Water softening effect on the creep behavior of mineral components in red shale in Kaiyang phosphate mining area, China

To get a better insight into the creep behavior of water-softening rocks, the creep behavior of minerals, mainly including quartz and chlorite, in red shale before and after water soaking was investigated by using the nanoindentation creep test. The power-law, logarithmic, and exponent functions were compared and comparison results reveal that a sequence of exponential function performs better. The one-dashpot Kelvin model, Burgers model, and two-dashpot Kelvin model were also compared and the two-dashpot Kelvin model depicts the nanoindentation creep data best. Experimental results show that the red shale is composited by the hard inclusions and the clay matrix. Water-rock interaction has no influence on the quartz while the hardness and elastic modulus of chlorite decrease significantly after water soaking for 24 h. The creep parameters, including the creep modulus and viscosity, were calculated for the chlorite before and after water soaking. The creep modulus decreases 29.75–38.24% and the viscosity decreases 13.90-97.28%, respectively. Based on the calculated the strain rate sensitivity, m, the chlorite creep is mainly dominated by dislocation but the quartz creep is dominated by both the dislocation and diffusion. After water soaking, the creep dislocation become more dominant since the strain rate sensitivity shows a decreasing trend. The findings of the present study are of great significance for the control of roadway creep deformation after excavating and exposing to wetting air.