HomeMy WebLinkAboutSubsoil Studyl(lrt I(umar & Associates, lnc. 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 91601
and Environmental scientists phone: (970) 945_7ggg
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
An Employcc Owncd Compony www.kumarusa.com
Offìce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
June22,2020
Sunrise Company
Attn: Teddy Farrell
0115 Boomerang Road, Suite 52018
Aspen, Colorado 81611
tfarre I I @sunri seco. co m
Subject:
Project No.20-7-331
Subsoil Study for Foundation Design, Proposed Residence, LotE-12, Aspen
Equestrian Estates, 48 Equestrian Way, Garfield County, Colorado
Gentlemen
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to Sunrise Company dated June 9,2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Development plans for the lot were not available at the time of our
study and our findings will be considered in the purchase of the lot. We assume the proposed
residence will be a one or two-story structure with an attached garage located within the building
envelope shown on Figure 1. Ground floor could be structural over crawlspace or slab-on-grade.
Cut depths are expected to range between about 2 to 3 feef. Foundation loadings for this type of
construction are assumed to be relatively light and typical of the proposed type of construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The lot was vacant at the time of our site visit. The lot is flat, slopes slightly
down to the south and is vegetated with grass and weeds. A marshy area is located directly north
of the lot. Eagle Valley Evaporite bedrock is exposed on the valley hillsides to the north and
south.
Subsidence Potential: Aspen Equestrian Estates is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under
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certain conditions can cause sinkholes to develop and can produce areas oflocalized subsidence.
During previous work in the area, sinkholes were observed in this part of the Roaring Fork River
valley but not in Aspen Equestrian Estates. Sinkholes or indications of surface subsidence or
subsurface voids were not observed in the immediate area of the subject lot nor encountered in
the exploratory pits dug on the lot. Based on our present knowledge of the site, it cannot be said
for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot
E-l2 throughout the service life expectancy of the residence is low and similar to other lots in the
area but the owner should be aware of the potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about one foot of topsoil, consist of
medium stiff, sandy silty clay to a depth of about 5% feet. Relatively dense, slightly silty sandy
gravel and cobbles was encountered below the clay to the maximum explored depth of 6 feet.
Results of swell-consolidation testing performed on relatively undisturbed samples of sandy silty
clay, presented on Figure 3, indicate low compressibility under existing moisture conditions and
light loading and moderate compressibility when wetted and subjected to increased loading.
Free water was observed in the pits at a depth of about 4Yz feet at the time of excavation. The
upper soils were very moist to wet with depth.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural clay soil below the topsoil designed for an allowable soil
bearing pres sure of I for ofthe proposed residence. F ooting depth should be
kept shallow,around 2 to 3 feçLbelow ground qq4face to help avoid soft wet soils. Soft subgrade
soils could need localized stabilization such as with geogrid and around 12 inches of CDOT
Class 2 (minus 3-inch) base course. We should observe the bearing soils within the excavation
prior to forming for footings. The clay soils tend to compress when loaded and there could be
post-construction foundation settlement of around 1 inch. Footinss should be a minimum width
of 20 inches for continuous walls and2 feet for columns. The topsoil and loose disturbed soil
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level extended down to the undisturbed natural soils. Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection. Placement of
footings at least 36 inches below the exterior grade is typically used in this area. Continuous
Kumar & Associates, lnc.Project No. 20-7-331
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foundation walls should be heavily 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 alateral earth pressure based on an equivalent fluid
unit weight of at least 55 pcf for the on-site soil as backfill excluding organics and rock larger
than 6 inches.
Floor Slabs: Slab-on-recommended to avoid moisture associated with
is shallow. The natural on-site soil s, 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 should be beneath interior slabs
to facilitate drainagç. This material should consist of minus 2-inchaggregate with less than50Yo
passing the No. 4 sieve and less than2%o passing the No. 200 sreve
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 fill can consist of the
onsite soils devoid of vegetation, topsoil and oversized rock. High moisture clay soils could
require drying before placing as structural fill.
We recommend vapor retarders conform to at least the minimum of ASTM 81745
Class C floor types are more sensitive to water vapor transmission than others.
For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor
transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum
requirements of ASTM 81745 Class A material. The vapor retarder should be installed in
accordance with the manufacturers' recommendations and ASTM 81643.
Underdrain System: Free water was encountered during our exploration and it has been our
experience in the area that the groundwater level can rise during irrigation season. We
recommend below-grade construction, such as retaining walls and crawlspace areas, be protected
from wetting and hydrostatic pressure buildup by an underdrain system. The underdrain should
not be needed ifthe ground floors are slab-on-grade and elevated above the sunounding area.
