HomeMy WebLinkAboutSubsoil Study for Foundation Design - Proposed Cabin - 04.19.2022rcrf iiçl['ff:ifß:i;niTiå *' "
An Employec Owned Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 94s-84s4
email: kaglenwood@kumarusa.com
wwwkumarusa.com
Ofüce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colo¡ado
April 19,2022
4ET,LLC
c/o John Kuersten
PO Box 1530
13 Powerline Road
Rifle, CO 81650
i ohn@kuerstenconstruction. com
REGEIVED
jt,h¡ l] I lrl?Î
GARFIELD COUNTY
COMM UNITY DEVELOPMEì{T
Project No.22-7-164
Subject: Subsoil Study for Foundation Design, Proposed Cabin, V/est of 1777 County
Road 24l,East Elk Creek Road, 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 proposal for geotechnical
engineering services to 4 ET, LLC dated February 3,2022. The data obtained and our
recoÍlmendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed cabin will be a two-story wood-framed structure located
in the general vicinity of the borings shown on Figure 1. Ground floor will be slab-on-grade or
structural over crawlspace. Cut depths are expected to range between about 3 to 5 feet.
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 recolnmendations presented in this report.
Site Conditions: The project site is currently vacant. There is an existing two-track driveway
that accesses the proposed building site. Topography at the site is hilltop with variable slopes
generally down to the northwest and southeast. Vegetation at the site consists of native grass and
weeds with scattered sagebrush, scrub oak, and juniper trees.
Fietd Exploration: The field exploration for the project was conducted on April 4,2022. 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-45B 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 subsurface materials at various depths with blows from a 140-pound
-2-
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.
Subsurface Conditions: Graphic logs of the subsurface conditions ençountered at the site are
shown on Figure 2. The subsoils consist of about I to 2 feet of silty sand with gravel overlying
siltstone/sandstone bedrock of the Maroon Formation. Drilling in the bedrock with auger
equipment was difficult due to the hardncss and drilling refusal was encountered in thc deposit at
depths of 16 and 6 feet in Borings I and2, respectively.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and percent finer than sand size gradation anaþses. The laboratory testing is
sr¡mmarizecl in Table 1.
No free water was encountered in the borings at the time of drilling and the subsurface materials
were slightly moist to moist.
Foundation Recommendations: Considering the subsurface conditions encountered in the
exploratory borings and the nafure of the proposed construction, we recommend spread footings
placed on the undisturbed natural bedrock designed for an allowable bearing pressure of
3,000 psf for support of the proposed cabin. Footings should be a minimum width of l6 inches
for continuous walls and2 feet for columns. Loose and disturbed soils and existing road fill
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level extended down to the undisturbed natural bedrock. 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 foundation walls should be reinforced top and bottom to span local anomalies such
as by assuming an unsupported length of at least l0 feet. Foundation walls acting as retaining
structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 45 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils and bedrock, exclusive of topsoil, are suitable to support
lightly loaded slab-on-grade construction. To reduce the effects of some differcntial 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.
Kumar & Associates, lnc. @ Project No. 22-7-164
-3-
This material should consist of minus 2-inch aggregate with less than50o/o passing the No. 4
sieve and less than 2o/opassingthe No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at teast95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the arca and where bedrock is shallow 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, crawlspace and basement areas, be protected from wetting and hydrostatic
prossure 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 Io/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Yopassingthe 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 and covered
with filter fabric such as Mirafi 140N.
Surface I)rainage: The following drainage precautions should be observed during construction
and maintained at all times after the cabin 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 90Yo of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
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
3 inches in the first l0 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practioes in this area atlhis time, We make no warranty either
express or implied. The conclusions and recommendations submitted in this report are based
Kumar & Associates, lnc. @ Project No. 22-7-164
-4-
upon the data obtained from the exploratory borings drilled at the locations indicated on Figure I
and to the depths shown on Figure 2,theproposed 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 of the subsurface conditions identified at the
exploratory borings and variations in the subsurface conditions may not become evident until
exoavation is performed. If conditions encountered during construction appear diff-erent from
those described in this report, we should be notified at once so 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 verifo that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations preseriled herein. We recornmend 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 further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, Inc.
Robert L. Duran, P.E.
Reviewed by:
l.fuL
* Steven L. Pawlak, P.E.
RLD/kac
attachments Figure 1 - Location of Exploratory Borings
Figure 2 - Logs of Exploratory Borings
Figure 3 - Legend and Notes
Table I - Summary of Laboratory Test Results
Kumar & Associates, lnc. o Project No. 22.7-164
E
I
TO 1777 COUNTY
ROAD 241
ó eonrxo t
DIRT
DRIVEWAY
I
I
15 50
APPROXIMATE SCALE-FEET
Fig. 1Kumar & Associates LOCATION OF EXPLORATORY BORINGS22-7 -1 64
I
E
=
I
BORING 1
E1.6156'BORING 2
EL. 61 56'
0 0
37 /6, sO/4.5
WC=3.6
DD=122
44/12
tNC=7.7
DD= 1 30
-200=54
5 550/6
WC=2.5
DD=127
50/2.5
t-LJ
lJJtL
IIF(L
L¡lô
10 10
t-
UJ
UJ
l!
IIF(L
ulo
50/3
'15 1550/ 1
20 20
22-7 -164 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
I
e
I
LEGEND
SAND (SM) STLTY TO VERY S|LTY, WITH GRAVEL, LOOSE TO MEDIUM DENSE,
MOIST, RED.
W
WEATHERED SILTSTONE/SANDSTONE, MEDIUM HARD, MOIST, RED, SLIGHTLY
CALCAREOUS.
SANDSTONE/SILTSTONE, VERY HARD, SLIGHTLY MOIST, RED, CEMENTED.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
I DRTVE SAMpLE, 1 S/B-|NCH t.D. SPLIT SPOON STANDARD PENETRATIoN TEST
44/ 12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 44 BLOWS OF A 14o-POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
PRACTICAL AUGER REFUSAL.I
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 4, 2022 VIITH 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.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING 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 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 (PCI) (ASTV D2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140).
LEGEND AND NOTES Fig. 522-7 -164 Kumar & Associates
lGrliiffififfifffii;i'iy;-'"TABLE ISUMMARY OF LABORATORY TEST RESULTS7.7130LIQUID LIMITWeathered SiltstoneSOIL TYPEI2BORIIG1DEPT}I(o/"1GRAVEL(v'lSANB5452%2.53.6t27122Siltstone/SandstoneSiltstone/SandstoneNATURATMOISTUREcot{lENTNATURALDRYDENSIWPERCENTPASSING NO.200 stnrEPLASTICINDEXUNCONFINEDCOMPRESSIVESTREi¡GTHNo.22.7-164