Strength and deformation of rocks under freezing condition and their fracture mechanism

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Uniaxial compression tests and Brazilian tests were carried out to clarify mechanical behaviors and fracture mechanism of rocks under freezing condition. Effect of water content on strength and deformation was investigated and fracture process of the frozen rock was elucidated based on deformation behaviors and AE activities. Effects of temperature and loading rate on strength and deformation were also examined. Experimental results were discussed on the basis of an inclusion model considering mechanical role of ice within the rock. Main results are as follows.(1) At dry condition, micro-fracturing increased exponentially just before strength failure and brittle rupture was observed. At water saturated condition, specimen deformed elastically up to high stress level and occurrence of micro-fracture increased at a constant rate prior to strength failure.(2) Strength, critical strain and Poisson's ratio increased with increase in water content at -20 degrees C. Strength increased, but critical strain, Young's modulus and Poisson's ratio were not changed with rise in temperature between -5 degree C and -20 degree C. Strength increased with loading rate, at -20 degree C, but critical strain, Young's modulus and Poisson's ratio were not affected by loading rate.(3) Based on the inclusion mode], it was found that stress concentration near the tip of crack is reduced if Young's modulus of ice increases Young's modulus of ice was cleared to increase with drop in temperature or increase in loading rate through previous studies. Strength of frozen rock can be estimated to increases with drop in temperature or increase in loading rate because stress at fracture initiation increase with them.