HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(t i;#l[',ffifË:rnriiiå*"'
An Employcc Orrr.tcd Compony
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 Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 45, SPRING RIDGE RESERVE
HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO.22-7-787
JAI\UARY 19,2023
PREPARED FOR:
MIKE RICE
126 COUNTY ROAD 150
GLENWOOD SPRTNGS, COLORADO 81601
iessicarice@remax.net
TABLE OF CONTENTS
PROPOSED CONSTRUCTION I
FIELD EXPLORATION ...............- I -
SITE CONDITIONS
SUBSURFACE CONDITIONS
DESIGN RECOMMENDATIONS
FOLINDATIONS
FOTINDATION AND RETAINING \MALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRATNAGE
LIMTTATIONS......
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 through 6 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & A¡¡oclatel, lnc. o ProJect No. 22-7-787
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 45, Spring Ridge Reserve, Hidden Valley Drive, 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 agreement for geotechnical
engineering services to Mike Rice dated December 23,2022.
A freld exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock obtained during
the fîeld 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
Plans for the proposed residence were conceptual at the time of our field exploration. The
proposed residence will likely be a one- or two-story structure with attached garage possibly over
a lower basement level. Ground floors could be structural over crawlspace or slab-on-grade.
Grading for the structure is assumed to be relatively minor with cut depths between about 2 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 subject site was vacant at the time of our field exploration and there was approximately
6 inches of snow cover. The ground surface was sloping down to the north at a grade of about
15 percent. Vegetation consists of grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on December 29,2022. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
Kumar & A¡¡ociater, lnc. @ ProJect No. 22-7-787
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The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. Thc borings wcre logged by a representative of I(umar &
Associates, Inc.
Samples of the subsoils were taken with a.2-inch I.D. spoon sampler. The sampler was clriven
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 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.
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SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about Yz foot of topsoil overlying stiff to very stiff, sandy clay down to
between 13 and l8 feet deep. Below the clay in Boring l, hard, sandstone bedrock was
encountered to the boring depth of l6 feet. Below the clay soil in Boring 2, the soils consisted
of medium dense, silty sand down to 29 feetwhere hard sandstone bedrock was encountered to
the boring depth of 3l feet. Drilling in the hard/cemented bedrock with auger equipment was
difficult and drilling refusal was encountered at a depth of l6 feet in Boring l.
Laboral.ory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand grain size gradation analyses. Results of swell-
consolidation testing performed on relatively undisturbed drive samples of the clay soils,
presented on Figures 4 through 6, indicate low to moderate compressibility under conditions of
loading and wetting. The laboratory testing is summarized in Table L
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed constructiono we recommend the building be t'ounded with spread tbotings bearing
on the natural soils or bedrock material.
The design and construction criteria presented helow shor¡ld he ohserved for a s¡rearJ frroting
foundation system.
Kumar & Aæoclatel, lnc. o ProJect No, 22-7-787
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l) Footings placed on natural sandy clay soils should be designed for an allowable
bearing pressure of 1,500 psf. Based on experience, we expect initial settlement
2)
of footings designed and constructed as discussed in this section will be about
I inch or less. Additionalpost construction settlement could occur if the bearing
soils become wet. The magnitude of additional settlement would depend on the
depth and extent of wetting but could be on the order of I to l% inches.
The footings should have a minimum width of 18 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 least 36 inches below exterior grade is typically used in this
area.
Continuous foundation walls should be well reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12fieet.
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.
Topsoil and any loose disturbed soils should be removed and the footing bearing
level extended down to the relatively dense natural soils. The exposed soils in
footing area should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
3)
4)
s)
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. Cantilevered retaining structures which are separate from the residence 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 45 pcf for backfill consisting of the on-site 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
6)
Kumar & A¡¡oclater, lnc. o ProJect No, 22-7-787
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increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic prossure buildup behind rvolls. Backfill should not
contain topsoil, organics or rock larger than about 6 inches.
Backfill should be placed in uniform lifts and least90o/o of the maximum
standard Proctor density at a moisture content slightly above optimum. Backflrll placed in
pavement and walkway areas should be compacted to at leastg5Yo 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.
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 calculatcd
based on a coefficient of friction of 0.40. Passive pressure of compacted backfill against the
sidesofthefootingscanbecalculatedusinganequivalentnuioffiiFo'pcf.The
coetlicient of fþiction 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 compacted to at least 95Yo of the
maximum standard Proctor density at a moisture content near optimum.
