Characteristics and formation mechanism of Jurassic variegated mudstone in the southern Ordos Basin

There are Jurassic variegated mudstones in the Xunyao mining area on the southern margin of the Ordos Basin. These mudstones were loose and easily disintegrated in water, affecting the construction of coal mines seriously and threatening the safe production of mines. This made research on the microstructure and mechanical characteristics of the mudstones significant. In this study, the XRD and SEM technic were used to analyze the composition and microstructure changes of the mudstones. The collapse and swelling tests were conducted to investigate the macro variegated shale disintegration and expansion characteristics. The results showed that the composition of the Jurassic variegated mudstone was dominated by quartz, illite and kaolinite. The original structure was relatively stable, but the microstructure changed and a large number of micro-cracks were formed after water contact. The disintegration rate of the mudstone could reach 98% within 4 min after water contact, which belonged to a highly disintegratable rock and had a good expansion performance. The localized variegated mudstone in the mining area could be caused by the change of stratum sedimentary environment. This could be induced by the water turbulence and the weathering after sedimentation based on elemental and sedimentary environment analysis. As revealing the material source of the mud-sand collapse disaster in the mining face of the Zhaojin Coal Mine in the mining area, this study provided a basis for the further research of roof characteristics in the disaster prevention and control.