Compressive failure response and thawing-induced softening effect of frozen ice-sandwiched rock mass
LI Qiang1，JIA Hailiang1，YANG Gengshe1，YANG Liu2，YANGY Chunmei1，LIU Xianhuan1
(1. College of Architecture and Civil Engineering，Xi?an University of Science and Technology，Xi?an，Shaanxi 710054，China；2. School of Transportation，Southeast University，Nanjing，Jiangsu 211189，China)
Abstract：With the continuous warming of climate，thermal and melting degradation of perennial frozen layers in the Qinghai-Tibet Plateau，Alps and other high altitude areas leads to a large number of rock mass instability disasters. To study the "softening effect" of mechanical properties of frozen ice-sandwiched rock mass upon thawing is a key premise to reveal the thermal melting instability mechanism of frozen rock mass. In this paper，a series of uniaxial compression tests were carried out on frozen rock mass with different crack angles and melting temperatures，and acoustic emission and high-speed photography methods were used to monitor the failure process. The results show that：(1) the uniaxial compressive strength of the samples decreases first and then increases with the increase of the crack angle θ.(2) The uniaxial compressive strength of the sample decreases gradually with the increase of temperature，which can be divided into three stages： rapid reduction stage(－20 ℃～－6 ℃)，fluctuation decline stage(－6 ℃～－1 ℃) and strength plunge stage(－1 ℃～0 ℃).(3) The samples with different crack angles have three failure modes：the ice layer is crushed as a whole，which is brittle failure；The obvious plastic deformation occurs after the ice is broken，which is ductile failure. Cracks in the middle of the ice layer extend to the upper and lower ice-rock interface，and relative slippage occurs along the interface of the upper and lower rocks. The whole sample is broken，which is brittle failure.(4) Under the condition of thermal melting，the failure mode of fractured ice-sandwich rock mass can be divided into two types：the cracks in the middle of the ice layer expands to the upper and lower ice-rock interface，the relative slip of the upper and lower rocks occurs along the interface，and the whole sample is broken(－20 ℃≤T≤－6 ℃ or －1 ℃≤T≤0 ℃)；Obvious plastic deformation occurred after the ice layer was broken，and no whole fracture occurred(－6 ℃＜T＜－1 ℃). Through theoretical analysis，the influence mechanism of crack Angle on the compressive strength of fractured ice-sandwich-rock mass is mainly that the failure mode of fractured ice-sandwich-rock mass changes from vertical splitting failure of ice sheet to shear failure along ice-rock interface and shear failure along ice layer with the increase of crack Angle. Based on the results of NMR one-dimensional imaging，the content of unfrozen water at the ice-rock interface increases continuously during the heating process，that is，the strength of the ice-rock interface decreases continuously，which leads to the temperature dependence of the strength variation of fractured ice-rock mass.
