饱水粗砂岩力学特性及能量机制

摘要

The effects of saturation on post-peak mechanical properties and energy features are main focal points for sandstones. To obtain these important attributes, post-peak cyclic loading and unloading tests were conducted on sandstone rock samples under natural and saturated states using the RMT-150B rock mechanics testing system. After successful processing of these tests, comparisons of stress-strain, strength, deformation, damage, and degradation of mechanical properties, wave velocity, and energy features of sandstone were conducted between natural and saturated states. The results show that saturation has evident weakening effects on uniaxial cyclic loading and unloading strength and elastic modulus of post-peak fracture sandstone. With the increase of post-peak loading and unloading period, the increases in amplitude of peak axial, lateral, and volumetric strains are all enhanced at approximately constant speed under the natural state. The increase in amplitude of axial peak strain is also enhanced at approximately constant speed, while the amplitudes of lateral and volumetric peak strains increase significantly under the saturated state. Compared with the natural state, the increase in amplitude of saturated samples’ peak lateral and volumetric strains, and the post-peak cyclic loading and unloading period all conform to the linearly increasing relationship. Under natural and saturated states, the damage factor (the plastic shear strain) of each rock sample gradually increases with the increase of post-peak cyclic loading and unloading period, and the crack damage stress of each rock sample declines rapidly at first and tends to reach a constant value later with the increase in plastic shear strain. Under natural and saturated states, the wave velocities of rock samples all decrease in the process of post-peak cyclic loading and unloading with the increase in plastic shear strain. The wave velocities of rock samples and plastic shear strain conform to the exponential relationship with a constant. Saturation reduces the total absorption energy, dissipated energy, and elastic strain energy of rock samples.%本文研究了饱水对粗砂岩峰后力学特性及能量机制的影响.为了获得这些重要的属性,采用RMT-150B型岩石力学试验系统对自然与饱水状态的粗砂岩岩样进行峰后循环加、卸载试验.在对这些试验进行成功处理后,对比研究自然与饱水状态下粗砂岩的应力-应变、强度、变形、损伤及劣化力学特性和波速、能量特性.试验结果表明:饱水对峰后破裂粗砂岩单轴循环加、卸载强度和弹性模量具有明显的弱化作用;随着峰后循环加、卸载周期的增加,自然状态下,峰值轴向、侧向和体积应变增幅均近似为等速率增加,饱水状态下,轴向峰值应变增幅近似等速率增加,而侧向、体积应变增幅均显著增加;饱水后粗砂岩试样峰值侧向应变、体积应变相对自然状态下的增幅与峰后循环加、卸载周期之间均符合线性函数递增关系;在自然与饱水状态下,各岩样的损伤因子(塑性剪切应变)随着峰后循环加、卸载周期的增加而逐渐增加,各岩样裂隙损伤应力随其塑性剪切应变的增加先期快速衰减,之后裂隙损伤应力近似趋于某一恒定值;随着峰后循环加、卸载周期的增加,岩样承载结构累计损伤程度不断提高,相应地其力学参数不断劣化衰减;自然与饱水状态岩样在峰后循环加、卸载过程中的波速均随着塑性剪切应变的增加而减小,两者之间均符合带有常数项的指数函数关系.饱水降低了岩样的总吸收能量、耗散能及弹性应变能.