砂岩直接拉伸蠕变特性及Burgers模型的改进与应用

Direct tension creep behaviors of sandstone and improvement and application of Burgers model

应用自行研制的岩石直接拉伸装置对红砂岩进行了单轴直接拉伸蠕变试验,试验结果表明,在低应力状态下砂岩的直接拉伸蠕变由衰减蠕变和稳态蠕变组成,高应力状态下砂岩直接拉伸出现历时较短的加速蠕变阶段。在对蠕变特性分析的基础上对Burgers蠕变模型进行了改进,引入了一个非线性黏塑性体,并基于BFGS算法对拉伸作用下蠕变试验结果进行直接拟合。结果表明,基于BFGS算法的改进Burgers蠕变模型理论曲线与试验曲线吻合效果较好,引入模型的非线性黏塑性体其黏性系数ηN的初始值较大(1019以上),该非线性黏塑性体在砂岩的加速蠕变阶段起到主导作用;改进Burgers模型不仅可以描述砂岩直接拉伸状态下的衰减蠕变和稳态蠕变阶段,而且可很好地描述砂岩加速蠕变过程。

The direct tension creep of red sandstone is tested by means of the rock direct tension device developed by the authors.The test results indicate that the sandstone in direct tension under the low stress condition is characterized by primary creep and steady-state creep while under high stress conditions by a rather short accelerated creep stage.Based on the creep behaviors of the sandstone,the Burgers model is improved by introducing a nonlinear viscoplastic body,and the direct tension creep test results are fitted by using the BFGS algorithm.The improved Burgers creep model agrees with the experimental curve.The introduction of the nonlinear viscoplastic body with the initial viscosity value ηN as large as over 1019（MPa.h） implies that the nonlinear viscoplastic body in the sandstone acceleration creep stage plays a leading role.The improved Burgers model can describe the primary creep and steady-state creep of sandstone under direct tension and better describe the process of the accelerated creep.It is concluded that it is important to evaluate the effects of tensile on the stability of geotechnical engineering.