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Procedures to Develop Defined Metrics and Protocols Using Existing Rockslope and Rockfall Design Guidelines within Corridors for Mitigation of Rockfall and Rockslides

Description:

Rockfall and rock slope design engineering guidelines have been established since the 1960’s with such notable works as the Ritchie Ditch Catchment (1963), Rock Slope Engineering (Hoek and Bray, 1974), Rockfall Catchment Area Design Guide (FHWA-OR-RD-02-04), and more recently Rockfall Characterization and Control (Transportation Research Board (TRB), 2012). These guidelines offer the basis for design of rock slopes and rockfall catchment but do not establish guidelines, criteria, or metrics for implementation that designers or agencies can follow.

Given the desire to make and communicate asset management based design decisions, and to design for resilience and the consideration of life-cycle cost, there is a need to develop a rock slope and rockfall guideline metric and framework that establishes suggested parameters and protocols based on:

Rock slope evaluation to determine potential for generating rockfall by either a condition, tolerable risk, or performance based systems or combinations therein,

Rock slope mitigation options such as blasting methods, stabilization, or protection measures or combinations of each to reduce the potential for rockfall,

Ditch catchment options based on rock slope evaluation, mitigation options and traffic volumes,

Formulating an iterative life-cycle process to evaluate and encompass roadway design, constructability, environmental, cost, maintenance, and other considerations using the previous points including potential for rock slope to generate rockfall, mitigation options, and ditch catchment requirements,

Results of the research will be useful to transportation agencies charged with managing rockfall hazards.

Objective:

The objective of the research is to provide owners and designers of rock slope stabilization and rockfall sites with consistent guidelines to evaluate minimum requirements. The work is intended to provide guidance that would allow basis for actions at individual sites within a transportation corridor. A framework would be established to allow expansion to entire networks or systems of roads.

Benefits:

Currently DOT agencies have a wide range of methods or procedures from prescriptive to non-existent for evaluating rock slope blasting, rock slope mitigation, and rockfall ditch catchment within a corridor that has led to questions with performance, liability, standards and other issues between agencies, designers and practitioners. Clarification and further refinement of design procedures will provide a more functional design process with consistency among agencies.

All parties would be able to communicate consistently on the basis for design and the expectations for performance in terms of conditions, risk, resilience and life cycle cost. The value of the designs and mitigation actions with respect to the performance of a corridor would be able to be demonstrated.

Tasks:

The following tasks are necessary to achieve the stated objectives:

1. Evaluation of previous Rockfall Hazard Rating Systems (RHRS) or modified rating systems to evaluate and assess the potential for a given rock slope to generate rockfall.

2. Review various rock slope mitigation options based on rockfall potential. Slope mitigation includes such items as blasting, bolting, draped mesh, and pinned mesh.

3. Evaluate rockfall catchment relative to rock slope treatment.

4. Evaluate rockfall catchment percentage needs based on such factors as traffic volumes, roadway layouts, slope mitigation, ability to maintain, and others for a given corridor.

5. Determine performance measures and metrics for various design combinations.

6. Prepare a report detailing the results of items 1 through 5. Recommend an evaluation system to assess the condition of a rockfall system, and provide recommendations for evaluating and maintaining existing rockfall protection systems in a format suitable for adoption by AASHTO.

Implementation:

The implementation of these plans will allow the geotechnical community to provide better function of the corridor with more established design protocols and understanding of the resulting asset management impacts. Currently, there are no well-defined procedures using design guidelines for rock slope and rockfall prone corridor protection systems. The recommended practice developed as part of this research would be in a format consistent with AASHTO requirements.

Sponsoring Committee:AKG10, Engineering Geology
Research Period:12 - 24 months
Date Posted:04/27/2016
Date Modified:05/05/2016
Index Terms:Rockfalls, Rockslides, Metrics (Quantitative assessment), Guidelines, Rock slopes, Plan implementation, Life cycle analysis, Geometric design,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Design
Safety and Human Factors
Geotechnology

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