冻融循环后砂岩卸荷过程应变能转化特征研究

为了探究寒区隧道围岩在开挖卸荷状态下的力学性质,研究经历不同冻融循环次数的砂岩在三轴卸围压过程中的应变能转化特征。结果表明：（1）随冻融循环次数增加,卸荷屈服过程中峰值强度明显降低,塑性变形过程中出现明显平台阶段;（2）应变能转化过程可分为四个阶段,在峰前卸荷过程中,轴压吸收的应变能主要转化为弹性应变能储存,而冻融循环产生的损伤则加剧了以上过程;（3）峰后应力跌落过程中,存储的弹性应变能迅速释放,耗散能迅速增加,环向回弹变形做负功消耗的应变能迅速增大;（4）破坏表现出张剪破坏特征,随冻融循环次数的增加,张裂纹数量增加,颗粒破碎更为明显。本研究对进一步揭示冻结岩石卸荷损伤破坏规律有着重要的意义。

Strain energy conversion behaviors of sandstone after freeze-thaw cycles under triaxial confining pressure unloading

Stress-strain properties and strain-energy conversion behaviors of sandstone are studied by conducting freeze-thaw cycling tests and triaxial tests under unloading conditions to understand the mechanical properties of sandstone surrounding an underground tunnel in a cold region. Results show that with the increasing number of freeze-thaw cycles, peak strength in the unloading yield process is significantly reduced and the strain varies gradually. Time variations in strain energy can be divided into four stages. During the pre-peak unloading, most of the strain energy due to axial pressure is converted into elastic strain energy, and the damage caused by freeze-thaw cycling intensifies this conversion. After the peak, the stored elastic strain energy is rapidly released, and the energy dissipated by plastic deformation and damage is rapidly increased. The strain energy consumed by circumferential deformation also increases rapidly. The failure mode of the specimens shows obvious characteristics of tensile failure. With the increasing freeze-thaw cycles, the number of tensile cracks increases and particle breakage becomes more pronounced. The results reveal the fundamental behaviors of strain-energy conversion and improve our understanding of the damage and failure of frozen rock in unloading.