HomeMy WebLinkAboutDRB17-0078_ENGINEERING LETTER_1489502940.pdf H.p ti Ku NAAR 5020 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
March 6, 2017 Office Locations: Parker,Glenwood Springs,and Summit County,Colorado
Crestone Building Company
Attn: Scott Hoffman
501 West Hallam
Aspen, Colorado 81611
scott@crestonebuilding.com
Project No. 16-7-508.A
Subject: Recommendations for Temporary Excavation Cut Slopes, Proposed Residences,
Lots 1 and 2, Block 3, Bighorn 3rd Addition, 4367 and 4387 Columbine Drive,
Vail, Colorado
Dear Scott:
As requested, we are providing recommendations for temporary excavation cut slope grades for
the proposed project at the subject site. This letter summarizes the assumed excavation
conditions and our recommendations. The services are supplemental to our agreement for
professional engineering services to Crestone Building Company dated October 11,2016. H-P/
Kumar previously conducted a preliminary subsoil study for design of foundations at the site and
presented our findings in a report dated November 9, 2016, Project No. 16-7-508.
The proposed construction is similar to that discussed in our previous report. Two similar
residences are planned on the two lots. The buildings will be 2 and 3 story wood frame
structures over walkout basement levels. Ground floors will mainly be slab-on-grade.
Excavation will be relatively extensive with cut depths up to about 20 feet on the upslope,
northern sides. If conditions are different than described, we should be contacted to review our
recommendations. •
The soils encountered at the site consisted of slightly silty sandy gravel and cobbles with
boulders that extended down to the maximum depths explored of 4 feet where digging refusal on
boulders occurred. No free water was encountered in the pits when dug in October 2016. Based
on our experience in the area, we expect groundwater level is on the order of 20 feet or deeper.
It should be feasible to cut excavation slopes up to about 15 deep at a grade no steeper than 1
(horizontal)to 1 (vertical) for a temporary condition. The excavation should be made,the
foundation walls constructed and backfilled in a timely manner limiting the time the slopes are
exposed. Surface water runoff above the cut slopes should be diverted away from the slopes to
prevent erosion and possible slope instability. There could be some rockfall of cobbles and
boulders from the excavation cut faces. Loose cobbles and boulders in the cut faces should be
removed to reduce the risks of rocks falling from the cut faces. It may be desirable to place steel
Crestone Building Company
March 6, 2017
Page 2
netting over the cut faces to help further reduce the risk of rockfall from the cut faces. The cross
section A-5:1 of Lot l provided to us shows a final slope grade of about 1I-I to 1V at the wood
deck and it appears a structural retaining wall will be needed instead of the soil graded slope.
We should observe the excavations as they progress to determine if the soil conditions are as
assumed by us or if flatter temporary cut slope grades and/or shoring are needed. The excavation
cut slopes should be observed on a regular basis after excavation and during construction by
qualified personnel, such as by us and/or the excavation subcontractor's responsible person. If
signs of slope instability are observed,we should be contacted to review the slope conditions and
make additional recommendations as needed.
A formal slope stability analyses of the hillside was not performed for the proposed relatively
shallow cut depths and our opinions and recommendations are based on the previous subsoil
conditions encountered at the site and our experience in the area. It is possible the data obtained
by deeper subsurface exploration or building excavation could change the recommendations
presented in this report. We should be advised of any variations encountered in the excavation
conditions for possible changes to recommendations contained in this report. The potential for
rockfall hazard from areas upslope of the subject lots are beyond the scope of this report.
Other recommendations provided in our previous report that are applicable should also be
observed.
If you have any questions or need further assistance, please call our office.
Sincerely,
H-Pt KUMAR
VI. 011...••U
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David A. Young, P.E. 0 32-216
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Rev. by: SLP 444101V 0. 01 e�,1,'
DAY/kac
cc: Schmueser Gordon Meyer- Anthony Alfini (anthonya@sgm-inc.com)
H-PtKUMAR
Project No. 16-7-508.A