Grouting reinforcement is an effective method for controlling fractured rock in the deeply buried roadways of coal mines. However, quantitatively evaluating the strength of grouted rock masses remains a challenge. The design of grouting reinforcement is primarily based on empirical knowledge. Consequently, this study proposes a real-time in-situ method for evaluating grouting quality using measure while drilling (MWD) based on a roofbolter. Initially, we validated the method through a numerical study using the discrete element method. Several 3D rock samples with varying crack densities were established and drilled numerically, demonstrating that the strength of fractured rock masses can be better estimated using the rock drillability index rather than drilling specific energy. Therefore, a model, known as the Pd–Rc model, was established to estimate rock strength based on the rock drillability index. Subsequently, an in-situ validation was conducted using a self-developed MWD testing system to assess the grouting quality in fractured rock masses. The results show that the strength of the rock mass increases by 38%, 56.0%, and 49.7%, respectively, after grouting, as observed in three boreholes. This method allows for quantitative estimation of grouting quality.
The support of roadways in soft coal seams is a challenge in deep coal mines. For gas-rich coal seams, many methods are developed to drain the gas before mining. The penetrating hydraulic reaming (PHR) is one of the most efficient methods to reduce the gas content and pressure in the coal seams. However, the PHR method will cause many large holes in the coal seam, which brings difficulty to in-seam roadways control. The strength parameters of the coal are essential for roadway stability analysis. However, in soft coal seams, the sampling of the coal is difficult, and the direct evaluation of the coal strength parameters is unfeasible. In the present research, the surrounding rock damage characteristics of the holes induced by PHR are first evaluated by ground-penetrating radar (GPR). Then, the strength parameters of the coal are determined via the back-analysis method. After that, the deformation and failure of the roadway are analyzed, and an optimized support scheme is proposed. According to the monitored displacement and measured damage zone of the roadway, the roadway is well controlled by the proposed support scheme.
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