盐岩蠕变特性及其非线性本构模型

为了研究盐岩的蠕变特性,利用RLW-2000岩石流变试验机对盐岩试件进行了三轴压缩分级加载蠕变试验。试验结果表明:在围压一定的情况下,随着轴向应力增大,盐岩瞬时应变、蠕变应变以及蠕变速率等均随之增大,同时进入稳态蠕变阶段所需要的时间逐渐延长;等时应力-应变曲线显示,盐岩蠕变具有非线性特征,且其非线性程度与蠕变时间和应力水平有关,蠕变时间越长、应力水平越高,非线性程度越高。基于非线性流变力学理论,提出了一种非线性黏滞体,其黏滞系数是所加应力水平和蠕变时间的函数,将非线性黏滞体替换常规Burgers模型中的线性黏滞体,建立了可描述盐岩非线性蠕变特性的MBurgers模型,并根据盐岩蠕变试验结果,采用曲线拟合法对MBurgers模型的参数进行了反演识别。拟合曲线和试验曲线对比显示,两者吻合良好,误差较小,说明该模型可以描述盐岩的蠕变特性。

Creep properties of salt rock and its nonlinear constitutive model

In order to study the creep property of salt rock，triaxial compression creep tests with step loading axial stress to salt rock specimens were carried out on the RLW-2000 rock rheology testing machine.The test results show that the instantaneous strain，creep strain and creep velocity of salt rock increase gradually with the increasing of axial stress，meanwhile，the duration of the primary creep stage gradually extend.And isochronous stress- strain curves of salt rock indicate that the creep process of salt rock has nonlinear characteristic，and the nonlinear degree is related to creep time and stress level.Based on nonlinear rheological theory，a new nonlinear viscosity component with a variable viscosity coefficient was proposed，and the viscosity coefficient of which was time and stress- dependent.Then，by using this proposed nonlinear component to replace the conventional viscous components in Burgers model，a nonlinear viscoelasticity creep model，which was named MBurgers model and can describe the nonlinear creep property of salt rock was established.According to triaxial compression creep test results of salt rock，the parameters of MBurgers model were inversed by using curve fitting method.And the theoretical curves accord well with the test curves，which indicates that the MBurgers model can describe the creep property of salt rock.