Ground support
The purpose of ground support is to maintain excavations safe and open for their intended lifespan.
The effectiveness of a support strategy is important for two main reasons, namely: safety to personnel and equipment and also to achieve the most economical extraction of ore. Within this context the use of the most economical and efficient process for ground support is important in order to maintain safety and to reduce operating cost.
Research papers
Understanding the complete stress-strain behavior of shotcrete is extremely important in ground support design; especially in cases where large deformations are expected such as around mine excavations at great depth. The application of non-linear numerical modeling to mining industry problems has increased in recent years. More realistic stress-strain response and failure criteria in complex plasticity models are also being used in the design of the larger, deeper mines. One of the factors to improve the reliability of numerical modeling is to properly define geotechnical parameters for both the rock mass and shotcrete surface support. Uniaxial and triaxial compression tests on steel fibre reinforced shotcrete (SFRS) have been used to quantify elastic-plastic response behaviour for both the peak and post-peak regions. The laboratory tests were conducted with a servo-controlled testing machine to obtain complete stress-strain curves. The test results include unconfined and triaxial compressive strength, shear strength and tensile strength together with the elastic and plastic mechanical properties of SFRS. A method is also suggested for obtaining the plasticity parameters for non-linear modeling of SFRS.
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Uniaxial and triaxial compression tests on steel fibre reinforced shotcrete (SFRS) have been used to quantify elastic-plastic response behaviour for both the peak and post-peak regions. The laboratory tests were conducted with a servo-controlled testing machine to obtain complete stress-strain curves. The test results include unconfined and triaxial compressive strength, shear strength and tensile strength together with the elastic and plastic mechanical properties of SFRS. A method is also suggested for obtaining the plasticity parameters for non-linear.
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In-Cycle shotcrete is an important component of support for many underground excavations in rock. In particular, the safe re-entry time after shotcrete has been sprayed needs to be considered as it influences the productivity associated with development. It is proposed that the shear strength of the shotcrete matrix is a better parameter to consider than the Uniaxial Compressive Strength of the overall shotcrete material including coarse aggregate. A number of shotcrete paste mixes were prepared and evaluated for strength gain. It was found generally that the shear strengths of shotcrete pastes increase exponentially during the first 4 to 8 hours of curing in all shotcrete mixes except when the pastes included a hydration stabiliser. It was found for shotcrete mixes with accelerator, synthetic fibres and aggregates that an average layer of about 50mm thickness develops sufficient shear strength of about 20kPa within about one hour to support a tetrahedral block with 1m edge lengths and the layer mass. For the same shotcrete layer, it was found that a cubic metre block and the shotcrete layer can be supported within about 3 hours and 50 minutes when the shotcrete shear strength is estimated to be approximately 97kPa.
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