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 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 lcss Lhan296 passing the Nr:. 200 sieve.
All fill materials for support of Íloor slabs shoulcl be compacted to at leastg5%o 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.
Kumar & As¡oclates, lnc. o Prdect No. 22.7-787
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UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow or clay soils are present 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 constructiono 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%o passing the No. 200 sieve, less than 50%o passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence 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 90o/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 l0 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 irrigation should be located at least
5 feet from foundation walls. Consideration should be given to the use of
xeriscape to limit potential wetting of soils below the foundation caused by
irrigation.
Kumar & A¡aoclates, lnc, o ProJect No, 22-7-787
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LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this tirne. Wc 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 consulterl. Our findings inclucle 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. Vy'e 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$r 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 &
James H. Parsons,
Reviewed by:
¡'I
Daniel E. Hardin, P.E.
JHP/kac
Kumar & Associates, lnc.oì)Project No. 22-7.787
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APPROXIMATE SCALE-FEET
22-7 -787 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
0 0
26/12
43/12
WC=8.2
DD=94
5 22/12
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WC=17.8
DD= 1 08
-2OO=77
20 2015/12
25 25
30 3050/3
35 35
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T 22-7 -787 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
TOPSOIL; CLAY, SANDY, SILTY, ORGANICS, FIRM, MOIST, DARK BROWN
CLAY (CL)¡ SANDY, SILTY, STIFF TO VERY STIFF, SLIGHTLY MOIST, RED.
SAND (SM)i SILTY, MEDIUM DENSE, MOIST, RED.
SANDSToNE (ss); uanooN FoRMATIoN, HARD, SLIGHTLY MolsT, RED.
DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE.
^ê,.ı DRIVE SAMPLE BLOW COUNT. INDICATES THAT 26 BLOWS OF A 140-POUND HAMMERzo/ ta FALLTNG 30 rNcHEs wERE REQUIRED To DRtvE THE SAMPLER 12 lNcHES.
f nnncrrcnL AUGER REFUsAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 29, 2022 WIÍH 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 PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF
THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS 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) (ISTV D2216);
-2AO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
Fig. 3LEGEND AND NOTES22-7 -787 Kumar & Associates
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SAMPLE OF; Sondy Sllty Cloy
FROM:Boringl@5'
WC = 10.8 %, DD = 111 pcf
tl& tcd ruÈ opDly onty b baeñplcr 16#. tu t rting Époi.holl nd b Épdæ.d, .xc.Þt lñ
f0il. rnh@t thc rdtbn aÞÞddl of
Kumor ond A¡æItu, læ. Sr.il
CoMllddloñ bllno ærlom.d In
ocærdanc. rtrh m D-S{6.
NO MOVEMENT UPON
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SAMPLE OF: Sondy Silty Cloy
FROM:Boring2(9^2.5'
WC = 8.2 o/", DD = 94 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
lhdr tút É¡ultr opÞY o^t to tha
6mÞl6r lcdrd. Ih. büng rôport
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22-7 -787 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
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SAMPLE OF: Sondy Silty Cloy
FROM: Boring 2 G! 10'
WC = 9.8 %, DD = 107 pcf
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rm taú ruE opÞ¡y oñty þ ùaEmpl.! tcrù.d. th b!ünq ruærl
rholl ñot b. ßpdæd. .lc.pl lnfuÍ, rnhd th. rltt n opFùol ot[uñôr od turælot .. læ. Sr.ll
Condldotlon Lltlnq Fñôm.d lnodncâ rilh m D-{96-
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UNDER CONSTANT PRESSURE
DUE TO WETÏING
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22-7 -787 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 6
lcrtl(unw&AssociG, lno.'Geotechnical and Materials Engineersand Environmental ScientistsTABLE 1SUMMARY OF LABORATORY TEST RESULTSSandy Silty ClaySandy Silty ClaySandy Silty ClaySandy Silty ClaySandy Silty ClaySandy Silty ClaySOIL TYPElpsflUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEX(o/"1ATTERBERG LIMITSPlolLISUID LIMITIIt)77PERCENTPASSING NO,2()(l SIEVESANDlYolGRADATIONf/,1GRAVEL108locflNATURALDRYDENS]tY11110294I0It078.210.s9.817.8lololNATURALMOISTURECONTENT10.813.7{ftìDEPTH50IZYz501l52SAMPLE LOCATIONBORINGINo.22-7-787