HomeMy WebLinkAboutSubsoil Studytcrt lmrr&lÉsocffi¡,lnc.@
Geotechnical and Materials Engineen
and Environmental Scientisb
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-79t8
fax: (970) 945-8454
email : kaglenwood@kumarusacom
www.kumarusa.cothAn tsnploycc ot*nccl Conrpony
Office Locations: Denvø (tlQ), Puker, Colorado Springs, Fort Collins, Glenwood Springs, and Surnmit County, Colorado
RECEIVED
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GARFIELD COUNTY
COUtrtUHtrV DEv ELOPMENT
SUBSOIL STUDY
F'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT SD-15, ASPEN GLEN
STJNDA¡ICE TRAIL
GARFIELD COUNTY, COLORADO
PROJECT NO.21-7-903
JANUARY 25,2022
PREPARED FOR:
JORDAN ARCHITECTURE
ATTN: BRAD JORDAN
P.O. BOX 1031
GLEN\ryOOD SPRINGS, COLORADO 81602
brad i ordanarch itect@email.com
TABLE OF CONTENTS
PIJRPOSE AND SCOPE OF STUDY ....- I -
PROPOSED CONSTRUCTION ....... I .
SITE CONDITIONS I
SUBSIDENCE POTENTIAL
FIELD EXPLORATION ...............
SUBSURFACE CONDITIONS ....
FOTINDATION BEARING CONDITIONS
FOIINDATIONS
FLOOR SLABS..
2-
2-
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..-4-
LIMITATIONS.5
FIGURE 1 . LOCATION OF EXPLORATORY BORINGS
FIGURE 2 . LOGS OF ÐOLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL.CONSOLIDATION TEST RESULTS
FIGURE 5 . GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & A¡soclater, lnc. o Prcþct No. 21-7-903
PURPOSE AIID SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot SD-15, Aspen Glen, Sundance Trail, Garfield County, Colorado. The project site is shown
on Figure l. 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 Jordan Architecture dated November 23,2021.
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 analyzedto 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 \ryere conceptual at the time of our study. The proposed
residence will likely be a two-story structure with attached garage. 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 2to 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 subject site was vacant and covered with a few inches of snow at the time of our field
exploration. The ground surface was undulating with a general slope down to the southwest. A
dry drainage ditch is at the rear of the lot. Vegetation consists of grass and weeds with scattered
bushes.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
Kumar & A¡eociatet, lnc. o Proþct No.2f-7-9lli¡
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massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits
associated with the Eagle Valley Evaporite underlie portions of thc lot. Dissolution of thc
Bypsum undcr ccrLain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. Durìng previous work in the area, several sinkholes were observed
scattered throughout Aspen Glen, mainly east of the Roaring Fork River. A small sinkhole was
mapped about 425 feet northwest of Lot SD-15, under the pond to the riorthwest. These
sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the
middle to lower Roaring Fork River valley.
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 Lot SD-I5 throughout the service life of the proposed
residence, 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 fïeld exploration for the project was conducted on December 10,2021. 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 l%-inch and 2-inch I.D. spoon samplers. The samplers
were driven into the subsoils at various depths witì blows from a 140-pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-I586.
The penetration resistance values aÍe an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resist¿nce 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 about t/zfootof topsoil, consist of about 2t/zto3Yzfeetof very stiff,
sandy clay overlying dense, sandy gravel with cobbles and probable boulders down to thc
Kumar & A¡¡oclate¡, lnc. o Projecf l{o.21.?.90i1
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maximum explored depth of I feet. Drilling in the dense grcnular soils with auger equipment
was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from thç borings included natural moisture
content and density and gradation analyses. Results of swell-consolidation testing performed on
a relatively undisturbed drive sample of the sandy clay, presented on Figure 4, indicate low to
moderate compressibility under conditions of loading and wetting. Results of gradation analyses
performed on a small diameter drive sarnple (minus lYz-inch fraction) of the coarse granular
subsoils are shown on Figure 5. 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
slightlv moist'
FouNDATIoN BEARTN. coNDITIoNS
The upper sandy clay soils possess low bearing capacity and low to moderate settlement
potential. The natural sandy gravel soils possess moderate bearing capacþ and typically low
settlement potential. At assumed excavation depths we expect the subgrade will expose the
sandy gravel soils. Shallow excavation areas or slab-on-grade areas may expose the upper sandy
clay soils. Footing areas that expose clay soils should be deepened to expose natural granular
soils. The sub-excavated depth can be backfilled with the onsite granular soils excluding rocks
larger than 6 inches. Spread footings placed on natural granular soils or compacted structural fill
should be feasible for foundation support of the residence with a low risk of settlement.
DESIGN RECOMMENDATIONS
FOUNDATTONS
Considering the subsurface condítions 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 or structural fill compacted to at least 98% of standard Proctor
density.
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 or structural fïll should
be designed for an allowable bearing pressure of 3,000 psf. Based on experience,
we expect settlement of footings designed and constructed as discussed in this
section will be about I inch or less.
Kumar & At¡oclatec, lnc. o Prclec{ No.2ll:903
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3)
The fbotings should havç a minimum width of l6 inches for continuous walls and
2 tbet t'ot 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 reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure coriesponding to an equivalent fluid unit weight of at least
45 pcf for backfill consisting of the on-site granular soils.
