(1. State Key Laboratory of Water Resources and Hydropower Engineering Science,Wuhan University,Wuhan,Hubei 430072,
China;2. Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering,Ministry of Education,
Wuhan University,Wuhan,Hubei 430072,China)
Abstract:In this study,the alterations in the microstructures of three types of rocks (i.e. sandstone,granite and marble) were observed with the polarized light microscopy after thermal treatment at different temperatures. The variations in the physical-mechanical properties(including the longitudinal wave velocity,porosity,Young?s modulus,peak stress and the corresponding strain) of three types of rocks with the thermal treatment from room temperature to 800 ℃ were analyzed and compared and were correlated to the microstructural variations. The strong ductile behavior of the thermally cracked rocks was interpreted with a micromechanical model by taking into account the normal stiffness reduction of micro-cracks. A notable change in the carbonate cementation was observed in thermally cracked sandstone,in which the thermally induced cracking was not developed across the mineral particles. Both transgranular and intergranular cracking developed in thermally cracked granite with a maximum opening of 100 μm at 800 ℃,which was one order of magnitude larger than that at 400 ℃. The cracks in thermally treated marble were mainly intergranular,with the maximum width of about 20 μm at 600 ℃. Different from granite and marble,a dramatic decrease of elastic modulus occurred in thermally cracked sandstone when the treatment temperature was over 500 ℃,which was mainly ascribed to the phase transition of quartz. It was found that the physical-mechanical properties of the thermally cracked rocks depended much on the diagenetic processes,mineral compositions and cracking patterns. Moreover,the numerical simulation results are in good agreement with the experimental data,showing that the mechanical behaviors of the thermally cracked rocks are closely related to the density and stiffness of the thermally induced cracks.
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