Stabilization of Gob-Side Entry with an Artificial Side for Sustaining Mining Work
A concrete artificial side (AS) is introduced to stabilize a gob-side entry (GSE). To evaluate the stability of the AS, a uniaxial compression failure experiment was conducted with large and small-scale specimens. The distribution characteristics of the shear stress were obtained from a numerical simulation. Based on the failure characteristics and the variation of the shear stress, a failure criterion was determined and implemented in the strengthening method for the artificial side. In an experimental test, the distribution pattern of the maximum shear stress showed an X shape, which contributed to the failure shape of the specimen. The shear stress distribution and failure shape are induced by a combination of two sets of shear stresses, which implies that failure of the AS follows the twin shear strength theory. The use of anchor bolts, bolts, and anchor bars enhances the shear strength of the artificial side. When this side is stable, the components can constrain the lateral deformation as well as improve the internal friction angle and cohesion. When the AS is damaged, the components prevent the sliding of broken blocks along the shear failure plane and improve the residual strength of the artificial side. When reinforced with an anchor bar, the AS is still stable even after mining operations for three years.
Intelligent diagnosis of bolting systems under uncertain/dynamic impact
Abstract
This paper proposes a method to diagnose bolting systems from the acceleration response signals generated from a dynamic impact testing and simulation. It shows that the spectrum and response level have the unique features corresponding to the specific states of the bolting system which can be used to train an artificial neural network for automatic diagnosis.
Impact testing for rockbolt design in rockburst conditions
Abstract Weight-drop tests on steel rods simulating the impact loading of mechanical bolts by rock blocks ejected during rockbursts were performed in the laboratory to study the dynamic response of these bolts. The steel rods were loaded to deform either elastically or plastically. Cushions of rubber and wood and a slip mechanism were investigated as a means to reduce the elastic stress or plastic strain in steel rods. It is found that the elastic stress or the plastic strain can be determined using the energy balance approach. While the stress can be used as the controlling parameter for rockbolt design within the elastic range, the plastic strain parameter must be employed to exploit the energy absorbing potential of the bolt if plastic deformation of the bolt is acceptable. Rockbolt design examples are given to illustrate the concepts of elastic and plastic designs. It is found that soft cushions placed between mesh and head plate can be employed to absorb wave energy and protect weak connections in a rockbolt-mesh support system, effective slip mechanisms must be designed for fully grouted bolts, and frictional bolts are ideal for excavation walls. Finally, it is pointed out that if the accumulation of plastic strains is anticipated due to repeated seismic loadings, additional support elements must be installed with time.