含弱面砂岩非线性黏弹塑性流变模型研究

 利用CSS–3940YJ型岩石剪切流变试验机，对向家坝水电站左岸坝基挤压带含弱面砂岩进行剪切流变试验。试验结果表明：该岩石属于典型的软岩，在恒定剪应力水平下具有显著的亚稳定蠕变特性。在应力达到一定水平时，岩石经过衰减和亚稳定蠕变之后发生加速蠕变破坏。根据含弱面砂岩剪切蠕变特性，对非线性流变元件进行改进，定义其在应力阈值前后分别等同于牛顿黏壶和非线性黏塑性体。将改进的元件与广义Kelvin模型串联，组合成四元件流变模型。该模型可以充分反映岩石亚稳定蠕变和加速蠕变特征，并具有结构简单、参数少的优点。推导四元件流变模型的本构方程，从理论上对岩石非线性蠕变特性进行分析。采用所建立的模型对岩石进行剪切流变力学参数辨识，并研究应力水平超过阈值后的参数辨识方法。通过模型计算结果与试验结果的比较，对提出的非线性黏弹塑性流变模型进行验证，显示所建模型的正确性与合理性。

STUDY OF NONLINEAR VISCOELASTO-PLASTIC RHEOLOGICAL MODEL OF SANDSTONE WITH WEAK PLANE

The sandstone with weak plane is sampled from the compressive zone of the left bank dam foundation of Xiangjiaba hydropower station. Shear rheology tests are carried out for the rock by using CSS–3940YJ rock shear rheology testing machine. The test results show that the sandstone is the typical soft rock，and the rock shows significant metastable rheological property under the constant shear stress. When the stress reaches a certain level，the accelerative creep damage of rock occurs after the primary creep and metastable creep. The nonlinear rheological component is improved according to the shear creep behavior of the sandstone with weak plane，and it is equivalent to Newton dashpot when the stress is less than threshold as well as nonlinear viscoplastic component when the stress exceeds threshold. By connecting the improved rheological component and generalized Kelvin model in series，a new four-component nonlinear viscoelasto-plastic rheological model of rock is proposed，which can fully reflect the metastable and accelerative creep properties of rock material. The model has advantages of simple structure and few parameters. The constitutive equation of this rheological model is deduced；and the nonlinear creep property of rock is carried out based on the theoretical analysis. The shear rheological parameter identification of the rock is carried out based on the proposed model，and the method of parameter identification is mainly investigated when the stress level exceeds the threshold. The comparisons between calculated results of nonlinear rheological model and tested results show that the proposed nonlinear viscoelasto-plastic rheological model is available and reasonable.