HomeMy WebLinkAboutSoils Report 04.26.2006April 26, 2006
Dianne Kroeger
1375 Green Meadow Drive
Carbondale, Colorado 81623
Hepworth-Pawlak Geotechnical, Inc.
5020 Count v Road 154
Glenaaxul Springs, Colorado 51601
Phone: 970-945-7988
Fax: 970-945-8454
eurri1: hpr:eo@hpl;eorech.com
Job No. 106 0293
Subject: Subsoil Study for Foundation Design, Proposed Residence, 7207 County
Road 100, Garfield County, Colorado
Dear Ms. Kroeger:
As requested, Hepworth-Pawlak Geotechnical, 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 5, 2006. 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, wood frame
structure with an attached garage supported by a "Superior Walls" foundation and be
located on the site as shown on Figure 1. Ground floors will be slab -on -grade. Cut
depths are expected to range between about 3 to 5 feet. Foundation loadings 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 at the time of our field exploration and consists of
pasture land. The approximate building corners were staked in the field and a driveway
was being graded into the building area. County Road 100 (Catherine Store Road)
borders the property to the east. A shared access drive crosses the property at the north
end. The topography in the area consists of gently rolling hills with an overall slope
down to the south. The ground surface in the proposed building area is relatively flat
with a gentle slope down to the north. Vegetation in the proposed building area consists
of grass.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating two exploratory pits at the approximate locations shown on Figure 1. The
Parker 303-841-7119 0 Colorado Springs 719-633-5562 Silverrhornc 97046S-1989 -1989
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logs of the pits are presented on Figure 2. The subsoils encountered, below about 1 to 2
feet of organic topsoil, consist of sandy silty clay down to the maximum pit depths of 8
feet. Results of swell -consolidation testing performed on relatively undisturbed samples
of the clay, presented on Figure 3, indicate low to moderate compressibility under
conditions of loading and wetting. No free water was observed in the pits at the time of
excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend foundations
placed on the undisturbed natural soil designed for an allowable soil bearing pressure of
1,500 psf for support of the proposed residence. The clay soils tend to compress under
load and there could be some post -construction foundation settlement, especially if
wetted. Loose and 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. 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,
if any, should be designed to resist a lateral earth pressure based on an equivalent fluid
unit weight of at least 55 pcf for the on-site soil as backfill. The Superior Wall
foundation appears feasible provided some differential settlement of about 1 inch can be
tolerated.
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 sand and gravel should be placed beneath interior
slabs for subgrade support. This material should consist of minus 2 inch aggregate with
less than 50% passing the No. 4 sieve and less than 12% 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.
Job No. 106 0293
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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.
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
Job No. 106 0293
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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,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Trevor L. Knell, P.
Reviewed by:
•
Steven L. Pawlak, P.E.
TLK/ksw
attachments
Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Swell -Consolidation Test Results
Table 1— Summary of Laboratory Test Results
cc: Santis Engineering — Attn: Chris Santistevan
Superior Walls of the Rockies — Attn: Bob Benjamin
Job No. 106 0293
Gtech
DEPTH - FEET
0
5
10
LEGEND:
1/a
PIT 1 PIT 2
WC=21.6
DD=95
WC=20.2
DD=94
WC =21.5
DD= 103
10
TOPSOIL; sandy clay, roots, firm, moist, dark brown to black.
CLAY (CL); sandy, slightly silty to silty, medium stiff to stiff, moist, reddish brown, slightly calcareous with depth,
2" Diameter hand driven liner sample.
NOTES:
1, Exploratory pits were excavated on April 5, 2006 with a Caterpillar 416 Turbo 4x4 backhoe.
2. Locations of exploratory pits were measured approximately by pacing from building corners staked in the field and
shown on the site plan provided.
3. Elevations of exploratory pits were not measured. Pit 1 is estimated to be about 6 feet higher in elevation than Pit 2.
The logs of exploratory pits are drawn 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 transitions may be gradual.
6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (% )
DD = Dry Density ( pcf )
DEPTH - FEET
106 0293
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HEP WORTH•PAWLAF[ GEOTECHNICAL
LOGS OF EXPLORATORY PITS
FIGURE 2
COMPRESSION (% )
COMPRESSION (% )
0
1
2
0
1
2
01
0
1 0 10
APPLIED PRESSURE ( ksf )
100
IIIIII111
111111
:7:13.1e4 S'n4dFY:tiaY
Moisture Content = 20.2 percent
Dry Density = 94 pcf
Sample of: Sandy Clay
From: Boring 1 at 7 1/2 Feet
111
um
11111
1111
11
amirdiii...---mseiniiims!
NumummoilmtNuornwern'en
111111111111011111111111
Eim
11111.110
mai
1111111,
111110
11111!
N. No movement
upon wetting
01
0
1 0 10
APPLIED PRESSURE ( ksf )
100
IIIIII111
111111
:7:13.1e4 S'n4dFY:tiaY
111
um
11111
1111
11
amirdiii...---mseiniiims!
NumummoilmtNuornwern'en
111111111111011111111111
Eim
11111.110
mai
1111111,
111110
11111!
APPLIED PRESSURE ( ksf )
0
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GIZIStech
HEPWORTH-PAWLAK GEOTECHNICAL
SWELL -CONSOLIDATION TEST RESULTS
FIGURE 3
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Job No. 106 0293
SAMPLE LOCATION
NATURAL NATURAL 1
MOISTURE DRY I
CONTENT DENSITY
GRADATION 1ATTERSERG
PASSING
NO. 200
SIEVE
LIMITS
UNCONFINED 1
COMPRESSIVE
STRENGTH
SOIL
TYPE
PIT NO.
DEPTH
�
I PERCENT
GRA VEL SAND
(%} (%)
I
LIQUID
LIMIT
, PLASTIC
INDEX
1
3 21.6
95
Sandy clay
71
20.2
94
Sandy clay
2
4
21.5
103
Sandy clay
r
EXISTING ROAD—
PIT 2
PROPOSED
RESIDENCE
nOG
90
":°
a$
7207 COUNTY ROAD 100
PIT 1
APPROXIMATE SCALE:
1"=80'
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GegUech
HEPWORTH-PAWLAI{GEOTECI-1NIC L
LOCATION OF EXPLORATORY PITS
FIGURE 1