HomeMy WebLinkAboutSubsoils Report for Foundation DesignK+AKumar & Associates, Inc. '1 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 81601
and Environmental Scientists phone: (970) 945-7988
email: kaglenwood@kumarusa.com
www.kumarusa.com
An Employee Owned Company
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
August 6, 2025
Dockers Construction
Attn: Dave Ockers
499 River Bend Way
Glenwood Springs, Colorado 81601
david dockersconstruction.com
Project No. 25-7-406
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot H34, Filing 7,
Aspen Glen, 200 Saddleback Road, Garfield County, Colorado
Dear Dave:
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 agreement for geotechnical \�
engineering services to Dockers Construction dated June 10, 2025. The data obtained and our Imo.
recommendations based on the proposed construction and subsurface conditions encountered �(
are presented in this report.
Proposed Construction: Plans for the proposed residence were conceptual at the time of our
study. The proposed residence is assumed to be a one- or two-story wood -frame structure with
attached garage located on the site in the area of the pits shown on Figure 1. Ground floors
could be structural over crawlspace or slab -on -grade. Cut depths are assumed to range
between about 2 to 5 feet. Foundation loadings for this type of construction are assumed to be M�
relatively light and typical of the proposed type of construction. 'V
If building conditions or foundation loadings are significantly different from those described
above, 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 was relatively flat and gently sloping down to the east. Vegetation consists of grass and
weeds.
Subsidence Potential: The subject site is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under
certain conditions can cause sinkholes to develop and can produce areas of localized
subsidence. Sinkholes have been observed in Aspen Glen development but not in the
immediate area of the subject lot. Based on our present knowledge of the site, it cannot be said
for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot
H34 is low and similar to other lots in the area but the owner should be aware of the potential for
sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
Dockers Construction
August 6, 2025
Project No. 25-7-406
Page 2
presented on Figure 2. The subsoils encountered, below about 1 foot of topsoil, consist of stiff
to very stiff, sandy clay to between 5 and 8Y2 feet deep. Below the clay, dense, silty sandy
gravel and cobbles was encountered to the maximum explored depth of 8% feet. Results of
swell -consolidation testing performed on relatively undisturbed samples of sandy clay,
presented on Figures 3 and 4, indicate low to moderate compressibility under conditions of
loading wetting. The laboratory test results are summarized in Table 1. No free water was
observed in the pits at the time of excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf
for support of the proposed residence. The clay soils tend to compress after wetting untie; Io6d
and there could be post -construction foundation settlement of around 1 inch. The settlement
potential can be mitigated by placing the footings on the dense underlying gravel soils. Footings
should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose
disturbed soils encountered at the foundation bearing level within the excavation should be
removed and the exposed soils moistened and compacted. 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 well reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 12 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 55 pcf for the on -site soil as backfill.
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 free -draining gravel should be placed beneath basement slabs -on -grade (if any) to
facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50%
passing the No. 4 sieve and 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 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 and where clay soils are present 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 pressure buildup by an underdrain system.
Kumar & Associates, Inc
Dockers Construction Project No. 25-7-406
August 6, 2025 Page 3
The drains should consist of rigid perforated PVC 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 Y2% to a suitable gravity outlet or drywell based in the underlying gravel
soils. 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 1Y2 feet deep and covered with filter
fabric such as Mirafi 140N or 160N.
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. 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.
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 pavement and walkway 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 sprinkler
heads should be located at least 5 feet from the building.
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 pits excavated at the locations
indicated on Figure 1 and to the depths shown on Figure 2, 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 pits 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 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 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 & Associates, Inc
Dockers Construction
August 6, 2025
Project No. 25-7-406
Page 4
monitor the implementation of our recommendations, and to verify 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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, Inc.
P&OW, it.
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak, i5222
JHP/kac •
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attachments Figure 1 +p plorato Pits
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Figure 2 — L ploratory Pits
Figures 3 and 4 — Swell -Consolidation Test Results
Table 1 — Summary of LaboratoryTest Results
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LOCATION OF EXPLORATORY PITS I Fig. 1
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LEGEND
® TOPSOIL; CLAY, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN.
CLAY (CL); SANDY, SLIGHTLY CALCAREOUS, STIFF TO VERY STIFF, SLIGHTLY POROUS,
SLIGHTLY MOIST, BROWN, BLOCKY IN UPPER PART.
o_
GRAVEL AND COBBLES (GM); SANDY, SILTY, DENSE, SLIGHTLY MOIST, BROWN, ROUNDED
ROCK.
HAND DRIVE SAMPLE.
NOTES
1.
THE
EXPLORATORY PITS WERE EXCAVATED WITH A
BACKHOE ON JUNE 11, 2025.
2.
THE
LOCATIONS OF THE EXPLORATORY PITS WERE
MEASURED APPROXIMATELY BY PACING FROM
FEATURES
SHOWN ON THE SITE PLAN PROVIDED.
3.
THE
ELEVATIONS OF THE EXPLORATORY PITS WERE
MEASURED BY HAND LEVEL AND REFER TO
PIT
1 AS A 100 FOOT ASSUMED BENCHMARK.
4.
THE
EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216).
25-7-406 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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