Abstract:

The siliceous and colloidal sandstone is common in Helan Mountains Rock Painting and Yungang Grottoes. The weighing test, ultrasonic test and uniaxial compression test were conducted on the rock subjected to freeze-thaw cycles at different temperature change rates to investigate the influences of temperature change rate on the physical and mechanical properties. The evolution and internal mechanism of crack propagation in rock after freeze-thaw cycles at different temperature change rates were revealed based on the features of acoustic emission and microseism during uniaxial compression loading process. As the temperature change rate increases, the micro-cracks increase and the joint force between particles decreases gradually, resulting in the lower peak strength and elastic modulus. Thus, the failure strain and damage parameters D_e、and  D_v  increase with the increase of temperature change rate.  During the loading process of rock, the micro-crack propagation progress shows an ‘initial compaction–propagation incubation–rapid propagation’ evolution feature, while the macro-crack propagation progress can be divided into two stages as ‘uniform propagation–rapid propagation’. And the rapid growth stage of the macro-crack also shows the wave-like development characteristic of ‘incubation–propagation–incubation–propagation’. The micro-crack and macro-crack propagation rate during the loading process increases with the temperature change rate. It is easier for micro-crack and macro-crack to enter each rapid propagation stage at a larger temperature change rate. When the temperature change rate increases to a certain value, the micro-crack and macro-crack propagate at a high rate from the beginning of loading progress to the failure of rock sample. The damage parameters  D_e and  D_v have a good fitting relationship with the relative growth rate of acoustic emission ring down count during the propagation incubation stage and the whole loading process for micro-crack, and the relative length and relative growth rate of microseism ring down count in the uniform propagation stage for macro-crack. These variables can be used to reflect the initial damage of rock induced by freeze-thaw cycles. The frost heaving force increases with the increase of temperature change rate, resulting in the different initial damage of frozen-thawed rock at different temperature change rates. It is the internal mechanism leading to the significant difference in crack propagation, acoustic emission feature and micro-seismic feature of frozen-thawed rocks during uniaxial compression loading process.

Key words: freeze-thaw cycle, temperature change rate, mechanics feature, acoustic emission, microseism