加卸载应力路径对砂岩能量演化机制的影响

Influence of Loading and Unloading Stress Paths on Energy Evolution Mechanism of Sandstone

为了明确应力路径对砂岩能量演化的影响,采用RMT岩石力学试验系统开展了砂岩三轴和不同卸围压速率试验,详细分析了不同应力路径下砂岩破坏过程中吸收总能量、弹性应变能和耗散能的演化规律。结果表明,加载和卸围压应力路径下,砂岩屈服前吸收的总能量基本都以弹性应变能的形式存储,弹性应变能的增速与吸收总能量的增速保持一致,并逐渐增大。弹性应变能在单轴时经历较短的慢速增加阶段;三轴时随着围压的增大,慢速增加阶段越加显著,且在后期其增速很小;卸围压阶段弹性应变能基本保持不变。砂岩单轴耗散能出现较早表明内部损伤发展较早;三轴屈服阶段后期耗散能增速加快表明该阶段内部损伤发展加快;卸围压阶段耗散能线性增大表明内部损伤稳步发展。砂岩峰值处弹性应变能与吸收总能量的比值在单轴时最大,随着围压或初始围压的增大逐渐减小并趋于稳定;在相同围压下,卸围压应力路径下弹性应变能与总能量的比值小于三轴加载应力路径下的比值。在0.01 MPa/s卸围压速率下,弹性应变能与吸收总能量的比值受初始围压影响大,而1 MPa/s卸围压速率下,受初始围压影响小。砂岩弹性储能极限随着破坏时围压的增大按线性规律增大,加载应力路径相对卸围压应力路径能够提高砂岩的弹性储能极限。以上成果从能量演化角度分析了地下工程稳定性,具有一定的指导意义。

Triaxial compressive and different unloading confining pressure rates tests of the sandstone were carried out to investigate the influence of the stress paths on the energy evolution mechanism using RMT rock mechanical test system.The evolution rules of total energy absorbed,elastic strain energy and dissipation energy,in the process of sandstone failure under different stress paths,were analyzed in detail.The results show that under loading and unloading confining pressure stress paths,the total energy absorbed by sandstone before yielding is basically stored in the form of elastic strain energy,and the growth rate of elastic strain energy is consistent with that of total energy absorbed,and gradually increases.Under uniaxial loading,the elastic strain energy undergoes a short period of slow increase.The slow increase stage is significant during triaxial loading with the increase of confining pressure,and the growth rate is very small in the later stage.The elastic strain energy remains unchanged during unloading confining pressure stage.The early appearance of dissipation energy under uniaxial compression test indicates the early development of internal damage.In the later stage of yield under triaxial compression,the dissipation energy increases faster,which indicates that the internal damage development is accelerated.The linear increases of dissipation energy in the stage of unloading confining pressure indicates the steady development of internal damage.The ratio of the elastic strain energy at peak of sandstone to the total energy is the largest under uniaxial compression,and decreases gradually with the increase of confining pressure or initial confining pressure and tends to be stable.At the same confining pressure at failure,the ratio under unloading confining pressure is smaller than that under the stress path of triaxial loading pressure.The ratio of elastic strain energy to the total energy is greatly affected by the initial confining pressure at the rate of 0.01 MPa/s unloading confining pressure,while it is slightly affected by the initial confining pressure at the rate of 1 MPa/s confining pressure.The elastic strain energy limit of sandstone increases linearly with the increase of confining pressure,compared with unloading confining pressure stress path,loading stress path can improve the elastic strain energy limit of sandstone.The results provide guidance for the analysis of the stability of underground engineering from the perspective of energy evolution.