恒轴压卸围压条件下粉砂岩应力应变特征与能量演化

为了获得高陡山区地下工程顶部粉砂岩在开挖后的应力应变和能量演化特征，开展了不同围压下粉砂岩恒轴压卸围压三轴试验，分析其应力应变、应变能转化以及能量耗散特征。结果表明，恒轴压卸围压条件下，围压越高，试样围压卸载率越低，且试样破坏越快、变形越大。不同围压下能量转化特征曲线趋势基本一致，与应力应变曲线有较好的相关性。围压恒定轴压升高阶段，除围压产生的应变能密度基本恒定外，其他能量演化曲线具有呈指数升高的特征；主要表现为原生孔隙压密，能量转化率较低。轴压恒定围压卸载至试样破坏阶段，轴向应力与能量曲线两者突变点基本对应；产生较大程度宏观破裂，能量转化率较高。试样破坏后围压恒定和继续施加轴向应变阶段，低围压能量释放更强，试样破坏更为碎裂。能量耗散具有总体上先升高后降低再陡增的特征，围压越低，试样破坏时应变越小、能量耗散比越大，试样破坏更加碎裂；围压越高，对试样能量耗散抑制作用越强，有利于弹性应变聚集，更容易产生岩爆现象。

Study on Stress-strain Characteristics and Energy Evolution of Siltstone Under Confining Pressure Unloading and Constant Axial Compression

For obtain the stress-strain characteristics and energy evolution characteristics of siltstone high and steep slope at the top of underground engineering after excavation, triaxial tests under constant axial pressure and unloading confining pressure were carried out to analyze the stress-strain characteristics, strain energy transformation characteristics and energy dissipation characteristics of siltstone under different confining pressures. The results show that the higher the confining pressure is, the lower the unloading rate of confining pressure is, and the faster the sample is destroyed and the greater the deformation is. The trend of energy conversion characteristic curve under different confining pressures is basically consistent, and has a good correlation with the stress-strain curve. At the stage of constant confining pressure and axial pressure increase, except that the strain energy density generated by confining pressure is basically constant, other energy evolution curves have the characteristics of exponential increase; It is mainly characterized by primary pore compaction and low energy conversion rate. The abrupt points of the axial stress and the energy curve basically correspond when the constant confining pressure is unloaded to the failure stage of the specimen. A large degree of macroscopic fracture occurs, and the energy conversion rate is high. When the confining pressure is constant and the axial strain is applied continuously after the failure of the specimen, the energy release of the low confining pressure is stronger, and the specimen failure is more fragmented. The energy dissipation has the characteristics of first increasing, then decreasing, and then increasing steeply. The lower the confining pressure is, the smaller the strain is, the greater the energy dissipation ratio is, and the more fragmented the specimen is. The higher the confining pressure is, the stronger the restraining effect on the energy dissipation of the sample is, which is conducive to the accumulation of elastic strain and the occurrence of rock burst.