热损伤花岗岩三轴卸围压力学特性试验研究

利用岩石伺服试验系统,对经历25℃~900℃作用后的花岗岩试样进行三轴卸围压试验,研究高温后花岗岩在卸荷路径下的变形特性、参数特征及破坏形态。结果表明:经历300℃后的岩样围压卸荷量最少,最容易发生破坏。基于应变围压增量比,定量揭示了卸荷破坏是由强烈的径向变形和体积扩容所致。随着温度上升,各应变围压增量比均先增大后减小,在300℃时达到最大。卸荷过程中岩样的变形模量逐渐减小,25℃~900℃之间,减小33.20%~59.11%,且温度越高减小越多,与体积应变均呈二次多项式相关;泊松比逐渐增大,25℃~900℃之间,增大164.96%~274.03%,且温度越高增加越多,与体积应变均呈线性相关。高温后的岩样在单轴压缩下均呈轴向劈裂破坏,并存在多个贯通裂纹;在三轴压缩下为宏观单一的贯通剪切破坏形态;三轴卸围压下破坏形态则比较复杂,常温时为高角度的局部剪切破坏,随温度升高,岩样变为贯通剪切破坏,到900℃时又变为局部剪切破坏。

Experimental study on mechanical properties of thermal-damage granite rock under triaxial unloading confining pressure

The triaxial tests on post-high-temperature granite samples (25℃~900℃) under unloading confining pressure are performed to study the deformation characteristics, parameters and failure patterns by using the servo-controlled rock test system. The results show that the granite rocks undergoing a certain temperature (300℃) resist the lowest level of confining pressure and are the most prone to damage. Based on the ratios of strain increment to confining pressure decrement, it is quantitatively revealed that the unloading damage is caused by the intense radial deformation and volume expansion. The ratios of strain increment to confining pressure decrement all increase firstly and then decrease with the increase of temperature and reach the maximum value at 300℃. The deformation modulus gradually decreases during unloading by 33.20%~59.11% between 25℃~900℃, and the higher the temperature is, the more it decreases. The decreasing tendency is a quadratic polynomial relation with the volume strain. The Poisson's ratio increases gradually during unloading by 164.96%~274.03% between 25℃~900℃, and the higher the temperature is, the more it increases. The increasing tendency is linearly related to the volume strain. The post-high-temperature granite samples fail in the pattern of axial splitting under uniaxial compression with multiple transfixion cracks. And the rocks damage with cutting-through shear failure under triaxial compression. It is most complicated under triaxial unloading. The local shear failure with a large angle at the normal temperature turns into cutting-through with the increase of temperature, and returns to local shear failure again when the temperature reaches 900℃.