中文摘要：

以典型软岩-泥质粉砂岩为研究对象,进行了不同应力水平下的恒轴压、分级卸围压室内流变试验。试验结果表明,软岩在卸荷条件下的轴向及侧向流变变形较大,各向异性显著。在恒定围压较高时,轴向流变变形较大,而随着围压逐级降低,侧向流变变形发展较轴向更快,试样在破裂围压下的侧向变形远大于轴向。通过深入分析软岩卸荷流变试验成果可知,线性Burgers流变模型能较好地反映各级围压下流变曲线的衰减流变及稳态流变阶段,但对于破裂围压下的非线性加速流变阶段无法描述。基于上述分析,建立一个非线性损伤流变模型,采用Levenberg-Marquardt非线性优化最小二乘法对试验结果进行拟合,并获得软岩的非线性流变参数。经比较,拟合计算与试验曲线吻合程度很高,说明该流变模型能较好地反映软岩卸荷流变各阶段的曲线特征。

英文摘要：

Taking typical soft rock-muddy siltstone as research objective,the unloading triaxial rheological tests by constant axial stress and unloading lateral stress by steps are performed under different stress levels.According to experimental results,the axial and lateral rheological deformations are very significant and have strong aeolotropy.The axial rheological deformation is larger at higher confining pressures;while the development of lateral deformation is more rapid than that of the axial direction with the decrease of confining pressure.At failure confining pressure,the lateral deformation of sample is much more larger than that of the axial direction.After detailed research and analysis of the unloading rheological test results,the linear rheological Burgers model can preferably present attenuation and steady rheological stages of rheology curves at different confining pressures;but it can not describe nonlinear accelerative rheological stage at failure confining pressure.Based on the above analyses,a nonlinear damage rheological model is proposed.By taking the least square embedded in Levenberg-Marquardt algorithm,the test data curves are fitted to obtain the nonlinear rheological parameters of soft rock.By comparing with the test data,the fitting curves are well fitted with test curves.It is shown that the rheological model can preferably present unloading rheological curve characteristics of soft rock at various stages.