泥质粉砂岩蠕变特性及非线性蠕变模型研究

Study on Creep Characteristics and Nonlinear Creep Model of Argillaceous Siltstone

为揭示地下岩体非线性蠕变力学特性,对中风化泥质粉砂岩开展分级单轴加载蠕变试验。泥质粉砂岩典型蠕变曲线可划分为减速蠕变、稳态蠕变和加速蠕变阶段,使用给定蠕变速率阈值法求得的岩石长期强度为14.3 MPa。为了描述岩石非线性蠕变特性,引入了一个与时间应力水平相关的非线性黏塑性元件,将其与广义Kelvin体和带开关的黏性体串联,得到了改进的非线性黏弹塑性蠕变模型。使用Origin平台的Levenberg-Marquardt非线性最小二乘法反演得到模型的蠕变力学参数,通过将广义Kelvin蠕变模型、伯格斯蠕变模型和改进黏弹塑性蠕变模型与试验曲线进行比较,分析了各自的适用特点。结果表明:本研究提出的改进黏弹塑性蠕变模型可以较好地描述中风化泥质粉砂岩加速蠕变阶段特征,揭示了泥质粉砂岩的非线性蠕变力学特性。

The stability and rock long-term strength of underground rock mass engineering are closely related to the rock creep characteristics. With the deepening of resource exploitation,there are many mining rock mass large deformation and strong rheology problems. Therefore,the research of rock creep,especially the creep model under high stress condition,has great engineering significance and research value. Creep tests on moderately weathered argillous siltstone under graded uniaxial loading was carried out.The rock samples were machined into cylinders with dimensions of φ50 mm×100 mm.The stress loading level was 6~20 MPa,the stress increment was determined to be 2 MPa for each stage,and the stress remained constant for 72 h for each stage.The research shows that most of the creep deformation of moderately weathered argillaceous siltstone occurs at the moment of loading.When the creep stress is less than 12 MPa,the rock creep shows decelerating creep phase and even creep phase. When the creep stress is greater than 14 MPa,the rock creep shows decelerating creep phase,even creep phase and accelerating creep phase.The rock long-term strength obtained by using the given creep rate threshold method is 14.3 MPa. In order to describe the nonlinear creep characteristics of rock,a nonlinear viscoplastic element related to time and stress level was introduced. By connecting the nonlinear viscoplastic with a generalized Kelvin component and a viscous component with a switch,an improved nonlinear viscoelastic-plastic creep model was obtained,and the constitutive equation and creep equation of the improved viscoelastic-plastic creep model were given.The Levenberg-Marquardt nonlinear least square method of Origin platform was used to invert the creep model mechanical parameters. By comparing the generalized Kelvin creep model,Burgers creep model,improved viscoelastic-plastic creep model with the test results,obtain the applicable characteristic of each model. The generalized Kelvin creep model is suitable for describing the rock instantaneous deformation and decelerating creep phase at low stress level,and the Burgers creep model can describe the rock instantaneous deformation,decelerating creep and even creep phase very well. It is concluded that the improved viscoelastic-plastic creep model is suitable for middle-weathered argillaceous siltstone,which explains the nonlinear creep mechanical properties of mudstone formation well. The research results provide important guidance for further revealing the rock rheological properties and building rock creep model.