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 6, BLOCK 3, SECTION 2, BATTLEMENT CREEK VILLAGE
47 VALLEY VIEW PLACE
GARFIELD COUNTY, COLORADO
PROJECT NO. 22-7-523
SEPTEMBER 26, 2022
PREPARED FOR:
RUSSELL CARTWRIGHT
35 WILLOWVIEW WAY
PARACHUTE, COLORADO 81635
russecart@gmail.com
Kumar & Associates, Inc. ® Project No. 22-7-523
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ....................................................................................... - 1 -
PROPOSED CONSTRUCTION ................................................................................................ - 1 -
SITE CONDITIONS ................................................................................................................... - 1 -
FIELD EXPLORATION ............................................................................................................ - 1 -
SUBSURFACE CONDITIONS ................................................................................................. - 2 -
FOUNDATION BEARING CONDITIONS .............................................................................. - 2 -
DESIGN RECOMMENDATIONS ............................................................................................ - 3 -
FOUNDATIONS .................................................................................................................... - 3 -
FLOOR SLABS ...................................................................................................................... - 4 -
SURFACE DRAINAGE ......................................................................................................... - 4 -
LIMITATIONS ........................................................................................................................... - 5 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 – LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 22-7-523
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 6, Block 3, Section 2, Battlement Creek Village, 47 Valley View Place, 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 Russell Cartwright dated July 25, 2022.
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, compressibility or
swell 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, recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The residence will be a single story wood frame structure located on the site as shown on
Figure 2. Ground floors will be a combination of structural over crawlspace in the living area
and slab-on-grade in the attached garage. Grading for the structure is expected to be relatively
minor with cut depths between about 3 to 5 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 lot was vacant and the ground surface appeared mostly natural at the time of our field
exploration. The terrain is relatively flat with strong slope down to the northwest. Vegetation
consists of scattered grass, weeds and sage brush. There are single family residences on the
adjacent lots.
FIELD EXPLORATION
The field exploration for the project was conducted on August 3, 2022. Two exploratory borings
were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The
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Kumar & Associates, Inc. ® Project No. 22-7-523
boring was 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.
Samples of the subsoils were taken with 1⅜-inch and 2-inch I.D. spoon samplers. The samplers
were 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 log of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountered, below about 1 foot of topsoil, consisted of very stiff to stiff, sandy to
slightly sandy silt underlain at depths from about 17 to 20½ feet by relatively dense, basalt gravel
and cobbles with boulders in a sandy silt and clay matrix. At depths from about 17 to 20½ feet at
Boring 2, a layer or zone of medium dense, silty clayey sand with scattered gravel was
encountered. Drilling in the coarse granular soils with auger equipment was difficult due to the
cobbles and boulders and drilling refusal was encountered in Boring 1 in the deposit.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density, and percent finer than sand size gradation analyses. Results of swell-
consolidation testing performed on relatively undisturbed drive sample of the silt soils, presented
on Figures 4 and 5, indicate low to moderate compressibility under conditions of loading. One
sample showed a low collapse potential and the other sample showed a minor expansion
potential when the samples were wetted under constant light surcharge. The laboratory testing is
summarized in Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The slightly sandy to sandy silt soils encountered at the site possess low bearing capacity and,
based on our experience in the area, tend to settle when wetted. Lightly loaded spread footings
bearing on these soils can be used for foundation support of the proposed residence with a risk of
settlement. To reduce the risk of settlement, we recommend a minimum 2 feet of the soils below
footing areas be removed and replaced in a moistened and compacted condition. The minor
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Kumar & Associates, Inc. ® Project No. 22-7-523
expansion potential encountered in one of the samples is believed to be an anomaly and can be
neglected in the foundation (and floor slab) design.
Placing the foundation on the underlying dense coarse granular soils such as with piles or piers
would provide a relatively low risk of foundation movement. Provided below are
recommendations for spread footings bearing on a minimum 2 feet of compacted structural fill
consisting of the on-site soils. Precautions should be taken to prevent wetting of the bearing
soils below the structural fill. Surface runoff, landscape irrigation and utility leakage are
possible sources of water which could cause wetting. If recommendations for piles or piers are
desired, we should be contacted to provided them.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we believe the building can be founded with spread footings bearing
on a minimum 2 feet of compacted structural fill with some risk of settlement. Precautions
should be taken to prevent wetting of the bearing soils below the structural fill.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on a minimum 2 feet of compacted structural fill should be
designed for an allowable soil bearing pressure of 1,200 psf. Based on
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less. There could be some
additional settlement if the bearing soils below the structural fill were to become
wetted. The magnitude of the additional settlement would depend on the depth
and extent of the wetting but may be on the order of ½ to 1 inch.
2) The footings should have a minimum width of 20 inches for continuous walls and
30 inches 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 heavily reinforced top and bottom to span
local anomalies and better withstand the effects of some differential settlement
such as by assuming an unsupported length of at least 14 feet. Foundation walls
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Kumar & Associates, Inc. ® Project No. 22-7-523
acting as retaining structures should also be designed to resist a lateral earth
pressure corresponding to an equivalent fluid unit weight of at least 50 pcf for the
onsite soils as backfill.
5) The topsoil, required depth of soil to provide 2 feet of structural fill, and any loose
disturbed soils should be removed in footing areas and the excavation extended
down to the natural soils. The exposed soils in footing areas should then be
scarified a depth of about 8 inches, moistened to near optimum and compacted.
The structural fill below the footings can consist of onsite soils, excluding
vegetation and topsoil, and should be compacted to at least 98% of standard
Proctor density at a moisture content within about 2% of optimum. Structural fill
should extend laterally beyond the edge of footings a minimum distance of one
foot.
6) A representative of the geotechnical engineer should observe all footing
excavations and test structural fill compaction on a regular basis 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 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 base course should be placed beneath slabs for support and to facilitate drainage.
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.
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 soils devoid of vegetation and topsoil, or of imported aggregate base course.
SURFACE DRAINAGE
A perimeter foundation drain around shallow (less than 4 feet) crawlspace areas should not be
needed with positive surface drainage away from foundation walls. The following drainage
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Kumar & Associates, Inc. ® Project No. 22-7-523
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 12 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation, such as sod, and lawn
sprinkler heads should be located at least 5 feet from foundation walls.
Consideration should be given to use of xeriscape to reduce the potential for
wetting of soils below the building caused by irrigation.
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
should provide continued consultation and field services during construction to review and
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Kumar & Associates
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Kumar & Associates
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 22-7-523
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 5 2.4 101 Sandy Silt
15 3.4 90 91 Slightly Sandy Silt
2 2½ 4.8 125 76 Sandy Silt
10 2.4 99 Sandy Silt