Topsoil, sandy clay soils and any loose disturbed soils should be removed and the
footing bearing level extended down to the relatively dense natural granular 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.
4)
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 less than2Yo passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fïll can consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYS'I'ËM
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 precipiøtion or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
2)
5)
6)
Kumar&A¡roclates, lnc. o Proþct 11o.21.7.903
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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 levsl of
excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum l%oto
a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2Yo passing the No. 200 sieve, less than 50oá 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:
l) 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 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 6 inches in the flrrst l0 feet in unpaved areas and a minimum slope of
3 inches in the first l0 feet in paved areas. Free-drainìng 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
backftll.
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 area at this time. TVe 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
Kumar &Asoociates, lnc, @ Prcject l,lo.2l-7-903
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presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concerned about MOBC, then a protbssional in this special field of
practice should be consultecl, Our findings inclucle interpolation and extrapolation of the
subsurface conditions identified at the exploratory borings and variations in the suhsurface
conditions may not become evident until excavation is performed. If conclitions encountered
during construction appear different from those described in this re,port, we should be notified so
that re-evaluation of the recommendations may be made.
Ïris report has been pre,pared for the exclusive use by our client for design purposes. We are not
responsiblc for tcchnical.interpretations by others of our information. As the project evolves, rve
should provide continued consultation and field services during construction to revierv and
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional anaþsis '
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.
James H. Parsons, P.E.
Reviewed by:
**/-
Steven L. Pawlak, P.E.
JHPlkac
Kumar& Associatea, lnc. @ Project No. 21-7-gA?
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APPROXIMATE SCALE_FEET
21 -7 -903 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
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WC=8.2
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WC=1.0
+4=51
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10 10
21 -7 -903 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
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TOPSOIL: CLAY AND SAND, SILTY, SCATTERED GRAVEL, ORGANICS, FIRM, MOIST,
DARK BROWN.
CLAY (CL): VERY SANDY, SCATTERED GRAVEL WITH DEPTH, SLIGHTLY
CALCAREOUS, VERY STIFF, SLIGHTLY MOIST ÏO MOIST, LIGHT BROWN, SLIGHTLY
POROUS.
GRAVEL (GM-GP): SANDY, COBBLES, SLIGHTLY SILTY, PROBABLI BOULDERS,
DENSE, SLIGHTLY MOISÏ, BROWN AND GRAY.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
i DR|VE SAMPLE, 1 S/9-|NCH r.D. SPLIT SPOON STANDARD PENETRATION TEST.
,'^/,tt DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 BLOWS OF A 140-POUND HAMMER'-l .- FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 'I2 INCHES.
I enlcrrcal AUGER REFUSAL.
NOTES
THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 10, 2021 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 PLAN PROVIDED.
3. TIIE ELËVATIONS OF THT EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
+. THE EXPLORATORY BORING LOCATIONS SI{OULD 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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
1
Fig. 3LTGEND AND NOTES21 -7 -903 Kumar & Associates
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SAMPLE 0F: Sondy Cloy
FROM:Boring2e.2.5'
tttC = 7.2 rt, DD.= 99 bcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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21-7-9A3 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS Fig. 4
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PÀRTICLES IN
1.18 4.76 9.9 l9 200
DIAMETER OF
CLAY TO SILT CO6BLES
GRAVEL 51 % SAND
LIQUID UMIÎ
SAMPLE OF: Very Sondy Sllty Grovel
37%
PLASTICIÏY INDEX
SILT AND CI.AY 12 %
FROM:Boringl05'
fh.!o lÉl r.sulli qpply only tô lhr
eqmplG vhlch won l6lod. Th€
losllng rlparl sholl not b. r.prcduc.d,
excepl ln fqll, wllhoul lhc wrltlonqpprcvql oî Ksmor & A3Eoclqbt, lnc.
Slava qndlysl! t.dlng l¡ p.rtomld lnqôcordonca vllh ASfl, D6913, ASTM D7928,
ASll¡ C156 qnd/or ASÍM Dll,to.
HYDROMETER ANALYSIS SIEVE ANALYSIS
ÎT'E READINGS
14 HRS 7 HRS
u.s. SÍANDAiD sERtES
a4ô ¡ó ¡tô ¡tß
ctÊAR souARE oPEl{tNos
tlàr a/^. t t /r- ¡.
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SAND GRAVEL
FINE I veoruv lcornsr FINE COARSE
21 -7 -s03 Kumar & Associates GRADATION TEST RESULTS Fis. 5
TABLE ISUMMARY OF LABORATORY TEST RESULTS2IBORII{G2Y25zVz{ft}DEPTH7.2I08.2t%¡I{ATURALHOISTURECü{TEñfT9993I{ANNALDRYDEI{S¡TY{nôll51(vùGRAVEL37P/"1SA¡ÐGRADATþI{t277PERCEI{fPASStilG NO.200 sEvELKIUTD Uün(o/øl{%}ruASilCliDÊ(ATTERBERG LffiTSfp6llt¡r¡coNFlr¡EDc0¡tPREssirvESTRENGTHSandy ClayVery Sandy Silty GravelSandy ClaySOILTYPENo.2f