Dynamic testing of ground support elements
This applied research investigation will lead to the development of practical energy absorption guidelines for the types of reinforcing systems, face restraint and surface support systems used in Western Australian mines.
The guidelines will provide quantitative data for the energy absorbed by the reinforcing and support systems or a fully-integrated ground control scheme; these data could be used by geotechnical engineers to design ground control schemes appropriate for expected rockburst conditions. An additional, but important outcome has been the development of a dynamic testing facility based in Western Australia. The facility is capable of subjecting reinforcing and support systems to standard impact loadings. The first stage of the research is being sponsored by MERIWA, Harmony, Goldfields, Geobrugg, Newmont, Placer Dome, MBT, Strata Control Systems, KCGM, WMC and DSI. Key researchers include: John R. Player (PhD Student), Alan Thompson, Ernesto Villaescusa and Brett Scott. This project is ongoing.
Dynamic testing of rock reinforcement using the momentum transfer concept Player, Villaescusa & Thompson
The West Australian mining industry has an urgent need for the construction of a local dynamic test facility that can perform repeatable dynamic loading on reinforcement systems, support systems and ground control schemes. The West Australian School of Mines, with the assistance of industry and government funding, has developed a test facility using a novel testing process. The facility is in the commissioning phase, and has been proven to enable repeatable dynamic loading of reinforcement systems. Tests have a high level of instrumentation to measure forces and displacements combined with digital video recording. Analysis of these data allow the calculation of energy absorbed from the force displacement curves of the tested system and the impact point in the facility.
The performance of reinforcement systems when subjected to dynamic loading may be substantially different to the performance measured in quasi-static tests. In order to investigate the extent of the differences in behaviour, a new testing facility has been developed to apply dynamic loads to reinforcement system specimens set up in double embedment configurations. A computer simulation of the test facility has been developed to facilitate test data processing and interpretation. The tests are monitored electronically and by high speed digital video. The results from the various forms of instrumentation are filtered and then combined and analysed. The analyses enable the energy absorption characteristics of different reinforcement systems to be characterised. An example is presented of a simulation and test on a reinforcement system. The ability to apply multiple impacts to simulate repetitive loadings from seismic events is one major asset of the testing facility.
Rock reinforcement design for overstressed rock using three dimensional numerical modeling Wiles, Villaescusa & Windsor
A procedure is presented for the design of reinforcement for highly stressed rock based on 3D numerical stress analysis using the MAP3D code. Modelling requires extensive characterisation of the rock mass strength and deformability and appropriate characterisation of the stress field. The numerical model is calibrated using a Rock Mass Damage Criterion and a Rock Mass Failure Criterion that are calibrated to ob-servations of in situ cracking. These criteria define an outer damaged or cracked zone and an inner, failed or broken zone. Examples are used to show how the extent and dimensions of these zones can be determined by post-processing the modelling results and how the boundary of these zones can be used to dimension the primary reinforcement scheme.
Threaded bar has a long history of use in civil engineering projects, particularly for long ground anchors where the ability to join shorter straight lengths is achieved using thread couplers. Threadbar is also widely used in mining applications for the control of static and dynamic loadings. Threadbar may also be referred to as rebar or Gewi bar, a proprietary product developed by Dywidag Systems many years ago.
The length of collar and toe embedment either side of a discontinuity will affect the performance of the complete system. It will also affect the amount of load and when the load is transferred to the surface hardware. This paper will examine the affect of changes in embedment length and surface fixtures on the performance of 20mm threadbar to dynamic loading. The Western Australia School of Mines (WASM) Dynamic Testing Facility (Player et al. 2004, and Player et al. 2008)) has been used to examine the performance of threadbar.
An extensive axial test program has been used to quantify the difference between the static and dynamic capacities (kN/m of embedment) for friction rock stabilisers once sliding starts. Rough simulated boreholes have been developed for the installation and dynamic testing of rock bolts at the WASM Dynamic Test Facility. The rough simulated borehole is used for rock bolts that are sensitive to equipment installation technique or borehole geometry (particularly friction rock stabilisers and resin encapsulated bolts). The 47mm split tube bolt has a 50% reduction in embedment capacity (but with significant variation) dissipating 2.7kJ/100mm of sliding per metre of embedment, and the Omega (inflatable) bolt had a 70% reduction in embedment capacity dissipating 6.2kJ/100mm of sliding per metre of embedment. The Omega bolt dynamic capacity remained at least equivalent to the split tube bolt static capacity.