HomeMy WebLinkAbout18-7-434 (07-27-18) NE Patio Exc Obs signed.pdf H-P KU mAR5020 County Road 154
Glenwood Springs, CO 81601
Geotechnical Engineering I Engineering Geology Phone: (970)945-7988
Materials Testing I Environmental Fax: (970)945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver(HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
July 27, 2018
Howard Rapson Construction
Attn: Howard Rapson
P. O. Box 5664 •
Vail, Colorado 81658
Hrapski7@gmail.com
Project No. 18-7-434
Subject: Observation of Excavation, Proposed Northeast Patio Addition to Hanson
Residence, Unit 15, 770 Potato Patch Drive, Vail, Colorado
Dear Howard:
As requested, a representative of H-P/Kumar observed the excavation at the subject site on July
16, 2018 to evaluate the soils exposed for foundation support. The findings of our observations
and recommendations are presented in this report. The services were performed in accordance
with our agreement for professional engineering services to Howard Rapson Construction dated
June 22, 2018. We previously observed the excavation for the southeast deck addition area and
presented our findings in a report dated June 28, 2018, Project No. 18-7-434.
The low site retaining wall will be attached to the northeast portion of the residence. The wall
has been designed to retain a flagstone patio on its south side. The spread footings to support the
wall have been sized assuming an allowable soil bearing pressure of 1,500 psf.
At the time of our site visit, the foundation excavation for the site wall had been cut in one level
from 5 to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the
excavation consisted primarily of relatively dense, silty sand and gravel with cobbles. 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 granular soil designed for an
allowable bearing pressure of 1,500 psf can be used for support of the proposed site wall/patio
addition. There could be some differential settlement with respect to the existing structure which
should be considered in the design. Footings should be a minimum width of 18 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 granular soils, and the
subgrade compacted. The 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
Howard Rapson Construction
July 27, 2018
Page 2
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 granular soil
(minus 6-inch fraction) as backfill. A perimeter foundation drain should be provided to prevent
temporary buildup of hydrostatic pressure behind the site wall. Backfill of the foundations can
consist of the on-site granular soils compacted to at least 90% of standard Proctor density (95%
in pavement areas) at a moisture content near optimum. Backfill placed around the site wall and
building should have the surface graded to prevent ponding within at least 10 feet of the wall,
building, and foundations.
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 andextent 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.
If you have any questions or need further assistance, please call our office.
Sincerely,
H-Pt KUMAR
Robert L. Duran, E. I.
Reviewed by: ,or. w *F *
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David A. Young, PaN,7 3Q` t� .:
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cc: Town of Vail—CJ Jarecki (cjarecki@vailgov.com)
Project No. 18-7-434