis. 7SWELL-CONSOLIDATION TEST RESULTS22-7 -7 19 Kumar & Associates
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SATIFL LOClnOtl ITIFPI LtttTs
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STREIIGTH SOILTYPE
I 2Y2 17.5 100 Silty Sand
5 5.1 128 Weathered Sandstone
2 5 4.2 100 Silty Sand
l0 4.9 ll5 35 Silty Sand
J 2%4.1 109 35 Silty Sand
5 4.6 108 Silty Sand
Itlo.22-7-719