Influence of fault gouge parameters on the strength behaviour of rocks of Indian coal measures formations through microstructural and laboratory investigations

This study investigated the influence of key fault-related parameters such as thickness, inclination angle, water, and clay content on the unconfined compressive strength (UCS). Fault gouge/infill materials collected from four Indian open-pit coal mines were analyzed using XRD and SEM to determine their mineral composition and microstructural characteristics. Due to field constraints in sampling adequate fault samples, synthetic reconstituted samples were developed for further investigation of strength properties. XRD results showed dominant clay minerals, with kaolinite (27.7%) in Mine-A and illite (29%) in Mine-B. SEM-based fractal dimension analysis across different microscopic scales revealed significant microstructural variability. Mine-B exhibited the highest fractal dimension, indicating intense grain fragmentation, while Mine-C and Mine-D, dominated by muscovite (29.7%) and orthoclase (51%), showed lower values, suggesting coarser particles and less fragmentation. A total of 146 samples were tested to evaluate UCS under varying fault conditions. The results indicated UCS reductions of up to 46%, 63%, 60%, and 59% with increasing fault thickness, water content, clay content, and inclination angle, respectively. Statistical analyzing through multiple linear regression and sensitivity analysis confirmed that water and clay content are the most influential factors affecting UCS, emphasizing their critical role in geomechanical stability.