Development of a Rockbolt Support Element for Discontinuous Deformation Analysis

Montana Technological University, Butte MT

Investigators

Abstract

CMS-0201577 PI: Mary MacLaughlin Institution: Montana Tech Title: "Development of a Rockbolt Support Element for Discontinuous Deformation Analysis" Astract: The primary objective of this research project is to develop a rockbolt support element that is capable of modeling actual rockbolt behavior, particularly nonlinear movement between the bolt and the rock which is critical for numerical modeling. Discontinuous Deformation Analysis, DDA, has several unique features that make it a perfect candidate for development of a bolt element that has the ability to characterize rockbolt behavior to a much higher degree of realism and accuracy than has previously been possible. DDA is an implicit discrete element method that already has the capacity to model "blocks" of any irregular shape, and the contact routines are specifically designed to efficiently capture contact between blocks with both convex and concave vertex angles. The method accounts for frictional, cohesive, and tensional forces which are present at the contacts, and allows blocks to slide, separate, and impact without penetrating. A rockbolt element will be implemented as a "block" with a particular geometry and special material properties consistent with those of a typical rockbolt. The support-rock interaction mechanics will then be incorporated into the model as manifested by displacement between the bolt element and the surrounding rock blocks. This capability to model bolt behavior, especially pull-out failure, will make the DDA rockbolt element a more accurate modeling tool than other previously developed numerical rockbolt support elements. Mark (2000) states that "the reinforcement mode is actually dictated to the bolts by the ground, rather than the reverse." One of the real strengths of the DDA approach is that this outcome is a natural result of the analysis. The behavior and failure mode do not have to be specified before or during the analysis - they are part of the calculated results. The NIOSH Spokane Research Laboratory, which was a branch of the US Bureau of Mines until 1995 and is now part of the National Institute for Occupational Safety and Health, has invested significant resources into the development, installation and testing of instrumented rockbolts since the mid-1980's. Analysis of the data collected using the instrumented rockbolts has contributed a great deal to the general understanding of the behavior of rockbolt supports, and collaboration with NIOSH personnel is an important component of this project. The development of the bolt element will involve bolt type selection, theoretical development, algorithm development and implementation. The PI and Ms. Kathryn Clapp, the Montana Tech graduate student involved in this project, will jointly work on all of these aspects, with assistance from Mr. Steve Signer of NIOSH. One fairly unique aspect of this project is that once the theoretical development is finished and the rockbolt algorithms have been implemented into the software, validation will be performed using the large archive of NIOSH instrumented rockbolt data which has already been collected. This is a tremendous advantage and will allow the project to be completed in a relatively short period of time, with a modest budget. Ms. Clapp will perform the bulk of the validation activities, which will entail constructing DDA models corresponding to each of the different laboratory test configurations used, and performing analyses with model conditions specified to represent the lab tests as closely as possible. The DDA calculations of the head displacement and load values at points along the bolt will be recorded and compared to actual bolt behavior as observed during the tests. Reference: Mark, C. (2000). "Design of Roof Bolt Systems." In C. Mark, D.R. Dolinar, and R. Tuchman, eds. New Technology for Coal Mine Roof Support, Proceedings of the NIOSH Open Industry Briefing, NIOSH IC 9453, pp. 111-132.