HomeMy WebLinkAboutSubsoils Report for Foundation DesignK+AKumar ni Associates, Inc.® 5020 County Road 154
Geotec
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
October 10, 2025
Aspen Valley Land Trust
Attn: Brian Hightower
320 Main Street, Suite 204
Carbondale, Colorado 81623
brian(aD-avlt.org
Project No. 25-7- 204
Subject: Subsoil Study for Foundation Design, Proposed Ranch Development, Phase 1,
1837 County Road 100 (Catherine Store Road), Aspen Valley Land Trust, Garfield
County, Colorado
Gentlemen:
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 Aspen Valley Land Trust dated July 29, 2025. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered
are presented in this report.
Proposed Construction: The proposed ranch development, Phase 1, will consist of various
buildings including a multi -purpose building, pole barn, ranch shop, ag buildings, and community
kitchen located on the site as shown on Figure 1. Ground floors will be slab -on -grade. Cut depths
are expected to be up to about 3 feet. Foundation loadings for this type of construction are
assumed to be relatively light and typical of the proposed type of construction.
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: There are existing cabins and ranch buildings at the site. Topography is valley
bottom gently sloping terrain down to the north. Vegetation consists of native grass, weeds, and
hay fields. An irrigation ditch borders the project site to the north.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating 7
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about'/2 to 2 feet of topsoil or granular
Aspen Valley Land Trust Project No. 25-7-204
October 10, 2025 Page 2
fill, consist of dense sandy silty gravel and cobbles and small boulders down to the maximum
depth explored of 4 feet. Results of a gradation analysis performed on a sample of gravel (minus
5-inch fraction) obtained from the site are presented on Figure 4. Free water was observed in the
pits at depths of 2 to 3 feet at the time of excavation and the soils were moist to wet.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings or
mat slabs placed on the undisturbed natural granular soil designed for an allowable soil bearing
pressure of 3,000 psf or subgrade modulus of 250 tcf for support of the proposed ranch
development buildings. Footings (or thickened slab sections) shouldbe a minimum width of 18
inches for continuous walls and 2 feet for columns. The topsoil, existing fill and loose disturbed
soils encountered at the foundation bearing level within the excavation should be removed and
the footing bearing level extended down to the undisturbed natural granular soils. 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 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 be designed to resist a lateral earth pressure based on an
equivalent fluid unit weight of at least 45 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, non-structural
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 slabs 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 gravel soils devoid of vegetation, topsoil and oversized rock.
We recommend vapor 'retarders conform to at least the minimum requirements of ASTM El745
Kumar & Associates, Inc
Aspen Valley Land Trust
October 10, 2025
Project No. 25-7-204
Page 3
Class C material. Certain floor types are more sensitive to water vapor transmission than
others. For floor slabs bearing on angular gravel or where flooring system sensitive to water
vapor transmission are utilized, we recommend a vapor barrier be utilized conforming to the
minimum requirements of ASTM E1745 Class A material. The vapor retarder should be
installed in accordance with the manufacturers' recommendations and ASTM E1643.
Underdrain System: It is our understanding the proposed finished floor elevation at the lowest
level is at or above the surrounding grade. Therefore, a foundation drain system is not required.
It has been our experience in mountainous areas 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 and wall drain system. A shallow crawlspace should not need to be protected
with an underdrain with proper foundation wall backfill and surface grading.
If the finished floor elevation of the proposed -structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the structures have 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 2 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.
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
Kumar & Associates, Inc.®
Aspen Valley Land Trust Project No. 25-7-204
October 10, 2025 Page 4
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
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 & Associate:
Robert L. Duran, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
RLD/Ijf
Attachments: Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 - Legend and Notes
Figure 4 — Gradation Test Results
cc: Wember — Joe Farstad ifarstad wemberinc,com)
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LOCATION OF EXPLORATORY BORINGS
13
Fig. 1
LEGEND
® TOPSOIL; SILTY SANDY CLAY WITH SCATTERED GRAVEL, FIRM, MOIST, DARK BROWN, ROOTS.
FILL; SILTY SANDY GRAVEL AND COBBLES WITH SCATTERED BOULDERS, MEDIUM DENSE,
MOIST, BROWN, MINOR DEBRIS.
GRAVEL AND COBBLES (GP —GM); VERY SANDY, SILTY, SCATTERED SMALL BOULDERS UP TO
ABOUT 1' DIAMETER, DENSE, WET, BROWN, SUB —ROUNDED ROCK.
r j DISTURBED BULK SAMPLE.
IL J
0 DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING.
DEPTH AT WHICH PIT CAVED.
t PRACTICAL REFUSAL TO THE EXCAVATION.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 13, 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 NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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 LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
25-7-204 1 Kumar & Associates
LEGEND AND NOTES
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HYDROMETER ANALYSIS
SIEVE ANALYSIS
TIME READINGS
%U. STANDARO SLiiIES
CLEAR ""ARE dPEHIN05
24 HRS
7 XRS
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DIAMETER OF PARTICLES IN MILLIMETERS
152
CLAY TO SILT SAND
GRAVEL COBBLES
FINE MEDIUM COARSEJ FINE COARSE
Cobbles 16 % GRAVEL 47 % SAND 28 Y.
SILT AND CLAY 9 %
LIQUID LIMIT — PLASTICITY INDEX —
SAMPLE OF: Slightly Silty Sandy Gravel with Cobbles FROM: Pit 4 ®
2'-3'
These test results apply only to the
samples which were tested. The
testing report shall not be reproduced,
except In full, without the written
approval of Kumar h Associates, Inc.
Sieve anGlysis resting la performed In
aceerdanee w1lh ASt9 D9913, ASTM D7928,
ASTN C136 and/or ASTM 01140.
25-7-204
Kumar & Associates GRADATION TEST
RESULTS
Fig. 4