HomeMy WebLinkAboutSubsoil Studyl(fÄm,m:m'ff**"5020 County Road 154
Glenwood Springs, CO 8ló01
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.corTAn Emdsycc Orned Compony
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
!tjl,j i 4 liii'i
GARFIELD COI.JNTY
COMMUNITY DEVELOPMENT
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT SD.T4, ASPEN GLEN
SUNDANCE TRAIL
GARFIELD COUNTY, COLORADO
PROJECT NO.21-7-902
JANUARY 24,2022
PREPARED FOR:
JORDAI\ ARCHITECTURE
ATTN: BRAD JORDAN
P.O. BOX 1031
GLENWOOD SPRINGS, COLORADO 81602
brad i ordan arch itect@email.com
TABLE OF CONTENTS
PTIRPOSE AND SCOPE OF STUDY.....
PROPOSED CONSTRUCTION
STTE CONDTTIONS...........
SUBSIDENCE POTENTIAL..
FIELD EXPLORATION
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 . LOGS OF EXPLORATORY BORINGS
FIGURE 3 . LEGEND AND NOTES
FIGURE 4. GRADATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
I
I
.,......,..........- 2 -
SUBSURFACE CONDITIONS ...2-
FOLTNDATION BEARING CONDITIONS.......¿!....i.... ......- 3 -
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...
LIMITATIONS
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J
4
4
5
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Kum¡r & A¡soclatæ, lnc. o Pmþc.t llo. 21.7.92
PURPOSE AI\D SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residçnce to be located on
Lot SD-14, Aspen Glen, Sundance Trail, Garfield County, Colorado. The project site is shown
on Figure l. The pu{pose 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 23,202I.
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 fîeld 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 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 4 feet. We assume relatively light
foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change signíficantly 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. The ground surface was gently
sloping down to the west. Outside the east properly line, the ground surface slopes down to a dry
drainage ditch. Vegetation consists of grass and weeds.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision.
These rocks are a sequence of gypsiferous shale, fîne-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 ofthe lot. Dissolution of the
Kumar &A¡sociatæ, lnc. o Projec't No.2l-7.902
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gypsum under certain conditions can cause sinkholes to develop and can produce areas of
localized subsidence. During 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 350 feet northwest of Lot SD- 14, under the pond to the northwest. These
sinkholes appear sirnilar to others associated with the Eagle Valley Evaporite in areas of the
middle to lower Roarlng 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-14 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 field exploration for the project was conducted on December 8,2021. 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, lnc.
Samples of the subsoils were taken with a l%-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-I586. 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 va.h¡es 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.
SUBSURF'ACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountered, below about Yzfoot of topsoil, consist of gravelly fill to be¡¡¡een2 and
4 feet deep overlying dense, silty sandy gravel with cobbles and probable boulders to the
maximum explored depth of 8 feet. Drilling in ths dense granular soils with auger equipment
was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit.
Kumar&Aa¡ociale¡, lnc. o Pmject trlo.2l.7.90úl
-J-
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 f -inch fraction) of the coarse granular subsoils are shown on Figure 4. The
laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
FOUI\IDATION BEARING CONDITIONS
The upper fill soils are undocumented and not suitable for support of the proposed residence.
The natural sandy gravel soils possess moderate bearing capacity and typically low settlement
potential. At assumed excavation depths we expect the subgrade will expose the natural sandy
gravel soils. Shallow excavation areas or slab-on-grade areas may expose the upper flrll soils.
Areas that expose filI soils should be deepened to expose natural granular soils. The sub-
excavated depth can be backfilled with the onsite soils excluding topsoil, debris or rocks larger
than 6 inches. Spread footings should be feasible for foundation support of the residence with a
low risk of settlement.
DESIGN RECOMMENDATIONS
FOLINDATIONS
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.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils 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.
2) The footings should have a minimum width of 16 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.
Kumar & Asgoclatê¡, lnc. o PrcJeot No. 21-7-902 '
4
4)Continuous foundation walls should be reinforoed 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 designecl to resist a
latcral earth pressure çonesponding to an equivalent fluid unit weight of at least
45 pcf for backfill consists of the on-site granular soils.
All existing fill, topsoil 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.
FLOOR SLABS
The natural on-site coarse granular 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.
'l'his material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4
sieve and less than 2% passing the No.200 sieve.
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 of vegetation, topsoil and oversized rock.
