HomeMy WebLinkAboutSubsoil Study for Foundation Design 01.14.19H.P=KUMAR 5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Geotechnical Engineering I Engineering Geologv
Materials Testing I Environmental
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
January 14,2019 RECEIVED
ÅPl? tl 3 ?Û1$Gruenefeldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado 81621
dan@gruenefeldt.com
Project No.l8-7-752
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot El8, Aspen
Equestrian Estates,29 Equestrian Way, Garfield County, Colorado
Dear Dan:
As requested, H-P/Kumar 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 you dated December 28,2018. The data obtained and our recofirmendations based on
the proposed construction and subsurface conditions encountered are presented in this report.
Proposed Construction: The proposed residence will be a one to two story wood frame
structure located on the site in the area of the pits as shown on Figure 1. Ground floor will be
slab-on-grade. A monolithic slab foundation is being considered. Cut depths are expected to
range between about l% to 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: The lot was vacant at the time of our site visit. The lot is flat, slopes slightly
down to the south and is vegetated with grass and weeds. Eagle Valley Evaporite bedrock is
exposed on the valley hillsides to the north and south. There was around 6 inches of snow cover
at the time of our site visit.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
five 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 8 inches of topsoil, consist of one
GARFIELD COUNTY
COMMUNITY DEVELOPMEITIT
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to four feet of medium stifi sandy silty clay overlying relatively dense, silty sandy gavel with
cobbles and small boulders down to the maximum depth explored, 5Yz feet. Free water was not
encountered at the time of excavation and the upper subsoils were moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recoûrmend spread footings or a
thickened edge slab foundation placed on the undisturbed natural clay soil designed for an
allowable soil bearing pressure of 1,200 psf for support of the proposed residence. The clay soils
tend to compress under load and there could be some post-construction foundation settlement.
Footings or the thickened slab edge should be a minimum width of 18 inches for continuous
walls and 2 feet for columns. Loose and disturbed subsoils encountered at the foundation
bearing level within the excavation should be compacted or removed and the footing or
thickened edge 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.
Shallower footings or thickened slab edges should be protected from frost with insulation in
accordance with the International Residential Code. Continuous foundation walls (if any) 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 (if any) should be designed to
resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the
on-site soil as backfill.
Non-structural 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
movernent, 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 act as a
break for capillary moisture rise. This material should consist of minus 2 inch aggregate with
less than 50olo passing the No. 4 sieve and less than2o/o passing the No. 200 sieve.
Project No.18-7-752
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All fill materials for support of floor slabs should be compacted to at least 95%o of maximum
stan<lard Proctor density at a moisture content ncar optimum. Requirecl fill can consist of
imported gravel such as road base devoid of vegetation, topsoil and oversized rock.
Underdrain System: An underdrain should not be needed for the proposed slab at or above
surrounding grade construction.
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 95o/t of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/o 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/zinches 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 should be located at least
5 feet from the building. Consideration should be given to the use of xeriscape to
limit potential wetting of soils below the foundation 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 pits excavated at the locations indicated on Figure I
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
Project No. 18-7-752
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findings include interpolation and extrapolation of the subsurface conditions identified at the
exploratory pits and variations in the subsutface conditions may not become evident until
excavation is perfonned. If conditions encoutttered during construction appear difièrent 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 recofiìmendations, and to verify that the recoîrmendations
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 funher assistance, please let us know
Respectfully Submitted,
H-P*KUMAR
James H. Parsons, E.I
Reviewed by:
Daniel E. Hardin, P
JHP/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Legend and Notes
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Project No. 18-7-752
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18-7 -752 H-PVKUMAR LOGS OF EXPLORATORY PITS Fig. 2
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LEGEND
TOPSOIL; ROoT ZONE, SANDY SILTY CLAY, ORGANIC, MOIST, SOFT, DARK BROWN.
CLAY (CL); SILTY, SANDY, MEDIUM STIFF, SLIGHTLY MOIST, BROWN.
GRAVEL (GM-GP); SANDY, SLIGHTLY SILTY, WITH COBBLES AND SMALL BOULDERS, DENSE,
MOIST, BROWN.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 2, 2019
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 OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 DRILLING. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
18-7 -752 H-PVKUMAR LEGEND AND NOTES Fig. 3
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