HomeMy WebLinkAboutObservation of Excavation~tee
HEPWORTH-PAWLAK GEOTECHNICAL
May 7, 2015
Chip Gilmore
P.O. Box 56
New Castle, Colorado 81647
(marionhurnett52@hotma ii .com )
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Job No. 115 162A
Subject: Observation of Excavation, Proposed Residence, 0895 County Road
216, Antonelli Lane, Garfield County, Colorado
Dear Mr. Gilmore:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
excavation at the subject site on April 20, 2015 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 20, 2015.
The proposed residence will be a one story wood frame structure over a crawlspace
with attached garage. The garage floor will be slab-on-grade. Foundations were
designed based on an assumed allowable soil bearing pressure of 1,500 psf.
At the time of our visit to the site, the foundation excavation had been cut in one level
from I to 4 feet below the adjacent ground surface. The soils exposed in the bottom
of the excavation consisted of medium stiff, sandy, silty clay. The footing subgrade
appeared to have been compacted. Results of swell-consolidation testing performed
on samples taken from the site, shown on Figure I, indicate the soils have low to
moderate compressibility under conditions ofloading and wetting. The samples had a
minor collapse potential (settlement under constant load) when wetted. No free water
was encountered in the excavation and the soils were 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 soil bearing pressure of 1,500 psf can be used for support of the proposed
residence. The exposed soils tend to compress when wetted and there could be post-
construction settlement of the foundation of possibly I inch depending on the depth of
wetting. Footings should be a minimum width of 16 inches for continuous walls and
2 feet for columns. Loose and disturbed soils in footing areas should be compacted or
removed and the bearing level extended down to the undisturbed natural soils.
Exterior footing.5 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 12 foet. Foundation walls acting as retaining structures should also be designed
P.nke r 'W1 -S41 -71 19 • C\)lor.idll Spring-. 719-6) 1-5562 • ~ilwrchnrnc 970-468-1989
Chip Gilmore
May 7, 2015
Page 2
to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 50
pcf for on-site soil as backfill. A perimeter foundation drain is not needed for the
garage slab-on-grade area and may not be needed for the proposed shallow
crawlspace (less than 4 feet) provided that backfill is properly placed and compacted
and good surface drainage is maintained around the residence. For a deeper
crawlspace, a perimeter drain should be provided to prevent temporary buildup of
hydrostatic pressure behind the foundation walls and prevent wetting of the deeper
crawlspace. An impervious membrane, such as 20 mil PVC should be provided
below the drain gravel in a trough shape and attached to the foundation wall with
mastic to prevent wetting of the bearing soils. Structural fill placed within floor slab
areas can consist of the on-site soils compacted to at least 95% of standard Proctor
density at a moisture content near optimum. Backfill placed around the structure
should be compacted and the surface graded to prevent ponding within at least I 0 feet
of the building. Landscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 5 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,
Rev. by: SLP
DEH/ksw
attachment Figure l -Swell-onsolidation Test Results
cc: Jack Palomino < jackpalomino55{tl !..!mail.com>
Kaup Engineering -Dale Kaup < dalefa ka ueen!..!ineerinu.com>
Job No . 115 162A
~tech
,
Moisture Content ,.. 15 8 percent
Dry Density = 103 pct
Sample of Sandy Si lty Clay
From · Bottom of Excavation.
0 North Side of Garage
-r--r----·o -
1 -
~ ....--Compress ion c::::: upon
* 2 ...... wett ing
§ ~ \ "(i'l
rn 3 Ql
5. ~t> E
0
(.)
4
0.1 1.0 10 100
APPLIED PRESSURE-ksf
Moisture Content == 15.2 percen t
Dry Density ~ 97 pct
Sample of Sandy Clayey Silt
From : Bottom of Excavation.
0 Sc utheast Corner of Hn11se
r--r---r-... too ro
1
·~ I:> Compression c::::: --upon
* 2 ~ welting
c ~ 0 ·en ' (/)
Ql .... 3 ' a.
E 11)
0
(.)
4
0.1 1.0 10 100
APPLIED PRESSU RE -ksf
115 162A ~ SWEL L-CONSOLIDATION TEST RESULTS Figure 1
HEPWORTH-PAWLAK GE:OTECHNICAL