HomeMy WebLinkAboutSubsoils Report for Foundation DesigntGrtHl'rilfi'f,Tr:lt:fni'rvi*"'
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.gom
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
December 4,2024
Peak 3 Sundance, LLC
Attn: Bryant Ragan
310 Market Street
Basalt, Colorado 81621
bryant@feak3aspen.com
Project N o. 24-7 -208.02
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot SD-2, Aspen
Glen, Bald Eagle Way, Garfield County, Colorado
Dear Bryant:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations
at the subject site. The study was conducted as supplemental services to our agteement for
geotechnical engineering services to Peak 3 Sundance LLC, dated March 13,2024. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Constructiqn: The proposed residence will be a two-story wood-frame structure with
attached garage located on the site roughly between the pits shown on Figure 1. Ground floor
will be slab-on-grade for the garage and structural over crawlspace for the living areas. Cut
depths are expected to range between about 2 to 5 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: The subject site was vacant at the time of our field exploration. The ground
surface was relatively flat and gently sloping. There was evidence of minor cut and fill overlot
grading for subdivision development. Vegetation consisted of grass.
Subsurface Conditions: The subsurface conditions atthe site were evaluated by excavating
two 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 I to l% feet of topsoil, consist
of sandy clay to between 3% and 4t/z feet deep underlain by dense, silty sandy gravel and cobbles
to the maximum explored depth of 5 feet. Results of swell-consolidation testing performed on a
relatively undisturbed sample of sandy clay, presented on Figure 3, indicate low compressibility
under existing low moisture and light loading conditions and moderate to high collapse potential
(settlement under constant load) when wetted. No free water was observed in the pits at the time
of excavation and the soils were slightly moist.
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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 gravel soil, below the clay, designed for an allowable soil
bearing pressure o{:,000 prlfo^,rpport of the proposed residence. The gravel soils typically
possess a low settlement potential and post-construction foundation settlement should be minor.
Spread on a shallow depth of structural fill u to 3 feet on the
soils should an allowable soil bearing pressure of 1,500 psf.
footings placed on the undisturbed natural sandy clay soil designed for an allowable soil
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can a risk of
especially if the soil become wet.on experience, we expect initial
of footings will be less 1 inch. Additional, post-construction settlement could
occur if the clay bearing soils become wet. The magnitude of additional settlement would
depend on the depth and extent of wetting but could be on the order of Yzto 1 inch. The risk of
additional settlement could be reduced
fill.Structural fill should be moisture conditioned to near optimum
moisture content and
1,000
to at sity,
F
The topsoil, loose disturbed soils and existing fill encountered at the foundation bearing level
within the excavation should be removed and the footing bearing level extended down to the
undisturbed natural 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 heavily
reinforced top and bottom to span local anomalies such as by assuming an unsupported length of
at least 14 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 60 pcf for the on-site
soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded
slab-on-grade construction with a settlement risk. 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-on-grade for support. This material should consist of minus 2-inch
aggregate with less than 50o/o passing the No. 4 sieve and less than l2o/o passing the No. 200
sieve.
All fill materials for support of floor slabs should be compacted to at least 95o/o 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.
Kumar & Associates, lnc. @ Project No. 24.7-208.02
-J-
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 and crawlspace areas deeper than about 4 feet, be protected from wetting and
hydrostatic pressure buildup by an underdrain system. Crawlspace areas less than 4 feet deep
and slab-on-grade foundation areas should not need an underdrain system.
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 I foot below lowest adjacent finish grade and
sloped at a minimumYzo/o to a suitable gravity outlet or drywell in the gravels. Free-draining
granular material used in the underdrain system should contain less than 2o/o 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 1/z feet deep and covered with filter fabric such as Mirafi 140N
or 160N. An impervious membrane such as 20 mil PVC should be placed beneath the drain
gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of
the clay bearing soils.
Surface Drainage: Providing and maintaining proper surface drainage will be critical to
the long-term, satisfactory performance of the proposed residence. The following drainage
precautions should be observed during construction and maintained at all times after the
residence has been completed:
1) Inundation ofthe 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 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 aroas.
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 l0 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 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 inigation.
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
Kumar & Associates, lnc, @ Project No. 24-7-208.02
-4-
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 conskuction, 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 futrne. 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
recoilrmendations may be made.
This report has been prepared for the exclusive use by our client for design putposes. 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 verifu 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.
Respectfu lly Submitted,
Kumar & Associates, lnc.
9r'4tt r T. Paqx*u,/
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak,
JHPlkac
attachments
Figure 2 - Logs of Exploratory Pits
Figures 3 - Swell-Consolidation Test Results
Table 1 - Summary of Laboratory Test Results
Figure I Exploratory Pits
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Kumar & Associates, Inc. @ Project No. 24-7-208.02
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LEGEND
TOPSOIL; CLAY, SANDY, FIRM, ORGANICS, MOIST' BROWN.
cLAY (CL); SANDY, SILTY, MEDIUM STIFF TO STIFF, SLIGHTLY MOIST, BROWN, POROUS.
GRAVEL (GM); SANDY, SCATTERED COBBLES, SILTY, CLAYEY, MEDIUM DENSE TO DENSE,
SLIGHTLY MOIST, BROWN, ROUNDED ROCK.
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON NOVEMBER 8, 2024.
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 WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TEST RESULTST
Wc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (asrM D 2216);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4o).
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24-7-208.02 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Sondy Cloy
FROM:Pit8@2'
WC = 7.9 %, DD = 91 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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24-7-208.A2 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 3
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 24-7-208.02
8
7
PIT
SAMPLE LOCATION
2
3%
DEPI}I
{ft)
7.9
6.4
NATURAL
MOISTURE
CONTENT
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91
89
NATURAL
DRY
DENSlTY
locfl
ATTERBERG LIMITS UNCONFINED
COMPRESSIVE
STRENGTH
GRAVEL SAND PERCENT
PASSING NO.
200 srEVE
PLASTIC
INDEXLIQUID LIMIT(l"l (Y"l
86
Sandy Clay
Sandy Clay
SOIL TYPE