砂岩分级加卸载蠕变特性试验研究

为了研究砂岩的蠕变力学特性,采用RLW-2000型流变试验机进行三轴分级加卸载蠕变试验。通过黏弹塑性应变分离的方法,得到砂岩在不同偏应力水平下的瞬时弹性、瞬时塑性、黏弹性和黏塑性应变,并对黏弹塑性应变及弹性模量的变化规律进行探讨。试验结果表明:岩石蠕变为黏弹塑性变形过程,加载过程中表现有瞬时变形、衰减蠕变阶段和稳定蠕变阶段,卸载过程中表现出瞬时及滞后变形恢复现象;岩石初始蠕变速率与稳态蠕变速率比较可达2个数量级的差异,均随偏应力水平的提升而递增;岩石等时偏应力-应变关系表现出明显的非线性特征,曲线逐渐偏于应变轴,岩石蠕变变形同时具有线性和非线性特征。研究成果可为地下工程的长期稳定性研究提供一定参考。

Experimental Study on Creep Characteristics of Sandstone under Step Loading and Unloading

Triaxial loading and unloading creep tests were carried out on RLW-2000 rheological testing machine to study the creep mechanical properties of sandstone. The instantaneous elastic, instantaneous plastic, viscoelastic and viscoplastic strains of sandstone under different deviatoric stress levels were obtained via viscoelastic plastic strain separation, and the variation rules of viscoelastic plastic strain and elastic modulus were examined. The experimental results demonstrate that: 1) the creep of rock is a viscoelastic plastic deformation process consisting stages of instantaneous deformation, decaying creep and stable creep during loading, as well as instantaneous and lagged deformation recovery during unloading. (2) The difference between initial creep rate and steady creep rate of sandstone could reach two orders of magnitude, both growing with the climb of deviatoric stress level. (3) The isochronal deviatoric stress-strain relation of sandstone shows obvious nonlinear characteristics, and the curve gradually deviates from the strain axis. The creep deformation of rock has both linear and nonlinear characteristics. The research findings could offer reference for the study of long-term stability of underground engineering.