Acoustic emission investigation of hydraulic and mechanical characteristics of muddy sandstone experienced one freeze-thaw cycle

Artificial freezing technology has been proved to be one of the most effective methods to construct deep mine shafts in water-rich soft rock in western China. Water penetration and shaft flooding accidents are always the major problems during the construction and utilization. In this paper, using triaxial seepage testing and acoustic emission (AE) monitoring, the mechanical and hydraulic characteristics of muddy sandstone specimens taken from Meilin Temple Mine at a depth of 700 m in Ordos were studied under one full freeze-thaw loading cycle. Test results showed that the cementation of rock samples is deteriorated after one freeze-thaw cycle and the maximum width of secondary fractures on surface of samples are about 0.03 mm. While the failure process of rock sample is revealed by AE energy, the variation of permeability corresponds well to AE amplitude. For confining pressure lower than 25 MPa, as the confining pressure increases, the rock tends to fail in ductile mode. AE signals are not active in the beginning loading stage under higher confining pressure, on the contrary the maximum values of AE energy and amplitude during the whole test process increase. While the peak strength increases by 64.3%, both initial permeability and peak permeability decrease obeying negative exponential law. Additionally, the crack initiation ratio demonstrates a linear relation with confining pressure; the damage ratio shows an exponential trend.