IINDERDRAIN SYSTEM
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 precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. 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 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
5)
6)
Kumar & As¡ocht6ç, lnc. o Ptoþct ilo.21-7.901
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a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2olo 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 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:
t) 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 95o/o oîthe maximum standard Proctor density in pavement and sl4b areas
and to at least 90a/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 6 inches in the fïrst l0 feet in unpaved areas and a minimum slope of
3 inches in the frrst 10 feçt in paved 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 infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of ali
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 arcaat 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 borings drilled at the locations indicated on Figure l, 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 consulted. Our findings include interpolation and extrapolation ofthe
subsurface conditions identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
Kumar & Assoclates, lnc. o Prciect No.21.7-902
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drring constnlcfion 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 oru client fbr design purposes. We are not
rosponsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during constuction to review and
monitor the implement¿tion of our recommendations, and to veriff that the recomme,ndations
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 & Associateso fnc,
James H. Parsons, P.E.
Rwiewedby:
Steven L. Pawlak, P.E.
JHP/kac
Kumar & Associates, lnc. o Project t{o.2l-7-902
20 0 40
APPROXIMATE SCALE-FEET
21 -7 -902 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1 BORING 2
0 0
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33/6,50/4.s
32/6, sO/s
WC=1.4
*4=38
-200=1 5
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5 538/6, 5o/5
WC=1.5
+4=61
-2OO=7
84/ 12
10 10
21-7-902 Kumar & Associates LOGS OF TXPLORATORY BORINGS Fis. 2
e
LEGEND
TOPSOIL: SAND AND SILT, GRAVELLY, CLAYEY, SCATTERED COBBLES, ORGANICS.
FIRM, MOIST, BROWN.
FILL¡ GRAVEL AND SAND, SILTY, CLAYEY, COBBLY, MEDIUM DENSE, SLIGHTLY
MOIST, LIGHT BROWN AND GRAY.
GRAVEL (0U-Oe): SANDY, CoBBLES, SLIGHTLY S|LTY T0 SILTY, PROBABLE SMALL
BOULDERS, DENSE, SLIGHTLY MOIST, GRAY AND TAN.
¡
DRTVE SAMPLE, 1 3/1-|NCH r.D. SPL|T SPOON STANDARD PENETRATTON TEST
RA/12 DRIVE SAMPLE BLow CCIUNT. INDICATES THAT 84 BLOWS OF A |4O-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I PRACTICAL AUGER REFUSAL.
NOTEg
1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 8, 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 ELIVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS ARE PLOTTED TO ÐEPTH.
4. THE EXPLORATORY BORING LOCAÏIONS SHOULD BE CONSIDERED ACCURATE ONLY 10 THE
DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MAÏERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTTRED IN THE BORINGS AT THE TIME OF DRILLING
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140).
21 -7 -902 Kumar & Associates LTGTND AND NOTES Fig. 3
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SAMPLE OF: Sllghtly Sllty Sondy Grovel
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PLASTICITY INDEX
SILT AT,ID CI-AY 7 X
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SAilPLE OF: Sllty Sond ond Grovel (Flll)
17%
PLASIICIW INDEX
SILT AND CLAY 15 %
FROM:BorlngZe2,5'
Th.æ tott ruulls qpply only to lhorompls whlch wrn læl.d. lh.Lr{lng ruporl rholl not b. nprcduc.d.
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Sl.vó onolyrls ta¡llng l! plrfoñ.d ln
oôoordqnc. wfth -ASTM Dß91J, ASTM 07924
ASTI¡ C15ô ondlor ASTM Dll4{1.
I{YDROYEIER ANALYSIS SIEVE ANALYSIS
z4 HRS 7 HnSg !r¡ r! !¡f, mlN dtx t!tN a:
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SAND GRAVEL
FINE MEDIUM FINE COARSE
HYDROMET€R ANALYSIS SIEVE ANALYSIS
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FINE MEDIUM COARSE FINE COARSE
21 -7 -902 Kumar & Associates GRADATION TEST RTSULTS Fis. 4
lcrtHffi[mmffü-"'TABLE ISUITIMARY OF LABORATORY TEST RESULTS212IBORII{G2y,5rfrlDEP'IH1.415f/,1NATURATMOlsNNECONTENTfûcÍìT{ATURAI-DRYDENSNW386IlY"lGRAVEL4732SAND(f/"1GRADATIONI57PÊRCENTPASSIiIG NO,2m sEvELIQI'IDLilfTI%lt%)PLASTICIt{ÐEXATTERBERG LJilNSloeflUNCONFINEDCOMPRESSIVESTREiIGTHSilty Sand and Gravel (Fill)Slightly Silty Sandy GravelSOILTYPE