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HomeMy WebLinkAboutTimber Ridge Rockfall Mitigation Conceptual 042310� t�E�Ch 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 - ........................................................................ - ADDITIONAL ROCKFALL MITIGATION OPTION ............................................... - 1- ROCKFALL SIMULATON MODELING .................................................................. - 2 - LIMITATIONS - - .......................................................................................................... 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 i� i� ��^ �� 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 � Ge Ptech � I� -2- 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. ,; . Job No. 109 310C � C�tech i� �� � . �. � a M � � �a , � MM . -3- 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. �:� �'t;^� �;� `� � ��'`e � .� �ALS'`�L � r ,v' � ����.�;*.w.w�- p � • Ralph G. Mock Engineering Geologist And by: Steven L. Pawlak, P RGM/ksw � . �� � �! � ���f' �� y/Z7/, �,��', �, . ?�+� m °'Q}1i}i�.�o� � rfe�w��� nA�. 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). 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