HomeMy WebLinkAboutTimber Ridge Rockfall Mitigation Conceptual 042310�
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HEPWORTH - PAWLAK GEOTECHNICAL
Hepwortih-Pawlak Geotechnical, Inc.
5020 Counry Road 154
Glenwood Springs, Colorado 81601
Phone:970-945-7988
Fax:970-945-8454
emaiL• hpgeo@hpgeotech.com
ADDITIONAL ROCKFALL SIMULATION MODELING
CONCEPTUAL ROCKFALL MITIGATION
VAIL TIMBER RIDGE REDEVELOPMENT PROJECT
1280 NORTH FRONTAGE ROAD WEST
VAIL, COLORADO
JOB NO. 109 310C
APRIL 23, 2010
PREPARED FOR:
TOWN OF VAIL
ATTN: GEORGE RUTHER
75 SOUTH FRONTAGE ROAD WEST
VAIL COLORADO 81657
Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthorne 970-468-1989
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY -
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ADDITIONAL ROCKFALL MITIGATION OPTION ............................................... - 1-
ROCKFALL SIMULATON MODELING .................................................................. - 2 -
LIMITATIONS - -
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REFERENCE............................................................................................................. - 3 -
FIGURE 1- PROJECT SITE LOCATION
FIGURE 2- CRSP PROFILES LOCATIONS
FIGURE 3- PROPOSED ROCKFALL MITIGATION OPTIONS PROFILE 1
FIGURE 4- PROPOSED ROCKFALL MITIGATION OPTIONS PROFILE 2
FIGURE 5- PROPOSED ROCKFALL MITIGATION OPTIONS PROFILE 3
FIGURE 6- CRSP PROFILE 1- OPTION A
FIGURE 7- CRSP PROFILE 1- OPTIONS B AND C
FIGURE 8- CRSP PROFILE 2- OPTION A
FIGURE 9- CRSP PROFILE 2- OPTION B1
FIGURE 10 - CRSP PROFILE 2- OPTION B2
FIGURE 11 - CRSP PROFILE 3- OPTION A
FIGURE 12 - CRSP PROFILE 3- OPTION B
TABLE 1- SUMMARY OF CRSP ANALYSIS AT 90 PERCENT PROBABILITY
LEVEL
TABLE 2- SUMMARY OF CRSP ANALYSIS AT 98 PERCENT PROBABILITY
LEVEL
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PURPOSE AND SCOPE OF STUDY
This report presents the fmdings of additional rockfall simulation modeling for rockfall
mitigation at the Vail Timber Ridge Redevelopment Project. The project site is located at
1280 North Frontage Road West, Vail, Colorado as shown on Figure 1. The purpose of
our simulation modeling was to provide additional rockfall dynamics information for
feasibility evaluations of rockfall mitigation for the redevelopment project. Our study is
an extension of our January 28, 2010 proposal to Town of Vail.
The rockfall dynamics modeling presented in this report is for a fifth mitigation option in
addition to the four mitigation options discussed in our December 2009 study (Hepworth-
Pawlak Geotechnical, 2009). The Colorado Rockfall Simulation Program (CRSP Version
4.0) was used for the additional modeling. This report presents the results of the
modeling.
ADDITIONAL ROCKFALL MITIGATION OPTION
w� The town of Vail is evaluating the feasibility of rockfall mitigation to protect the
�� proposed redevelopment project. The rockfall risk to the proposed redevelopment project
�� was described in our December 2009 study (Hepworth-Pawlak Geotechnical, 2009). Our
� 2009 study identiiied four conceptual rockfall mitigations options. These four options
'' would not require modifications to the existing Lions Ridge Loop. The rockfall
simulation modeling presented in this report is a fifth option that would require some
modifications to the road. It is our understanding that these modifications may be
' acceptable to the Town of Vail if the fifth option is feasible as mitigation.
' The fifth option would use rockfall net barriers with tree screens as shown on Figures 3, 4
and 5. The profiles shown on these three figures are the same profiles used in our
December 2009 study (Hepworth-Pawlak Geotechnical, 2009). The profile locations are
shown on Figure 2. Our December 2009 report may be referred to for information on the
project area geology and the original four rockfall mitigation options (Hepworth-Pawlak
Geotechnical, 2009). The rockfall nets for Option A are located along the north side of
Job No. 109 310C
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the existing Lions Ridge Loop road. The existing road will remain at its current grade
and width. Option A will require MSE retaining walls along the north side of the existing
road. The rockfall nets for Option B are located to the south of a new one-way road. The
new one-way road will be located on a fill about five feet above the existing road. The
rockfall nets with Option C will be located to the north of the one-way road in areas
where Option B will require unusually high rockfall nets, see Figure 3. Option C is only
applicable to the eastern part of the project where high existing road cuts are not present.
ROCKFALL SIMULATON MODELING
The Colorado Rockfall Simulation Program (CRSP Version 4.0) was used to evaluate
v rockfall dynamics for mitigation Options A, B and C, see Figures 3, 4 and 5. CRSP
,� Version 4.0 is a rockfall computer program that simulates rocks tumbling down a slope
i�. and predicts the statistical probability distribution of velocity, bounce height and kinetic
energy. The program takes into account slope profile, rebound and frictional
characteristics of the slope and rotational energy of the rocks. The program is a tool
,� commonly used in analyzing and mitigating rockfall hazards.
�� The design rockfall used in the CRSP models was a spherical rock with a diameter of 6.6
� feet and a weight of 12.4 tons. This is the average value of our field measurements plus
� one standard deviation. Model coefficients used for this study are the same calibration
used in our December 2009 models (Hepworth-Pawlak Geotechnical, 2009). Three
topographic profiles were evaluated. Locations of the profiles are shown on Figure 2 and
the profiles are presented on Figures 6 through 12. These are the same profiles used in our
December 2009 models (Hepworth-Pawlak Geotechnical, 2009). Results of the
simulation models are presented on Table 1 for the 90 percent probability level and on
Table 2 for the 98 percent probability level. The 90 percent probability level means that
there is a 10 percent chance that the model values will be exceeded and the 98 percent
probability level means that there is a 2 percent chance that the model values will be
exceeded. The choice of probability level for mitigation will depend on the degree of risk
acceptable to the owner and governmental regulatory agencies.
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Job No. 109 310C
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LIMITATIONS
This study was conducted according to generally accepted geotechnical engineering
principles and practices in this area, at this time. We make no warranty either express or
implied. The information submitted in this report is based on our previous studies of the
project site and rockfall simulation modeling along the three profiles presented in this
report. This report has been prepared exclusively for our client to evaluate the feasibility
of the conceptual rockfall mitigations options discussed in this report. We are not
responsible for technical interpretations by others of our information. Additional rockfall
analysis should be performed when the specific development and mitigation plans have
been determined.
If there are questions or if we may be of further service, please call our office.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
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Ralph G. Mock
Engineering Geologist
And by:
Steven L. Pawlak, P
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cc: Alpine Engineering��n Palmer (palmer e al�inecivil.com)
Rick Pylman (rick �ylman.com)
REFERENCE
�' Hepworth-Pawlak Geotechnical, 2009, Geologic Site Assessment and Preliminary
Rockfall Risk and Mitigation Study, Vail Timber Ridge Redevelopment Project,
1280 North Frontage Road West, Vail, Colorado: Prepared for Vail Timber
� Ridge LLC, Denver, Colorado (Job No. 109 310B, December 18, 2009).
Job No. 109 310C
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109 310C �C�t@C�'1 Figure 1
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