HomeMy WebLinkAboutSubsoil Study'UARte& Inc. 5020 County Road 154
Geotechnical and Materials Engineers Glenwood Springs, CO 81601
and Environmental Scientists phone: (970) 945-7988
Z fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
May 9, 2019
James Armstrong
143 Garfield Avenue
Carbondale, Colorado 81623
armstrong_ james04Agmall. corn
Project No. 19-7-268
Subject: Subsoil Study for Foundation Design, Proposed Residence, 16 Panorama Drive,
Homestead 16, Panorama Ranches, Garfield County, Colorado
Dear Mr. Armstrong,
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 you dated April 18, 2019. The data obtained and our recommendations
based on the proposed construction and subsurface conditions encountered are presented in this
report.
Proposed Construction: The proposed residence will be a single story structure with a walkout
basement and garage located on the site as shown on Figure 1. Ground floor will be slab -on -
grade or structural over crawlspace. Cut depths are expected to range between about 3 to 8 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 site was vacant during our site visit. The natural terrain slopes down to
the southwest at about 10% to 25% grade. The ground surface is vegetated by sage brush, scrub
oak, grass, and weeds. Panorama Drive and one- to two-story residence are south, vacant lots are
to the east and north, and a gravel road is to the west of the site.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two
exploratory pits which had been dug prior to our site visit at the approximate locations shown on
Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered generally
consisted of a mixture of natural clay, sand, and gravel. No free water was observed in the pits
and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
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placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 1,500
psf for support of the proposed residence. The soils tend to compress after wetting under load
and there could be some post -construction foundation settlement up to around 1 inch. Footings
should be a minimum width of 18 inches for continuous walls and 2 feet for columns. The
topsoil 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 soils. We should observe the completed foundation excavation prior to concrete
placement. 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 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 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils other than topsoil are suitable to support lightly loaded
slab -on -grade construction with a low risk of settlement similar to spread footings. 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 level 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 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 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.
The drains should consist of 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 1 % to
a suitable gravity outlet. 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 1 %2 feet deep.
Kumar & Associates, Inc. Project No. 19-7-268
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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 in 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 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
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
Kumar & Associates, Inc. Project No. 19-7-268
W
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.
Shane J. Robat, P.E., Project Manager
Reviewed by:
Steven L. Pawlak, P
SJR/kac
attachments
Pits
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. 19-7-268
50.0'
SETBACK
PIT 2• \ \ 1\ \\ \\
\dui rr
PIT I OAK
LOT 16
-� LS 3 44\ \ \ \ \ \ \ \ \ \ \
L< SCF 0-
ILLEGIBLE
30 0 30 60
APPROXIMATE SCALE -FEET
19-7-268 Kumar & Associates LOCATION OF EXPLORATORY PITS
50.0'
SETBACK
Fig. 1
LEGEND
TOPSOIL; ORGANIC,
SANDY, SILT AND CLAY, FIRM, BROWN, MOIST.
CLAY
(CL);
SANDY TO VERY SANDY, GRAVELLY, STIFF, MOIST, MEDIUM BROWN.
SAND
AND
CLAY (SC—CL); GRAVELLY, MEDIUM DENSE/STIFF, LIGHT BROWN.
SAND
(SC);
CLAYEY, SCATTERED GRAVEL, MEDIUM DENSE, MOIST, TAN.
SAND
(SM);
SILTY, MEDIUM DENSE, SLIGHTLY MOIST, YELLOW BROWN.
SAND
AND
GRAVEL (SC—GC); SLIGHTLY CLAYEY, MEDIUM DENSE, MOIST, MIXED BROWN.
HAND
DRIVEN 2—INCH DIAMETER LINER SAMPLE.
DISTURBED
BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS HAD BEEN EXCAVATED WITH A BACKHOE AND OBSERVED ON MAY 1,
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. GROUND WATER WAS NOT OBSERVED IN THE PITS.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
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19-7-268 Kumar & Associates LEGEND AND NOTES Fig. 3
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