The drains should consist of rigid perforated drainpipe placed in the bottom of the wall backflrll
surrounded above the invert level with free-draining granular material. The drain should be
Kumar & Associates, lnc.Project No. 20-7-331
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placed at each level of excavation and at least I foot below lowest adjacent finish grade and
sloped at a minimum %%o to a suitable gravity outlet or sump and pump. Free-draining granular
material used in the underdrain system should contain less than 2Yo 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 lYz feet deep.
Surface I)rainage: 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%o 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.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, finer graded soils to reduce surface water inf,rltration.
3) The ground surface sunounding 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 10 feet in unpaved areas and a minimum slope of
2Yzinches in the first l0 feet in pavement and walkway areas.
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 the building.
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 pits excavated at the locations indicated on Figure I
and to the depths shown on Figure 2, 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 flreld of practice should be consulted. Our
findings include interpolation and extrapolation of the subsurface conditions identified at the
exploratory pits and variations in the subsurface conditions may not become evident until
excavation is performed. If conditions encountered during construction appear different from
Kumar & Associates, lnc.Project No. 20-7-331
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those described in this report, we should be notified at once so re-evaluation of the
recommendations may be made.
This repof 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 fie1d 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.
If you have any questions or if we may be of filrther assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, fnc.
Steven L.
Reviewed by:
Daniel E. Hardin, P.E.
SLPlkac
Attachments: Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 * Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
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20-7 -331 Kumar & Associates LOCATION OF EXPLORATORY PITS 1Fig.
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PIT 1
EL. 100.5'
PIT 2
EL. 1 02.5'
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WC=25.9
DD=96
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5 5
10 10
TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, BROWN.
CLAY (CL); SILTY, SANDY, MEDIUM STIFF, VERY MOIST TO WET WITH DEPTH, BROWN, LOW
PLASTICITY.
SAND, GRAVEL AND COBBLES (CU-Op); SLIGHTLY SILTY, DENSE, WET, SROWN, ROUNDED
ROCK.
F
[:
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
- DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF EXCAVATION.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JUNE 10, 2020.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
THE BENCHMARK ON FIG. I.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUND WATER 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 D 2216):
DD = DRY DENSITY (PCt) (ISTU D 2216);
-2OO= PERCENTAGE PASSING NO. 200 SIEVE
UC = UNCONFINED COMPRESSIVE STRENGTH
(ASTM D r14o);
(psf) (ASTM D 21 66).
¡NC=21 .4
DD=98
-20Q=70
UC= 1 ,000
20-7 -331 Kumar & Associates LOGS OF' EXPLORATORY PITS Fig. 2
17, 2020 - l1:1&nLðtãävil=PN'I'r|1!¡Ëo(of-à(@ g3 ä-åag!=rO<oloi. €-Irrt¡ãflËV,øcoÐ2.frlcE=o;ñz.ÐÉc)r"lO12.-, u1ãi-{-tTA/\z,tCoNSoLTDATTON - SWELL (%)oIINI(r¡I5ooCoNSoLTDATTON - SWELL (%)olll¡À(xNÞTTEmITvr0Øc7rI:Ð>o<r5PT, rrlP=oo)Nf,-)q@g-=u!¡o-\J¿n<ll g.oÈoq€zo{?fî Fti<-.: fîz.z6) -{c1'oz.IIIII=-:í3ãi r..-É3o ç9.. t>- rdËrìee.o -: rãålÉree s Ii'gãç iãsäegsåiããqoı'r1q.;oat{ıÉtN)oI!I(^I^c30¡9oØØoo.0)o(t,tJl€rflT-r-IC)oz.UIOt-O-loz-.1rÌtU)-{nfnUIct--lU)=I(¡
l(t t iiffiimffffffi1':ifü-"'TABLE 1SUMMARY OF LABORATORY TEST RESULTSSandy Silty ClaySandy Silty ClaySOIL TYPEATTERBERG LIMITSLIOUID LIMITUNCONFINEDCOMPRESSIVESTRENGTHPLASTICINDEXSandy Silty Clay1,00070PERCENTPASSING NO.200 sIEVE98104GRADATIONNATURALDRYDENSITYSAND(%)GRAVEL(:/"121.418.6IololNATURALMOISÏURECONÏENT23v,lf0DEPTH25.93Y,96I2SAMPLE LOCATIONPITNo.20.7-331