HomeMy WebLinkAboutSubsoils Report for Foundation Designt
H EPWORTH.PAWLAK G EOTECHN ICAL
Maroh 21,2015
Phil & Lisa Ensign
I South Garfield Street
Denver, Colorado 80209
I-Ie1.rve61t-p,.rl'lak Gcotechnical, Inc.
5t120 Oounty Ro.rJ 154
(ilenrvoo.l Sl.linss, Colura.lo tl 1 (r0 1
Plr()nc: 97Ll-945-79lJtl
Flx: 97Lr-945-S454
etuail: hl.qe6@|pgcott'ch.c,rm
Job No. ll4 5428
H
subject: observation of Excavation, proposed Residence, Lot 23, High Aspen
Ranch, Overlook Drive, Garfield Counfy, Colorado
Dear Mr. & Mrs. Ensign:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the
driveway subgrade and excavation in the building areaatthe subject site on February
3,2015 to evaluate the soils exposed for foundation support. ThL findings of our
observations and recommendations for the foundation design are presented in this
report. The services were performed in accordance with our agre;ment for
professional engineering services to you, dated February 4,2015,
At the time of our visit to the site, the driveway had been rough graded and the
building arcahadbeen mass excavated and cut in one level up to 8 feet below the
adjacent ground surface. The soils exposed at the driveway cut grade and bottom of
the excavation in the building area consisted of basalt rocks from gravel to boulder
size in a sandy silty clay matrix. The results of a gradation arlalysis performed on a
sample of basalt gravel and cobbles in sandy clay matrix (minus 5 inch fraction)
obtained from the site are presented on Figure 1. The soils have a usDA
Classification of very gravelly sandy loam. No free water was encountered in the
excavation and the soils were moist.
Residence: Considering the conditions exposed in the building area excavation and
the nature of the proposed construction, spread footings placed on the undisturbed
natural soil designed for an allowable soil bearing pressure of 2,000 psf can be used
for support of the proposed residence. Footings should be a minimum width of l6
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. 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 10 feet. Foundation
walls acting as retaining structures should also be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 50 pcf for on-site soil as
Parker i0.3-841.7119 . Cobracio Springs 719-6i3"5562 r Silverthorne 9?0-468-1939
Phil & Lisa Ensign
March 27,20t5
Page2
b-ackfifl excluding rock larger than about 6 inches. A perimeter foundation drain
should be provided to prevent temporary buildup of hydrostatic pressure behind the
crawlspace and basement walls and prevent wetting of the lower level. 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 optinr-um. Backfill placed
around the structure should be compacted and the surface graOeA to prevent pottding
within at least 10 feet of the building.
Driveway Subgrade: The driveway subgrade appears stable. Low areas and holes
created by boulder removal should be backfilled with compacted structural fill
consisting of the on-site soils or a suitable imported granular material minus topsoil,
organics and over-sized rock. The structural fill should be compacted to at teast qS%
of the maximum standard Proctor density at a moisture content near optimum.
The recommendations submitted in this letter are based on our observation of the soils
exposed within the building area excavation and exposed driveway subgrade 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. thr rirk of
foundation movement may be greater than indicated in this report because of possible
variations in the subsurface conditions. Our services do not include determinlng the
presence, prevention or possibility of mold or other biological contaminants (UO3C)
developing in the future. If the client is concemed about MOBC, then a profissional
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.
Daniel Hardin, P
Rev. by: SLP
DEHlksw
attachment
cc:
Figure I - USDA Gradation Test Results
Thunder Construction - Monty Thomson (rnontv@thunderclevelt4lnrenj.coni)
High Country Engineering - Matt Langhorst (L{a!1@hgg:g.qA!t
tls"lt{
Job No. lt| 5428
G&ttecrt
24 HR. 7 HB
0 45 MlN. 15 MIN
TIME READINGS U.S, STANDARD SEFIES CLEAR SQUABE OPENINGS
60MlN1
l MIN-
9MtN.4 MtN. #32s #140 #60 #35 #18 *10 #4
100
90
80
70
10
20
30
6y40
tdu
F50ztdoEIJcL 60
602
6a
o-
50F zIJ()
v.trj
40 o-
70 30
80 20
90 10
100 0.001 .002 .005 .009 .019 .045 .106 .025 .500 1.00 2.00 4.75 9.5 19.0 37.5 76.2 152 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY
COBBL€S
GRAVEL 51 O/O SAND 11 %SILT 21 %CLAY 17 %
USDA SOIL WPE: Very Gravelly Sandy Loam FROM: Lot 23, High Aspen Ranch
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114 5428 USDA GRADATION TEST RESULTS Figure 1