HomeMy WebLinkAboutObservation of Excavation 03.15.17H-PVKUMAR
Geotechnlcal Englneering I Engineeríng Geology
Materíals Testing I Envimnmenlal
5020 GountY Road 15¡t
Glenwood Springs, C0 81601
Fhone: (970) 945-7988
Far (970) 945'8454
Email: hpkglenwood@kumarusã.com
March 15,2017 Office Locations: Parker, Glenwood Splings, and Summit County, Colo¡ado
Lindsey Isham
177 Boom Plase
Rifle, Colorado 81650
lisham¡acing@aol.com
Project Na. 17-7-224
Subject:Observation of Excavation, Proposed Residence, 177 Boom Place, Northeast of
Rifle, Garf¡eld County, Colorado
Dear Líndsey:
As requested, a representative of H-PlKumar observed the excavation at the subject site on
March 13,2017 to evaluate the soils exposed for foundation support. The findings of our
observations and recommendations for the foundation desígn are presented in this report. The
services were performed in accordance with our agreement for professional engineering services
to you, dated March9,20l7.
An existing older house on the site has been removed and a new residence will be constructed.
The new residence will be a single story, pre-manufacfu¡ed wood frame sfructure over
crawlspace. The residence has been designed to be supported on 24-inch-wide continuous
spread footings. No soil bearing pressure is shown on the foundation plans by the structural
engineer.
At the time of our site visit, the foundation excavation which was essentially complete had been
cut in one level ûom about lVzto 3%feet below the adjacent ground surface. The soils exposed
in the bottom of the excavation consistEd of stiff, sandy to very sandy clayey silt with scattered
gravel and small cobbles. Results of swell-consolidation testing performed on samples taken
from the site, shown on Figure 1, indicate the soils are moderately compressible under conditions
of loading and wetting with a low hydro-compression potential. 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 I ,500 psf can be used for support ofthe proposed residence. The
exposed soils tend to compress when wetted and there could be some post-construction
settlement of the foundation if the bearing soils become wet. Settlements could be on the order
of I to 2 inches depending on tbe depth and extent of the wetting, Precautions should be taken to
prevent wetting of the bearing soils.
Footings should be a minimum width of l8 inches for continuous walls and 2 feet for columns.
Loose and disturbed soils in footing areas should be removed and the bearing level extended
down to the undisturbed natural soils, and the subgrade moistened and compacted. 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
Lindsey Isham
March 15,2017
Page 2
frost protection. Continuous foundation walls should be well reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls
acting as retaining structures should also be designed to resist a lateral earth pressure based on an
equivalent ftuíd unit weight of at least 50 pcf for on-site soil as backfill. A perimeter fou¡rdation
drain around the shallow crarvlspace should not be needed with adequate compaction of the
foundation backfill and positive surface slope away from the foundation walls. Backfill placed
around the structure should be compacted to at least 90% of standard Proctor density (95% in
pâvement areas) at a moisture content near optimum and the surface graded to prevent ponding
within at least l0 feet of the building. Landscape that requires regular heavy inigation, such as
sod, and sprinkler heads should not be located within l0 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 ofpossible
variations in the subsurface conditions. In order to reveal the natu¡e 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 concemed 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,
H-PÑKUIVIAR
David A. Young, P.
DAY/kac
Attachment Figure l, Swell-Consolidatión Test Results
cc: RodCo Concrete - Rodney Gaasch (rodney,. rodcoconcrete.com]
H.P*KUÍVIAR
Projecl No.17-7-224