Abstract
Underground support system using tendons has been one of the significant achievements in Civil and Mining engineering endeavours in facing challenges of ground control. However, shear failure of rock bolts is still one of the least monitored phenomenon in underground excavations with respect to seismic events. The understanding of the performance of rock bolts under dynamic loading condition requires a great deal of research. A series of tests were undertaken utilising a drop hammer mass of 600 Kg from a maximum height of 3.7 m over concrete blocks in the double shear box with chemical resin encapsulated a rock bolt to investigate the performance of rock bolts under dynamic shear load. Load cells, displacement laser and high speed camera were used to monitor the test. Results from the data analyses are presented in the form of displacement, hammer mass drop velocity, acceleration and force variation with time for all components involved in each test. The time factor was found to contribute 30 % of the shear load in static testing in comparison with dynamic; In particular, the force-displacement curve and energy absorption for the reinforcement system are presented to examine the performance of rock bolts and conclusion drawn.
Highlights
Characterisation of the strength of rock bolts and cable bolts for underground mining is generally based on tensile and shear strength
The need for effective research on ground support credibility is of equal importance to the collapse of the ground due to gas outbursts, which are more common in coal mines worldwide and are well documented
Tendon shear strength characteristics are important when shear deformation occurs across joints and shear zones, which are the weakest zones in ground structure that normally yields readily to rock burst or any other seismic activity
Summary
Characterisation of the strength of rock bolts and cable bolts for underground mining is generally based on tensile and shear strength. The Beaconsfield gold mine collapse, in Tasmania, triggered by seismic activity and pressure bursts at Austar coal mine, due to high levels of stress contribution caused by the presence of disturbed structural geology in the region with fault zones and shear zones as reported by Galvin and Hebblewhite (2016) are stark reminder of the challenges that mines are faced with in adverse conditions. This necessitates the need for credible research on ground support under these adverse conditions under both static and dynamic conditions. This paper describes the method of dynamic shear testing of tendons using double shear apparatus and compares the findings with static method
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