水-力耦合作用下砂岩松弛特性试验与本构模型

Experiment and Constitutive Model of Relaxation Behavior of Sandstone Under Water-Force Coupling Action

采用电液伺服三轴试验系统,对不同围压和水压条件下的红砂岩进行分级加载应力松弛试验.分析砂岩水-力耦合作用下全应力-应变过程的应力松弛量、应力松弛速率的变化规律.将含水开关与西原模型串联,实现应力松弛和水压在本构关系上的耦合,建立非线性砂岩松弛模型.结果表明:同一围压下,砂岩松弛量随着应变水平的提高而增加,砂岩松弛量在软化阶段达到最大;同一围压、同一应变水平下,砂岩松弛量随着水压的增加而降低,表现出水压对砂岩应力松弛具有抑制作用;改进的西原模型能较好描述砂岩应力松弛各阶段的力学行为,模型参数E_(1),E_(2),η_(1),η_(2),η_(3)在软化阶段之前随应变水平的提高呈现非线性增长;各阶段砂岩松弛速率呈“L”形,松弛速率快速下降为减速松弛阶段,松弛速率平稳下降为稳定松弛阶段.

The step loading stress relaxation experiment of red sandstone under different confining pressure and water pressure are carried out by electrohydraulic servo triaxial experiment system.The variation of stress relaxation amount and stress relaxation rate of sandstone in the whole stress-strain process under the water-force coupling action is analyzed.Connecting the water switch with Nishihara model in series,the coupling of stress relaxation and water pressure in constitutive relation is realized,and a nonlinear sandstone relaxation model is established.The results show that,under the same confining pressure,the amount of sandstone relaxation increases with the increase of strain level,and the relaxation amount reaches the maximum at the softening stage.Under the same confining pressure and strain level,the relaxation amount of sandstone decreases with the increase of water pressure,which shows that water pressure has a restraining effect on the stress relaxation of sandstone.The improved Nishihara model can well describe the mechanical behavior of sandstone stress relaxation in each stage.The parameters E_(1),E_(2),η_(1),η_(2),η_(3)of the model increase nonlinearly with the increase of strain level before the softening stage.The relaxation rate of each stage presents"L"shape,the rapid decrease of the relaxation rate is a slow relaxation stage,and the steady decrease of the relaxation rate is a sta-ble relaxation stage.