HomeMy WebLinkAboutSubsoil Study Report 08.31.2018H -R K 5020 County Road 154
Glenwood Springs, CO 81601
Geotechnical Engineering I Engineering Geology Phone: (970) 945-7988
Materials Testing I Environmental Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 3, ORR SMITH SUBDIVISION
7004 COUNTY ROAD 312 (GARFIELD CREEK ROAD)
GARFIELD COUNTY, COLORADO
PROJECT NO. 18-7-520
AUGUST 31, 2018
PREPARED FOR:
KATIE+' JONES
P. O. BOX 906
NEW CASTLE, COLORADO 81647
Jones-y.kate@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY.......................................................................................- 1 -
PROPOSED CONSTRUCTION................................................................................................ - 1 -
SITECONDITIONS..................................................................................................................- 1 -
FIELD EXPLORATION
SUBSURFACE CONDITIONS.................................................................................................- 2 -
DESIGN
-DESIGN RECOMMENDATIONS............................................................................................. 2 -
FOUNDATIONS.................................................................................................................... - 2 -
FLOOR SLABS 3 -
-LIMISURFACEDRAINAGE........................................................................................................ - 4 -
LIMITATIONS
TATIONS...........................................................................................................................- 4 -
FIGURE
-FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURES 3 and 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
H-P-KUMAR
Project No. 18-7-520
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot 3,
Orr Smith Subdivision at 7004 County Road 312 (Garfield Creek Road) south of New Castle,
Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was
to develop recommendations for the foundation design. The study was conducted in accordance
with our agreement for geotechnical engineering services to you dated August 15, 2018.
A field exploration program consisting of exploratory pits was conducted to obtain information
on the subsurface conditions. Samples of the subsoils obtained during the field exploration were
tested in the laboratory to determine their classification, compressibility or swell and other
engineering characteristics. The results of the field exploration and laboratory testing were
analyzed to develop recommendations for foundation types, depths and allowable pressures for
the proposed building foundation. This report summarizes the data obtained during this study
and presents our conclusions, design recommendations and other geotechnical engineering
considerations based on the proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a two-story wood frame structure. Ground floor will be slab -on -
grade. Grading for the structure is assumed to be relatively minor with cut depths between about
2 to 3 feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The project site is currently vacant. Topography is valley bottom with slopes of 5 to 10 percent
down to the northwest. Garfield Creek borders the site to the north. Vegetation at the site
consists of native grass and weeds.
H-t'-KUW AR
Project No. 18-7-520
-2 -
FIELD EXPLORATION
The field exploration for the project was conducted on August 24, 2018. Two exploratory pits
were excavated at the locations shown on Figure 1 to evaluate the subsurface conditions. The
pits were dug with a rubber -tired backhoe. The pits were logged by a representative of H -P/
Kumar.
Samples of the subsoils were taken with relatively undisturbed and disturbed sampling methods.
Depths at which the samples were taken are shown on the Logs of Exploratory Pits, Figure 2.
The samples were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 2 to 2'/z feet of topsoil overlying slightly sandy clay and silt down to the
maximum depth explored of 8 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and percent finer than sand size gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples, presented on Figures 3 and 4, indicate
low to moderate compressibility under conditions of loading and wetting. One of the samples
exhibited a minor expansion potential when wetted under a constant light surcharge. The
laboratory testing is summarized in Table 1.
No free water was encountered in the pits at the time of digging and the subsoils were slightly
moist to moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory pits and the nature of the
proposed construction, we recommend the building be founded with spread footings bearing on
the natural fine-grained soils.
H-KKUNIIAR
Project No. 18-7-520
-3 -
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
An allowable bearing pressure of 2,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) 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 (if any) should also be designed to
resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at
least 55 pcf.
5) All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the stiff natural soils. The exposed
soils in footing area should then be moistened and compacted. If water seepage is
encountered, the footing areas should be dewatered before concrete placement.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
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-
H-P-KUMAR
Project No. 18-7-520
M
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 at least 50% retained on 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
imported granular soils such as road base devoid of vegetation, topsoil and oversized rock.
SURFACE DRAINAGE
The following drainage precautions should be observed during constriction 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.
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 paved areas. Free -draining wall backfill (if any)
should be capped with about 2 feet of the on-site soils to reduce surface water
infiltration.
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 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.
H-PEKUMAR
Project No. 18-7-520
-5 -
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, 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 so
that 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.
Respectfully Submitted,
H -P= KUMAR
p4e4l +
Robert L. Duran, E. I.
Reviewed by:
Daniel E. Hardin,
RLD/kac
cc: Brian Gandy
K: 24443 z
Project No. 18-7-520
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18-7-520 H—RWUMAR LOCATION OF EXPLORATORY PITS Fig. 1
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LEGEND
TOPSOIL; CLAY AND SILT, SLIGHTLY SANDY, FIRM, MOIST, DARK BROWN, ROOTS.
CLAY AND SILT (CL -ML); SLIGHTLY SANDY, STIFF, SLIGHTLY MOIST TO MOIST, TAN, POROUS,
MINOR ROOTS, INTERLAYERED, SLIGHTLY ORGANIC MATERIAL.
HAND DRIVEN LINER SAMPLE.
�- DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 24, 2018.
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 EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
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).
18-7-520 H-P%KUMAR LOGS OF EXPLORATORY PITS Fig. 2
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