高温后砂岩三轴卸荷试验研究

TRIAXIAL UNLOADING TEST OF SANDSTONE AFTER HIGH TEMPERATURE

通过三轴卸荷试验,综合考虑回弹值和纵波波速与温度的关系,对高温后砂岩的纵波波速和力学特性与温度的变化规律进行研究。试验结果表明:随着烘烤温度的升高,砂岩的纵波波速降低,且经历的温度越高,波速下降的幅度越大;随着烘烤温度的升高,砂岩的回弹值并非简单的单调递增或递减;砂岩的强度力学特性在摩擦特征和胶结特性共同作用下变化,砂岩高温烘烤后摩擦特性大大加强,在较大围压下,由于摩擦作用其强度得到显著提高;高温烘烤后纵波波速、回弹值和强度不具备必然规律;自然风干岩样在低围压下卸载破坏,依然表现出明显的压剪破坏形式,300℃,600℃,900℃烘烤岩样的轴向劈裂现象却逐渐增强;分析认为高温烘烤后岩样的抗拉强度出现了明显降低,热处理后砂岩内部产生热应力,由此诱发表面热开裂及内部微裂纹是造成抗拉强度降低的本质原因。

Comprehensively considering the relationship of the rebound value and longitudinal wave velocity with the temperature,the change laws of the longitudinal wave velocity and mechanical characteristic with temperature of the sandstone after high temperature are studied by triaxial unloading test.The test results show that：（1） The longitudinal wave velocity of the sandstone becomes lower with the increase of baking temperature.And the velocity decreases more rapidly while the temperature becomes higher.（2） With the increase of baking temperature,the rebound value of the sandstone is not a simple monotone increase/decrease.（3） The mechanical properties of sandstone change under the interaction of friction characteristics and cement properties.The friction characteristics strengthen greatly after high temperature baking;and then,the strength of sandstone increases greatly under the high confining pressure.（4） The longitudinal wave velocity,rebound value and strength don￠t have inexorable law after high temperature baking.（5） The unloading damage of natural air-dried rock samples under low confining pressure still shows a significant compression and shear failure mode.（6） By analysis of the test results,we believe that the tensile strength of rock samples decreases significantly after high temperature baking.The interior of sandstone produces the thermal stress after heat treatment.The thermal stress induces the thermal cracking of the surface and internal microcracks,which is the essential reason of the tensile strength decreasing.