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SUBSOIL STUDY
FOR FOTINDATION DESIGN
PROPOSED SIIOP BUILDING
252 COUNTY ROAD 167
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-171
MARCrr 26,2019
PREPARED FOR:
CATTLE CREEK MILLWORK
ATTN: TODD MCCANN
252 COUNTY ROAD 167
GLENWOOD SPRTNGS, COLORADO 81601
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY .
PROPOSED CONSTRUCTION .........
SITE CONDITIONS....
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS ...
DESIGN RECOMMENDATIONS .........,.......
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
SITE GRADING.,..............
SURFACE DRAINAGE...
LIMITATIONS..........
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2. LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4. GRADATION TEST RESULTS
TABLE I. SUMMARY OF LABORATORY TEST RESULTS
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K*mer & A*e**i*te*, Bnc.Fr*je*t N*. fS"?-1?€
PURPOSE AIID SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed shop building to be located at
252 CountyRoad 167, Garfield County, Colorado. Theproject site is shown on Figure 1. The
purpose ofthe study was to develop recommendations for the foundation design. The study was
conducted in accordance with our proposal for geotechnical engineering services to Cattle Creek
Millwork dated March 11,2019.
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, 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 shop will be a7,200 square foot, single-story structure. The structure will be a
steel frame and metal skin with a slab-on-grade floor. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 5 feet. We assume relatively light to
moderate 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 project site is currently developed with a wood frame building to the north and a metal
building to the east of the proposed shop building. The area of the proposed shop is currently a
gravel surfaces parking/storage area. The ground surface is relatively flat and gently sloping
across the site then slopes down at about Zhoizontal to I vertical grade along the western and
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southem edges of the property. The steep slopes could be covered with push-out fill and are
vegetated with mostly sparse grass and weeds. The area around the site is developed with light
industrial, commercial and residential buildings. Coryell Road is west of the site and Coryell
Ridge Road is south of the site.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the site. These rocks are a
sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of
gypsum and limestone. There is a possibility that massive gypsum deposits associated with the
Eagle Valley Evaporite underlie portions of the property. Dissolution of the gypsum under
certain conditions can cause sinkholes to develop and can produce areas of localized subsidence.
Sinkholes were not obserwed in the immediate area of the subject site. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on the site throughout the service life of the proposed structure, in our
opinion, is low; however, the owner should be made aware of the potential for sinkhole
development. If further investigation of possible cavities in the bedrock below the site is desired,
we should be contacted.
FIELD EXPLORATION
The freld exploration for the project was conducted on March 20,2019. Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
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, Inc.
Samples of the subsoils were taken with a 1% inch I.D. spoon sampler. The sampler was 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-l586. 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
Kum*r & Asse*8*tew, itl*.Fr*j**t ffi*. *$-?"1?t
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shown on the Logs of Exploratory Borings, Figure 2. T\e 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 ofabout %to lYzfeetofsilty, clayey, sandy gravel fill overlying natural slightly
silty, sandy gravel with cobbles and possible boulders. Drilling in the dense granular soils with
auger equipment was diffrcult due to the cobbles and possible boulders and practical auger
refusal was encountered at 12 feet in Boring 2.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus lYzinchfraction) of the coarse granular subsoils are shown on Figure 4. The
laboratory testing is summari zed in Table I .
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
FOUNDATION BEARING CONDITIONS
At assumed excavation depths, we expect the subgrade will consist of natural gravel soils. The
natural gravel soils at the site possess moderate bearing capacity, relatively low settlement
potential, and are considered competent bearing materials for the support of shallow foundations
and slabs-on-grade provided the gravels remain undisturbed during construction. The existing fill
is not considered suitable for the support of shallow foundations and slabs-on-grade, in its
current condition, potential compressibility and uncertain density. There is also potential for the
fill depth to increase along the top of the steep slope which should be further evaluated at the
time of conskuction.
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 natural granular soils.
K::mar & &ss*eief**, $nc,Fr*je*t S*.19"?-t?tr
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,500 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about I 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 10 feet.
