Justin Pentz

Date of Graduation

2014

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John D Quaranta

Committee Co-Chair

Hema Siriwardane

Committee Member

John P Zaniewski

Abstract

In this report investigation and identification of the elements of bench cut bedrock slopes that affect the rockfall characteristics was performed in order to create alternatives for highway bedrock cut slope design for the state of West Virginia. The scope of this research was to determine what geometric and material parameters effect rockfall on bench cut bedrock slopes and present design suggestions for increasing rockfall retention. Additionally as a means developing alternative slope designs a new design methodology involving slope stability and rockfall behavior was established.;In order to analyze rockfall behavior in West Virginia geology, a three dimensional version of Colorado Rockfall Simulation Program (CRSP-3D) was selected to provide rockfall simulation. A field calibration workbook was developed in order to provide a systematic procedure for selecting and evaluating field sites as candidates for calibration of the rockfall modeling software. Using the data collected, the program was calibrated for two principal types of rockfall. These groups, Hard and Soft Rock, were defined to be directly correlated to preexisting West Virginia Design Directive 403 (WVDOH DD-403) rock classifications.;A parametric sensitivity analysis was conducted using WVDOH DD-403 geometric parameters for bench cut bedrock cut slopes. Using Oregon Department of Transportation specifications as a guideline, a threshold of ninety percent on-slope rockfall retention was imposed as a pass-fail criterion. Parametric analysis showed that if all benches located in a profile are designed as the primary means of rockfall catchment, benches widths should be designed to a minimum of 35 feet in order to provide adequate on slope catchment. As an attempt to increase rockfall retention, an alternate toe of slope geometry to that specified in the WVDOH DD-403 was implemented to the same parametric trails previously conducted. A Rockfall Catchment Area Design (RCAD) ditch was selected due to its widespread use by other state agencies. Results from modeling showed in the majority of iterations, the RCAD ditch was necessary in order to provide acceptable retention for the entire range of the slope parameters. Although the RCAD ditch equals or increases rockfall retention to the WVDOH toe of slope design in all cases, it did not yield total rockfall retention to the ninety percent threshold for all geometric profiles analyzed. Therefore, RCAD ditches should not be considered a complete design solution for toe of slope rockfall retention during profile design; other geometric parameters must be considered in order to facilitate a profile meeting rockfall retention requirements.;In order to assess the rockfall behavior of alternative geometric profiles to those currently specified by the WVDOH, a design methodology was developed for analyzing the effects of cut slope stability and the resulting rockfall retention. This process incorporated numerical stability modeling using the Hoek-Brown failure criterion coupled with General Limit Equilibrium analysis method. CRSP-3D provided rockfall analysis for each design profile. The analysis was performed on a section of U.S. 48 in Hardy County consisting primarily of hard rock material. . The results of the alternate design methodology showed that iterative reductions in the number of geotechnical benches in a slope profile can be performed as to meet stability and rockfall retention requirements, provided RCAD ditch design is diligently designed and modeled.

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