升温和降温对无约束花岗岩热破裂的影响

温度变化会引起岩石内部矿物颗粒膨胀(收缩)不均匀,发生热破裂。温度变化有温度升高和降低两种作用方式,本文通过无约束花岗岩在升温和降温两种温度作用方式下的热破裂声发射实验研究,得到如下结论:(1)花岗岩升温过程中热破裂主要表现为中高温弹塑性破裂;降温过程中热破裂主要表现为中低温脆性破裂;(2)升、降温过程岩石的热破裂机理不同,升温过程主要为压缩热应力集中形成的压剪破裂,降温过程主要为局部拉应力集中造成的拉剪破坏;(3)根据声发射特征参数统计分析,同等温度范围内,岩石降温过程的热破裂声发射事件频度和强度均高于升温过程,约为2倍,降温过程的热破裂比升温过程剧烈。

Effect of Heating and Cooling on Thermal Cracking of Granite under Unconstrained Conditions

Temperature variation can cause uneven expansion(contraction) of mineral particles and result in thermal cracking in the rock. Temperature mode exposed to rock can be divided into two types: heating and cooling. According to acoustic emission monitoring of thermally induced granite in the heating and cooling process subjected to unconstrained conditions, the results indicate that: I) In the heating process, granite mainly exhibits elasto-plastic fracture in middle-high temperature. In the cooling process, thermal fracture of granite is dominated by brittle fracture in middle-low temperature. II) Thermal cracking mechanism is different between heating and cooling mode. In the heating process, thermal cracking mainly represents compression-shear mode induced by concentration of thermally compressive stress. In the cooling process, thermal cracking mainly performs tension-shear mode formed by local tensile stress concentration. III) By statistic analysis of acoustic emission data, the frequency and intensity of acoustic emission in the cooling process are higher than that in the heating process. In addition, thermal cracking in the cooling process is much more active than that in the heating process.