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The dynamics of stress, deformation and pore pressure in the surrounding strata of underground mines are of fundamental importance to groundwater and gas emission management. Compared to numerous studies on the overlying strata, there are significantly fewer investigations concerning the underlying strata, particularly involving large-scale field monitoring. This paper presents a comprehensive field monitoring study conducted at two longwall panels with a depth of around 800 m and an inclination angle of 21°. The monitoring program focused on the floor strata within 50 m below the mining operation, but also covered the roof strata close to the longwall roadway. The purpose was to characterise the favourable zone for gas extraction from the floor coal seams. A combination of stressmeters, extensometers and piezometers were deployed and installed underground. The monitored results demonstrated that the stress change exhibited a three-stage variation—increase, decrease and recovery—during which the strata deformed and the pore pressure changed correspondingly. Strata expansion in the floor occurred primarily in the region 0–35 m behind the longwall face and vertically to at least 42 m below. Some predictive methods of the depth of the failure zone used in shallow mines were analysed to determine if they were still applicable for mining at a depth of around 800 m. [ABSTRACT FROM AUTHOR]

The variable nature of the coalmine roof poses a challenge to roadway stability during underground coal mining. There have been fatalities and financial losses in the coal mining industry due to roadway failures and roof falls. Generally, the geotechnical and geological data gathered from exploration boreholes, which are drilled at considerable distances from each other, are used to characterize the thickness and quality (including strength) of the coalmine roof. This process provides a limited number of samples that cannot represent the discontinuous nature of the strata in the coalmine roof nor can they form reliable inputs to a digital model of the rock mass component of the digital mine. Gaining confidence in the strata properties of the coalmine roof is necessary for the modelling, design, and maintenance of roadways. The paper describes the progress of the ongoing work to investigate the monitoring while drilling (MWD) concept for characterizing coalmine roofs. Large-scale drilling experiments in synthesized sandwiched rock samples without interfaces were carried out. The drilling response data were analyzed to identify whether the drill data differentiates the various strengths associated with the rock samples. The initial results show that the drilling data can differentiate the synthesized rock samples. [ABSTRACT FROM AUTHOR]