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| Thawing and softening behaviors and underlying damage mechanisms of frozen quartz sandstone under microwave irradiation |
| JIA Hailiang1，HAN Li1，SUN Qiang2，DONG Yuanhong3，JIN Long4 |
(1. College of Architecture and Civil Engineering，Xi¢an University of Science and Technology，Xi¢an，Shaanxi 710054，China；2. College of Geology and Environment，Xi¢an University of Science and Technology，Xi¢an，Shaanxi 710054，China；
3. College of Civil Engineering，Xijing University，Xi¢an，Shaanxi 710199，China；
4. CCCC First Highway Consultants Co.，Ltd.，Xi¢an，Shaanxi 710075，China) |
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Abstract The strength and hardness of frozen rock are several times higher than those of rock at room temperature，which leads to high excavation cost and low excavation efficiency of frozen rock layers. A new idea of employing microwave irradiation as an assisted method in excavation of frozen rock strata was proposed，which does not depend on whether the rock contains absorbing minerals and can be applied in a wide range of strata. In this paper，the quartz sandstone，which does not contain absorbing minerals，was used to explore the law of thermal melting and softening behaviors of frozen rocks under microwave irradiation. The underlying damage mechanisms were discussed and summarized based on the observation of the mesopore structure of samples before and after microwave irradiation. The results show that：(1) thawing of frozen sandstone has three stages under microwave irradiation，including rapid melting of pore ice，intense vaporization of melt water and sample drying，(2) microwave irradiation has a significant softening effect on frozen sandstone，and the strength of frozen sandstone after microwave irradiation decreases to one-fifth of that before the irradiation，and (3) the softening of saturated frozen sandstone under microwave irradiation is primarily caused by vaporization expansion effect and thermal expansion effect. The vaporization expansion effect causes the propagation of intergranular cracks，while the thermal expansion effect may induce trans-granular cracking. This study provides theoretical and experimental support for microwave-assisted breakage of frozen rock.
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2021, Vol. 40 
