HomeMy WebLinkAbout17-7-280.A (08-27-18) Partial ExcObs signed.pdf H 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
August 27, 2018
Vail Custom Builders
Attn: Benno Scheidegger
P. O. Box 2809
Edwards, Colorado 81631
benno@vailcustom.com
Project No. 17-7-280.A
Subject: Observation of Partial Excavation, Proposed Clifftop Residence, Lot 2, Cliffside,
1450 Buffehr Creek Road, Vail, Colorado
Dear Benno:
As requested, a representative of H-P/Kumar observed the partial excavation at the subject site
on July 30 and August 20, 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 as part of our agreement for construction observation and testing services to Vail
Custom Builders dated May 31, 2018.
We previously conducted a subsoil study for design of foundations at the site and presented our
findings in a report dated June 6, 2017, Job No. 17-7-280. The proposed construction is
generally similar to that discussed in our previous report. Spread footings bearing on the
relatively dense coarse granular soils designed for an allowable bearing pressure of 2,500 psf
were recommended for foundation support of the building. The deeper cuts on the west, north
and east sides of the excavation have been shored with a soil nail wall. Only the main residence
excavation is complete at this time and the attached garage and pool areas will be done at a later
date.
On July 30, the soil nail wall was nearly complete with some groundwater seepage encountered
near the bottom of the wall excavation, and topsoil and fine grained soils observed in the
southeast portion of the main residence excavation. At this time, we recommended a drain be
installed at the base of the soil nail wall and the topsoil and fine grained soils be removed in the
southeast excavation area of the residence.
At the time of our August 20 site visit, the foundation excavation for the main residence was
nearly complete and had been cut in three levels up to about 20 feet daylighting to the southwest.
Steps in grade between the excavation levels were from about 1 to 4 feet. The southwest portion
of the excavation had not been dug down to footing bearing elevation as this area was serving as
Vail Custom Builders
August 27, 2018
Page 2
access into the excavation. The soils exposed in the bottom of the completed excavation
consisted primarily of relatively dense, clayey to silty sand and gravel with cobbles. At the
southeast portion of the excavation, loose clayey silty sand was exposed at subgrade. Results of
swell-consolidation testing performed on a sample taken from the site, shown on Figure 1,
indicate these sand soils are moderately to highly compressible under conditions of loading and
wetting. While on site, we recommended the compressible sand soils be removed which we
observed to be done by sub-excavating down about 2 feet to expose the coarse granular soils at
subgrade. The groundwater seepage previously observed at the soil nail wall was being
controlled. The soils were generally slightly moist to moist.
The coarse granular soil conditions exposed in the excavation are consistent with those
previously encountered on the site and suitable for support of spread footings designed for the
recommended allowable bearing pressure of 2,500 psf. Loose and disturbed soils should be
removed in the footing areas to expose the undisturbed natural coarse granular soils and the
subgrade compacted. The southwest portion access into the excavation should have the footing
areas dug down to the coarse granular soils prior to constructing the footings. Other
recommendations presented in our previous report which are applicable should also be observed.
We should observe the garage and pool area excavations when completed to evaluate the bearing
conditions exposed.
The recommendations submitted in this letter are based on our observation of the soils exposed
within the foundation excavation and the previous limited subsurface exploration at the site.
Variations in the subsurface conditions below the excavation could increase the risk of
foundation movement. We should be advised of any variations encountered in the excavation
conditions for possible changes to recommendations contained in this letter.
If you have any questions or need further assistance, please call our office.
Sincerely,
H-P KU , . W e0108t`i
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David A. Young, PAjo
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attachment Figure 1, Swell-Consolidation Test Results
cc: Vail Custom Builders—Greg Johnson (greg@vailcustom.com)
H-PMKUMAR
Project No. 17-7-280A
SAMPLE OF: Clayey Silty Sand
FROM: Bottom of SE Portion of
Excavation 8-20-18
WC = 5.3 %, DD = 101 pcf
2
0
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
_2 DUE TO WETTING
—4
w
N
—6
= —
J 8
to
()—10
—12
—14
These teat results apply only to the
samples tested.The testing report
shall not be reproduced,except in
full,without the written approval of
Kumar and Associates,Inc.Swell
Consolidation testing performed in
accordance with ASTM 0-4546.
.1 1.0 APPLIED PRESSURE - KSF 10 100
s
s
f
s
0
.0
5 17-7-280A H-PtiKUMAR SWELL-CONSOLIDATION TEST RESULTS Fig. 1