HomeMy WebLinkAboutObservation of Excavation 04.19.2016G&tech
HEPWORTH-PAWLAK GEOTECHNICAL
April 19, 2016
Craig Whitlock
PO Box 1757
Glenwood Springs, Colorado 81602
sitewest@msn.com
}-icpworth-P.0 l:ik Geotc‘hnical,
5020 County Road 154
Glcnwood Spring, Ct lurid.) 81601
Phone 970 945.7988
F,,4 : 970-945-8454
email: hpgeo@hpgeotech corn
Job No. 116 112A
Subject: Observation of Excavation, Proposed Addition, Lot 19, Springridge Place,
314 Springridge Drive, Garfield County, Colorado
Dear Mr. Whitlock:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on April 14, 2016 to evaluate the soils exposed for
foundation support. The findings of our observations and recommendations for the
foundation design are presented in this report. The services were performed in
accordance with our agreement for professional engineering services to you, dated April
12, 2016.
The proposed addition will be attached to the south side of the residence and be a one and
two story structure with enclosed living space and open deck areas. The ground level
floor will be slab -on -grade. Spread footings placed on the natural soils and designed for
an allowable bearing pressure of 2,000 psf were assumed for the building foundation
support.
At the time of our visit to the site, the foundation excavation had been cut in two levels
from about 3 to 4 feet below the adjacent ground surface. Stacked boulder and concrete
retaining walls were located outside the uphill, west side of the excavation. The soils
exposed in the bottom of the excavation consisted of sandy silty clay. Results of swell -
consolidation testing performed on a sample taken from the site, shown on Figure 1,
indicate the soils have low to moderate compressibility under conditions of loading and
wetting. The results of an unconfined compressive strength test indicate very stiff
consistency. The laboratory test results are summarized in Table 1. No free water was
encountered in the excavation and the soils were typically slightly moist to moist.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural soil designed for an
allowable sail bearing pressure of 2,000 psf can be used for support of the proposed
addition with settlement potential. The exposed soils tend to compress when wetted
under load and there could be post -construction settlement of the foundation on the order
of 1 inch if the bearing soils become wet and precautions should be taken to keep the
Parker 303.841.7119 • Colorado Springs 719-633-5562 • Silverthome 970-468-1989
Craig Whitlock
April 19, 2016
Page 2
bearing soils dry. Footings should be a minimum width of 20 inches for continuous walls
and 2 feet for columns. Loose disturbed or soft soils in footing areas should be removed
and the bearing level extended down to the undisturbed natural soils. The bearing soils
should be protected against frost and concrete should not be placed on frozen soils.
Exterior footings should be provided with adequate soil cover above their bearing
elevations for frost protection. Continuous foundation walls should be 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 (if any) should also be designed to
resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for
on-site soil as backfill. Structural fill placed within floor slab areas should consist of
relatively well graded sand and gravel, such as road base, compacted to at least 95% of
standard Proctor density at a moisture content near optimum. Backfill placed around the
structure can consist of the onsite clay soils compacted and the surface graded to prevent
ponding within at least 10 feet of the building. Landscape that requires regular heavy
irrigation, such as sod, and sprinkler heads should not be located within 10 feet of the
foundation.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the foundation excavation and do not include subsurface exploration to
evaluate the subsurface conditions within the loaded depth of foundation influence. This
study is based on the assumption that soils beneath the footings have equal or better
support than those exposed. The risk of foundation movement may be greater than
indicated in this report because of possible variations in the subsurface conditions. In
order to reveal the nature and extent of variations in the subsurface conditions below the
excavation, drilling would be required. It is possible the data obtained by subsurface
exploration could change the recommendations contained in this letter. 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.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH — PAWLAK GEOTECHNICAL, INC.
Steven L. Pawlak, P.E. 15222
I)171442/10P-1
SLP/ksw :, 8* w1�:
Attachments: Figure 1— 5 ,i ; • ►.. ..
ion Test Results
Table 1— Summary of Laboratory Test Results
Job No, 116 112A
1
0
1
2
0 3
E 4
U
5
6
Moisture Content = 16.2 percent
Dry Density = 104 pcf
Sample of: Sandy Silty Clay
From: Approx Footing Elevation
Compression
upon
wetting
0.1
10
APPLIED PRESSURE - ksf
10
100
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Job No. 116 112A
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
1%)
NATURAL
DRY DENSITY
lam)
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
iPSF)
SOIL OR
BEDROCKTYPE
BOTTOM OF
EXCAVATION
DEPTH
[hl
GRAVEL
(%j
SAND
(%j
UQUID LIMIT
(%)
PLIC
INDEX
(%)
Southeast
Corner
31/2
16.2
104
•
Sandy Silty Clay
West Side
3
15.1
110
89
4,400
Sandy Silty Clay
IN