Foundation walls acting as retaining structures (if any) 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 and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively dense natural granular
soils, The footings should set back from the steep slope face a minimum
horizontal distance of 8 feet. This could require the west perimeter footing to be
deepened below the minimum frost depth. 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 (if any) 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 45 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
l{um*r & Asso*iat*s, 8n*.Fr*j**t Ff*.'i*-Y"lY{
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condition should be designed for a lateral earth pressure computed on the basis of an equivalent
fluid unit weight of at least 35 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
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 95Yo of the maximum
standard Proctor density at a moisture content near optimum. 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 0.50. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 300 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
95oh of themaximum standard Proctor density at a moisfure content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of existing fill, are suitable to support lightly to moderately
loaded slab-on-grade construction. The existing filI can support the slab-on-grade after it has
been excavated and replaced, then compacted to 95% of the standard Proctor. To reduce the
K*mar & S,ss*c8*t*s, 8**.Pr*je*t S*. ,$$-?"l?t
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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 relatively well graded sand and gravel should
be placed beneath interior slabs for support. This material should consist of minus 2-inch
aggregatewith at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200
sleve.
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 ofvegetation, topsoil and oversized rock.
I.INDERDRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above the
surrounding grade. Therefore, a foundation drain system is not required. It has been our
experience in the area that local perched groundwater can develop during times 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 and basement
areas, be protected from wetting and hydrostatic pressure buildup by un underdrain and wall
drain system.
If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SITE GRADING
The risk of construction-induced slope instability at the site appears low provided the building is
located above the steep slope as planned and cut and fill depths are limited. We assume cut
depths for foundation construction will not exceed 5 feet. Fills should be limited to about 5 feet
and not extend onto the steep downslope along the west and south sides of the building.
Embankment fills should be compacted to at least 95oh of the maximum standard Proctor density
Kurnsr & Ass*clet*c, lnc.Fr*j*e{ S*,'t$-?"{Yt
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near optimum moisture content. Prior to fill placement, the subgrade should be carefully
prepared by removing all vegetation and topsoil and compacting to at least 95o/o of the maximum
standard Proctor density. The fill should be benched into slopes that exceed 20o/o grade.
Permanent unretained cut and fiIl slopes should be graded at2hoizontal to I vertical or flatter
and protected against erosion by revegetation or other means. This office should review site
grading plans for the project prior to construction.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the structure has been completed:
1) lnundation 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 95o/o 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 6 inches in the first l0 feet in unpaved areas and a minimum slope of 2/z
inches in the first 10 feet in paved areas.
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 5
feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this areaat 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 exploratoryborings drilled excavated 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
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(MOBC) developing in the future. If the client is concemed 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 pu{poses. 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 veriff 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,
Ktlrtr*c" & Assqw.gm$*s, .Enn*.
Shane J. Robat, P.E.
Project Manager
Reviewed by:
Steven L. Pawlak,
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19-7-171 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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FILK GRAVEL, SILTY, SANDY, CLAYEY, BROWN, MEDIUM DENSE, MOIST.
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NOTF"S"-
1. THE EXPLORATORY FORINGS WERE DRILLED ON MARCH 20, 2019 WITH A 4-INCH DIAMETERCONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACINGFROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOI.ATION BETWEENCONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATEONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THEAPPRoXIMATE BoUNDARIES BETwEEN MATERTAL TypEs AND THE TRANStrroNs uli "er
cnaouaL.
6' GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
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7, LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTV O +ZZ);
-2Qo= PERCENTAGE PASSTNG NO. 200 SIEVE (ASTM D 1i4o).
19-7 -17 1 Kumar & Associates LEGEND AND NOTES Fig. 5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.1$7.171
SOILWPE
Slightly Silty Sandy Gravel
Slightly Silty Sandy Gravel
UI€ONFNED
colrPREsslvE
STRENGTH
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PIASTIC
INDEX
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loal
1 1
PERCENT
PASSING NO.
2{Xt SIEVE
I 0
NATURAL
DRY
DENS]TY
GRAVEL SAND
&t (%)
39
33
50
57
NATURAL
IiIOISTURE
COI{TENT
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SAIIPLE
DEPIII
{ft}
2Yz and 5
combined
2% and5
combined
BORING
1
2