HomeMy WebLinkAboutSubsoil Studyrcrt l(umr & Assoclates, lnc.6
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc oqrncd 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 I, CORYELL RANCH
CORYELL RANCH ROAI)
GARFIELD COUNTY, COLORADO
PROJECT NO. 21-7-493
JULY t9,2021
PREPARED FOR:
MICHAEL and SUZANNE DALTON
C/O PEAK 3 CONSTRUCTION + DEVELOPMENT
ATTN: BRYANTRAGAN
601 EAST HOPKINS AVENUE, SUrrE 202
ASPEN, COLORADO 81611
bryant@peak3 aspen.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ... - 3 -
PROPOSED CONSTRUCTION -3-
SITE CONDITIONS.-3-
SUBSIDENCE POTENTIAL.-4-
FIELD EXPLORATION -4-
SUBSURFACE CONDITIONS ............. - 5 -
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...
6-
-1-
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 . GRADATION TEST RESULTS
TABLE I _ SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, lnc. @ Project No.21-7-493
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PI]RPOSE AND SCOPE OF STT]DY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 8,
Coryell Ranch, Coryell Ranch Road, 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 sfudy was conducted in accordance with our agreement for geotechnical engineering
services to Michael and Suzanne Dalton dated I${ay 26,2021.
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 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
The proposed residence will be a one and two-story wood-framed structure with an attached
garage. Ground floors will be structural floor over crawlspace in the residence and slab-on-grade
for the garage. Grading for the structure is assumed to be relatively minor with cut depths
between about 3 to 6 feet. V/e 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 lot was vacant at the time of our visit. Vegetation consists of grass and weeds, with some
trees near the proposed garage location and at the northwest end of the lot. The ground surface is
relatively flat with a gentle to moderate slope down to the northwest. Elevation difference across
the building area is about 5 to 6 feet. The lot is bordered on the northwest by a pond and on the
southeast by Coryell Ranch Road.
Kumar & Associates, lnc. @ Project No.21-7-493
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SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the lower Coryell Ranch
Subdivision. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone
and limestone with some massive beds of gypsum. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite underlie portions of the property.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can
produce areas of localized, subsidence. During previous work in the area, several broad
subsidence areas and sinkholes have been observed. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley.
No evidence of subsidence or sinkholes were observed on the property or 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 can not
be said for certain that sinkholes will not develop. The risk of future ground subsidence at the
site throughout the service life of the structure, in our opinion is low, however the owner should
be 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 June 21, 2021. Three 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 and
Associates.
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-l586. 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 values are
shown on the Logs of Exploratory Borings, Figure 2. The samples,ù/ere returned to our
laboratory for review by the project engineer and testing.
Kumar & Asuocialtri, ltlr.;. o Project No. 21-7-493
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SUBSURF'ACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.The
subsoils, below about 6 inches of topsoil, consist of slightly silty to silty sandy gravel with
cobbles and probable small boulders down to the maximum depth explored, SYzfeet. Drilling in
the dense granular soils with auger equipment was difficult due to the cobbles and boulders and
drilling refusal was encountered in all three borings in the deposit.
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 llz-inch fraction) of the coarse gtanular subsoils are shown on Figure 3. The
laboratory testing is summarizedin 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 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.
l) 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
àrea.
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4)Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure coffesponding to an equivalent fluid unit weight of at least
45 pcf for the onsite sand and gravel as backfill.
All topsoil and any loose or 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.
5)
FLOOR SLABS
The natural on-site 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 well graded
sand and gravel (such as road base) should be placed beneath slabs for support. This material
should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less
than l2%o 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 fill can consist of the
on-site granular soils devoid of vegetation, topsoil, and oversized rock.
UNDERDRAIN SYSTEM
It has been our experience in the areathat local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. Vy'e recommend below-grade construction, such as retaining walls, crawlspace, and
basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and
wall drain system.
6)
Kumar & Associates, lnc. @ Project No. 2l-7"493
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The drains should consist of drainpipe placed in the bottom of the wall backfïll surrounded above
the invert level with free-draining granular material. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimumlo/oto
a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2Yopassing 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:
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 95o/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.
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 10 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.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this arca 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 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
Kumar & Associates, lnc. @ Project No. 21.7.493
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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 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. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continueà consultation and field services during construction to review and
monitor the implementation of our recoûrmendations, 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.
Respectfu lly Submitted,
Kumar & Associates, Inc.l#
David A. Noteboom, Staff Engineer
Reviewed by:
Steven L. Pawlak,
SLPlkac
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BORING 1
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BORING 2
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BORING 5
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LEGEND
TOPSOIL; SANDY CLAY AND GRAVEL wlTH ROOTS AND ORGANICS, FIRM, SLIGHTLY MOIST,
LIGHT BROWN.
GRAVEL (CP-CU); COBBLES, SANDY, SLIGHTLY SILTY TO SILTY, PROBABLE SMALL BOULDERS,
VERY DENSE, SLIGHTLY MOIST, LIGHT TAN AND LIGHT GRAY, ROUNDED ROCK.
I DRTVE SAMPLE, 1 S/9-|NCH t.D. SPLTT SPOON STANDARD PENETRATTON TEST.
27 /6 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 27 BLOWS OF A 14o-POUND HAMMER
FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 6 INCHES.
PRACTICAL AUGER REFUSAL.I
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 21 , 2021 WITH A 4-INCH DIAMETER
CONTINUOUS-FLIGHT POWER AUGER.
2. THE LOCATIONS OF ÏHE 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):
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (NSTV OOSIS);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl140).
WC=1.6
+4=60
-200= 1 0
WC=1.7
+4=55
-200=12
21-7 -493 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LIQUID LIMIT
SAMPLE OF: Sllghtly Sllty Sondy Grovel
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PLASTICITY INDEX
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LIQUID LIMIT
SAMPLE OF: Silly Sondy Grovel
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PLASTICITY INDEX
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FROM: Borlng 3 O 5' & 7,5' (Comblned)
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HYDROMETER ANALYSIS SIEVE ANALYSIS
II}¡E READINGS
24 HRS 7 HRS
U.S. STANDARD SERIES
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CLEAR SQUARÊ OPENINOS
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FINE MEDIUM COARSE FINE COARSE
HYDROMETER ANALYSIS SIEVE ANALYSIS
TIME READINGS
2ul HRS 7 HRS
U.S, STANDARD SERIES CLEAR SOUARE OPENINGS
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21-7 -493 Kumar & Associates GRADATION TEST RESULTS Fis. 5
lcrtå.ffilliffiffii,,rEü**TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-493J2PIT5 andTYzcombined2t/z and5combinedlfrlDEPTHSAI'PLE LOCATIONI71.6llrlNATURALMOISTURECONIENT{ocflNATURALDRYDENSITY60(%lGRAVEL553330(/,1SANDGRADATIONI210PERCENTPASSING NO.200 stEVELIQUID LttrilTlc/olPLASTICINDEXIololATTERBERG LII'ITS(psf)UNCONFINEDCOMPRESSTVESTRENGTHSilty Sandy GravelSlightly Silty Sandy GravelSOIL TYPE