HomeMy WebLinkAboutSubsoil Study
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 7, CORYELL RANCH
399 CORYELL RANCH ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 21-7-571
AUGUST 3, 2021
PREPARED FOR:
REPPERT INVESTMENTS LP
ATTN: TODD REPPERT
10000 MEMORIAL DRIVE, SUITE 740
HOUSTON, TEXAS 77024
treppert@reppertcapital.com
Kumar & Associates, Inc. ® Project No. 21-7-571
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ....................................................................................... - 1 -
PROPOSED CONSTRUCTION ................................................................................................ - 1 -
SITE CONDITIONS ................................................................................................................... - 1 -
SUBSIDENCE POTENTIAL ..................................................................................................... - 2 -
FIELD EXPLORATION ............................................................................................................ - 2 -
SUBSURFACE CONDITIONS ................................................................................................. - 2 -
DESIGN RECOMMENDATIONS ............................................................................................ - 3 -
FOUNDATIONS .................................................................................................................... - 3 -
FLOOR SLABS ...................................................................................................................... - 4 -
UNDERDRAIN SYSTEM ..................................................................................................... - 4 -
SURFACE DRAINAGE ......................................................................................................... - 5 -
LIMITATIONS ........................................................................................................................... - 5 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 21-7-571
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 7,
Coryell Ranch, Coryell Ranch Road, Garfield 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 agreement for geotechnical engineering
services to Reppert Investments LP dated June 29, 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
Plans for the proposed residence were conceptual at the time of our study. In general, the
residence is proposed to be relatively large footprint structure in the northwestern end of the lot
roughly between the exploratory borings shown on Figure 1. will likely be a one and two-story
wood-framed structure with an attached garage. Ground floors will likely be a combination of
structural supported floor over crawlspace and slab-on-grade. Grading for the structure is
assumed to be relatively minor with cut depths between about 3 to 7 feet. We assume relatively
light foundation loadings, typical of the proposed type of construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The ground surface is sloping
down to the northwest gradually getting flatter to the northwest near the rear of the lot.
Vegetation consists of sparse grass and weeds. A pond is at the rear of the lot down to the
northwest. Coryell Ranch Road is to the southeast.
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Kumar & Associates, Inc. ® Project No. 21-7-571
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 was 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 July 13, 2021. Three exploratory borings
were drilled at the locations shown on Figure 1 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 a 1⅜-inch 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 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 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 ½ foot of topsoil overlying dense, slightly silty to silty sandy gravel
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Kumar & Associates, Inc. ® Project No. 21-7-571
with cobbles and probable boulders down to the maximum explored depth of 8½ feet. Drilling in
the dense granular soils with auger equipment was difficult due to the cobbles and boulders and
drilling refusal was encountered 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 1½-inch fraction) of the coarse granular subsoils are shown on Figure 3. 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 to 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.
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 1 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.
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 corresponding to an equivalent fluid unit weight of at least
45 pcf for the onsite sand and gravel as backfill.
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Kumar & Associates, Inc. ® Project No. 21-7-571
5) 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.
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 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 relatively
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 12% passing the No. 200 sieve. If a basement if proposed, the under slab gravel
should be relatively free draining with 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.
UNDERDRAIN 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, crawlspace and basement areas (if
any), 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 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to
a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain
system should contain less than 2% 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 1½ feet
deep.
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Kumar & Associates, Inc. ® Project No. 21-7-571
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation of the 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% 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.
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 10 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 finer graded
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
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 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
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Kumar & Associates
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 21-7-571
SAMPLE LOCATION NATURAL MOISTURE CONTENT
NATURAL DRY DENSITY
GRADATION
PERCENT PASSING NO. 200 SIEVE
ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH SOIL TYPE BORING DEPTH GRAVEL SAND LIQUID LIMIT PLASTIC INDEX (%) (%)
(ft) (%) (pcf) (%) (%) (psf)
1 2½ and 5
Combined 2.1 47 39 14 Silty Sandy Gravel
2 2½ and 5
Combined 1.9 57 33 10 Slightly Silty Sandy Gravel