ABSTRACT: The need for ground support that is resistant to dynamic loading becomes increasingly important as mines create excavations within higher rock stresses at greater depths. Previous impact load testing has been used to qualitatively assess the performance of different surface support and reinforcement systems. A new facility has recently been established by the WA School of Mines for dynamic testing and quantifying the performance of reinforcement systems. This test facility will be enhanced to enable dynamic testing of ground support schemes. Software to simulate the enhanced testing facility is being developed to assist with the analysis and interpretation of the data obtained for the response to impact loading of various configurations of shotcrete layers restrained by different reinforcement systems. Yield line theory is used to model the behaviour of the shotcrete layer. The simulation uses non linear responses for both the shotcrete and reinforcement systems. The simulations predict that either the shotcrete or reinforcement may fail. Reinforcement systems with high energy absorption capacities are predicted not to fail. This behaviour is consistent with the current practice in many mines where wire mesh, restrained by high energy absorption rock bolts, is placed over the previously sprayed shotcrete layer.
Currently, many mines throughout the world are placing large volumes of shotcrete and using large numbers of reinforcement systems in an attempt to control rock mass behaviour following failure due to the high stresses exceeding the rock strength in deep mines. In some circumstances, greater volumes of shotcrete and larger numbers of bolts are used than are necessary due to the uncertainty of the performance of the ground support scheme when subjected to dynamic loading.
Over the years, many physical tests involving impact of a dropped mass have been performed on surface support systems such as mesh and shotcrete and various reinforcement systems (e.g. [1, 2, 3]). In most instances, only qualitative information on the extent of ground support damage has been recorded and related to the impact energy used for dynamic loading. More recently, a new facility for dynamic testing of reinforcement and support systems has been constructed in Kalgoorlie by the Curtin University of Technology, Western Australian School of Mines. A comprehensive description of this facility is given in . This facility differs in several regards compared with previous testing facilities. Firstly, it uses a different form of loading involving the controlled transfer of momentum from a loading mass to the reinforcement system. Secondly, the facility has instrumentation to measure the behaviour of all of the components involved in a test and software to analyse this data. Finally, software based on established principles of mechanics and materials? behaviour has been developed to simulate tests.
A review of the status of the WASM Dynamic Test Facility in regard to reinforcement system testing is given prior to describing in brief the proposed next stage of development that will allow for testing of surface support systems and ground support schemes comprising surface support restrained by reinforcement. The principles of attempting to simulate this next stage of development are described. Examples are given for different types of shotcrete layers restrained by different types of reinforcement systems subjected to impact loading.