HomeMy WebLinkAboutFinal Rockfall Mitigation Agreementmog X
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November 11, 2013
Town of Vail
Attn: George Ruther
75 South Frontage Road West
Vail, Colorado 81657
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Job No. 1019 3 1 OC
Subject: Review of Rockfall Mitigation Concept 4 - Outcrop Stabilization, Vail Timber
Ridge Redevelopment Project, 1280 North Frontage Road West, Vail,
Colorado
Dear Mr. Ruther:
As requested, we have reviewed our previous rockfall risk and mitigation assessments for
the Vail Timber Ridge Redevelopment project. The project site is shown on Figure 1.
Our review also included a site visit on November 8, 2013 to observe current field
conditions. The purpose of our review was to evaluate if rock outcrop stabilization
appears to be a feasible method of reducing the potential rockfall risk to the currently
proposed redevelopment project. Our previous assessments pertaining to rockfall at the
redevelopment site are included in the references at the end of this report. This report
surnn-iarizes our review and presents our findings.
Summary of Findings: Rock outcrop stabilization appears to be a feasible method of
risk reduction. Our preliminary cost estimate for the outcrop stabilization concept is
around $700,000. This preliminary cost estimate should be reevaluated as part of the
preliminary design of the outcrop stabilization. The design and installation of the outcrop
stabilization should be done by a specialty, design -build contractor experienced in this
rnethod of rockfall risk reduction.
Proposed Redevelopment and Rockfall Risk: The currently proposed redevelopment
site cover about 5.2 acres as shown on Figures I and 2. The current plan is to raze the
existing apartment buildings and construct four new apartment buildings. The
redevelopment site and other existing buildings in the area are exposed to a rockfall risk
from potential unstable rock outcrops up slope of the project site, see Figure 2. The
likelihood that a future rockfall will reach the redevelopment site is difficult to assess
N�03-841 71 P)
Town of Vail
November 11, 2013
Page 2
with a high level of confidence. It seems reasonable to infer that future rockfall will
likely be infrequent. It is possible that a future rockfall will not occur during a reasonable
exposure time for the redevelopment. However, if a rockfall were to reach the
redevelopment site it has the potential to cause severe building damage and could cause
harm to the building occupants.
Previous Assessments: Hepworth- Pawlak Geotechnical has consulted on the rockfall
risk for the proposed redevelopment project and our most recent consultation was in April
2010. Reports describing our previous assessments are included in the references at the
end of this report. Five rockfall risk mitigations concepts were developed during our
previous assessments. They consisted of rockfall barriers (Option 1, 2, 3 and 5) at various
locations between the potentially unstable rock outcrop and the project site. Option 4 was
stabilization of the potentially unstable rock outcrops. It is our understanding that the
Town of Vail plans to use Option 4, outcrop stabilization to reduce the potential rockfall
risk.
Outcrop Stabilization: The approximate extent of potentially unstable rock outcrops
that have the potential for producing future rockfall that may reach the proposed
redevelopment site is shown on Figure 2. The length of the area requiring stabilization is
around 1,100 feet and the vertical height is up to about 90 feet. Design and installation of
the outcrop stabilization should be done by a specialty, design -build contractor
experienced in this method of rockfall risk reduction. The stabilization will likely include
a combination of (1) anchored steel- wire -mesh placed over the potentially unstable
outcrops and (2) individual rock block stabilization with rock anchors. Access to the
potentially unstable outcrops may require a helicopter.
Limitations: This review was conducted according to generally accepted engineering
geology and geotechnical engineering principles and practices in this area, at this time.
We make no warranty either express or implied. The findings submitted in this report are
based on our site visit on November S, 2013, our previous assessments for the project and
our experience with rockfall mitigation. This report has been prepared exclusively for our
client to assess if rock outcrop stabilization (Option 4) appears to be a feasible method for
reducing the potential rockfall risk to the currently proposed redevelopment project.
Information presented in this review applies only for the proposed redevelopment area
shown on Figure 2. Assessment of rockfall outside the currently proposed redevelopment
site is beyond the scope of this review. We are not responsible for technical
interpretations by others of our information. Design and installation of the outcrop
Job No. 109 3 10C
Town of Vail
Novernber 11, 2013
Page 3
stabilization should be done by a specialty, design-build contractor experienced in this
method of ro,ckfall risk reduction.
If You have questions or need further assistance, please contact us.
Respectfully Subi-nitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Ralph G. 1'ock
Engineering Geologist
And by:
Steven L. Pawlak, P.E.
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Attachrnents: Figure I - Project Site Location
Figure 2 - Potential Unstable Rock Outcrops
cc: Alpine Engineering — Gary Brooks (brqL)k�S( C ivil c Orr1 _)
Rick Pylman QJC14 pyhpqpng') 111)
REFERENCES
Hepworth-Pawlak Geotechnical, 2009, Geologie Site Assessinent and Prelinfinary
Rocltiftjll Risk and Mitigation Study, fail imber Ridge Redevelopinent 11rqject,
1280 North frontage Road West, 11'ail, Colorado. Prepared for Vail Timber
Ridge, Denver, Colorado (Job No 109 31 OB, December 17, 20019).
Hepworth-Pa wlak Geotechnical, 201 Oa, Rocl�/all Mitigation A Iternative Selection
lqfb•ination, 1'roposed Vail Tiniber Ridge Redevelopment Prqject, 1280 North
frontage Road [Fest, Hail, Colorado: Prepared for Town of Vail, Vail, Colorado
(Job No 109 31 OC, February 26, 2010).
Job Nay. 109 31 OC
Gk°�ortech
Town of Vail
November 11, 2013
Page 4
Hepworth - Pawlak Geotechnical, 2010b, March 30, 2010 Meeting, Rockfall Mitigation
Alternative Selection, Proposed Vail Timber Ridge Redevelopment Project, 1280
North Frontage Road West, Vail, Colorado: Prepared for Town of Vail, Vail,
Colorado (Job No 109 310C, March 31, 2010).
Hepworth - Pawlak GeotechnicaI, 2010c, Additional Rockfall Simulation Modeling,
Conceptual Rockfall Mitigation, Proposed Vail Timber Ridge Redevelopment
Project, 1280 North Frontage Road West, Vail, Colorado: Prepared for Town of
Vail, Vail, Colorado (Job No 109 310C, April 23, 2010).
Job No. 109 31 OC t-1
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