The exhaustion of coal resources near the surface forces the panels to go deeper into higher stressed and more geologically complicated environments. Implementing tougher safety regulations requires semi to full mining automation to reduce the number of underground miners. All of these changes pose greater challenges for mine operators striving to achieve high production while maintaining favourable mining conditions. Weak geological structures, such as faults and fracture zones within a longwall panel may have great impact on the stability of the coal and rock mass. The reactivation of the structures and induced fractures during mining can significantly change the rock mass integration and stress conditions in the roof and floor, and cause the roof rocks to collapse near the working face. Understanding the fault reactivation and fracture development is thus crucial for the control and prevention of impending problems. Microseismic monitoring techniques developed by CSIRO has applied to a number of longwall coal mines in Australia to monitor fault reactivation and rock fracturing ahead of mining face during production. This paper presents the microseismic techniques used for this application and results obtained at the mines. It is demonstrated that fault reactivations and rock fracturing associated with mining can be efficiently observed remotely and in real-time using an array of seismic sensors. The microseismic results provide very useful information for longwall coal mine operators for risk management and production control.
Longwall mining has become the most widely used mining method for underground coal mines due to the productivity that can be achieved. Typically, longwall panel are 100–300 m wide, 1,000–3,000 m long and 2.8–4.5 m high (coal mining height). In Australia, the depth of the coal seam being mined is typically 150–500 m below the ground surface. Along the two sides of the panel are pairs of parallel tunnels (roadways) for transportation and ventilation. At the mining face a cutting drum (shearer) moves back and forth across the panel. The roof strata of the coal seam near the face are supported by hydraulic shields which are moved forward with the progression of the mining. Behind the shields, the unsupported roof strata collapse to form what is known as the goaf (Figure 1). The trend of longwall coal mining goes to longer and wider longwall panels for more production. The exhaustion of coal resources near the surface forces the panels to go deeper into higher stressed and more geologically complicated environments. Implementing tougher safety regulations requires semi to full mining automation to reduce the number of underground miners. All of these changes pose greater challenges for mine operators striving to achieve high production while maintaining favourable mining conditions. Weak geological structures, such as faults and fracture zones within a longwall panel may have great impact on the stability of the coal and rock mass.
