HomeMy WebLinkAboutSubsoils Report for Foundation Designrcn Kumq & Assaclates, lne"6.
Gesteehnieal and Materiah fngineers 5020 County Road 154
and Hnvironmental $cienllsts Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
Aft BllFl{}yis Owntd Compcny www.kumarusa'-qen1
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSURFACE STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 3, GRAND HOGBACK SUBDMSION EXCEPTION
HARVEY GAP ROAI)
GARFIELD COUNTY, COLORADO
PROJECT NO.2t-7-702
NOVEMBER t,2021
PREPARED FOR:
JIM LORI)
827 RAILROAD AVENUE
RIFLE, COLORADO 81650
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS
FIELD EXPLORATION ......
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS..
UNDERDRAIN SYSTEM
SURFACE DRAINAGE
LIMITATIONS
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
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Kumar & Aesociates, lnc. o Project No. 21-7.702
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsurface study for a proposed residence to be located on
Lot2, Grand Hogback Subdivision Exemption, Harvey Gap Road, Garheld County, Colorado.
The project site is shown on Figure 1. 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 you dated August 13,202I.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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 built from shipping containers and may be supported on helical
- piers. Grading for the structure is assumed to be relatively minor with cut depths up to
3 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 site was vacant at the tirne of our site visit. A well had recently been installed. The house
site is relatively flat with relatively steep slopes down to the north just to the north of the
building area. Vegetation consists of pinon and juniper trees with minimal undergrowth. Harvey
Gap Reservoir is located to the north and downhill of the site. The site is located on the north
side of the Grand Hogback Monocline with runs east and west of the site.
FIELD EXPLORATION
The field exploration for the project was conducted on September 17,202I. Two exploratory
borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions.
Kumar & Associates, lnc. @ Project No. 21-7-702
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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 a 2 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-1586. The
penetration resistance values are an indication of the 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 encountered at the site are shown on Figure 2. The
subsoils consist of about 2 feet of stiff, sandy clayey silt with scattered sandstone fragments
overlying hard sandstone/siltstone bedrock of the Iles Formation. Drilling in the hard sandstone
bedrock with auger equipment was difficult due to the rock hardness and drilling refusal was
encountered in the deposit at about 1 1 feet in both borings.
Laboratory testing performed on a sample obtained from Boring 2 included natural moisture
content, density and Atterberg limits testing which indicated that the bedrock has low plasticity.
No free water was encountered in the borings at the time of drilling and the subsurface materials
were slightly moist.
FOUNDATION BEARING CONDITIONS
Shallow sandstone/siltstone bedrock of the Iles formation was encountered at shallow depth in
the borings. We expect that excavation of the bedrock with conventional excavators will be
possible but only for one to two feet. Helical piers are not an appropriate foundation for this site.
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 relatively shallow
spread footings bearing on the sandstone/siltstone bedrock.
Kumar & Associates, lnc. o Project No. 21-7.702
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed sandstone/siltstone bedrock should be
designed for an allowable bearing of5 ,000 psf. Based on experience, we
expect settlement of footings designed and constructed as discussed in this section
will be less than %inch.
2) The footings should have a minimum width of 16 inches for continuous walls and
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 required by the
County in this area. A shallower depth may be allowed for footings bearing on
the bedrock.
4) 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 (if any) should also be designed to
resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at
least 45 pcf.
5) All existing loose or disturbed soils or bedrock should be removed and the footing
bearing level extended down to the relatively intact bedrock.
6) 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 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 forjoint spacing and slab reinforcement should be established by the
designer based on experience and the intended slab use. All fill materials for support of floor
slabs should be compacted to at leastg5o/o of maximum standard Proctor density at a moisture
content near optimum. Required fill can consist of imported granular soils such as3/+-inchroad,
base devoid ofvegetation, topsoil and oversized rock.
Kumar & Associates, lnc. @ Project No. 21-7-702
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UNDERDRAIN SYSTEM
An underdrain system should not be needed for the proposed shallow excavation. If below grade
crawlspace or basement areas are expected, we can provide appropriate drain recommendations.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
l) 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 90% of the maximum standard Proctor density in landscape areas.
2) 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
2Yz inches in the first l0 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
LINIITATIONS
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 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
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 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 continued consultation and field services during construction to review and
Kumar & Aesociates, lnc. @ Project No. 21-7-702
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monitor the irnple:nentatir:n erf our rscr:mmendations" and tc v*rify that the rscoffin*ndations
hav* been appropriately int*rpreted. $ignifica:rt design changes may requir* aelditional analysis
ar maditi*ations tc the r*slrn:nondati*ns presented her*in. W* reeomm*n*i on-site observati*n
erf excavatiE:*s and foundati*n b*aring strata and testing af struetural lill by a representafive ofl
the geotecfu:ieal engin*er.
Respectfu lly Subntitted-
K*:u**x" & Ass**i*tes, I*c*.
Saniel E. Harrlin, F
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Kumnn & Asm**iates, ln*. +Pr*jcct F,l*, ?{-7"70?
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APPROXIMATE SCALE-FEET
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21-7-702 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1
EL. 1 00'
BORING 2
EL. 97,
0 0
56/6 64/12
5 50/s
WC=5.1
DD=113
LL=27
Pl=11
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LEGEND
cLAy AND StLT (CL-ML); SANDY, SCATTERED ROCK FRAGMENTS, STtFF, SLIGHTLY MO|ST,
BROWN.
SANDSTONE, SILTSTONE: HARD, SLIGHTLY MOIST, GRAYISH BROWN, ILES FORMATION
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
^a/12
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 64 BLOWS OF A 140-POUND HAMMER-'f '- FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
I enacrrcaL AUGER REFUSAL.
NOTES
1 THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 17,2021 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.
5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER
TO THE GROUND SURFACE AT BORING 1 AS 1OO.O FEET.
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 (PCt) (NSTV D2216):
LL = LIQUID LIMIT (ASTM D4318);
Pl = PLASTICITY INDEX (ASTM D4318).
21 -7 -702 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2