岩体结构面法向循环加载本构关系研究

对岩体结构面在法向循环加载下的受力变形关系进行了理论研究。试验表明,加卸载应力–变形曲线均可表示为双曲线函数,并且呈现不断硬化的特性,伴随产生法向残余位移。对已有双曲线型式的本构关系加以拓展,引入新的模型参数,假定卸载和重加载曲线均以结构面最大压缩位移为渐近线,曲线在法向力时为0的起始刚度由前一次循环过程的加载和卸载曲线起始刚度决定,从而完全确定循环加载本构方程。新参数体现结构面法向循环加载曲线的收敛速度和所产生的残余位移等受力变形特性,取决于岩石类型、结构面几何特征和填充物特性。通过设定参数的不同取值,这一模型分别等价于已有的不同模型。与无充填岩石裂隙和有厚度岩石夹层在法向循环加载下的试验结果对比表明,模型能较好描述岩体结构面的本构关系。

STUDY OF CONSTITUTIVE MODEL FOR ROCK INTERFACES AND JOINTS UNDER NORMAL CYCLIC LOADING

The constitutive models for rock interfaces and joints under cyclic normal loading are reviewed. From many tests it is concluded that the joint loading,unloading and reloading follow hyperbolic responses,and result in irrecoverable closure deformation with hardening of the joints. Based on the hyperbolic constitutive models,it is supposed that the unloading and reloading curves have the same asymptote which represents the maximal closure of the joint. For every loading step curve,the initial normal stiffness,which is defined as the normal stiffness at the zero normal stress point on the curve,is calculated from the initial normal stiffness of the previous loading and unloading curves. New parameters are introduced to represent the convergence velocity of constitutive curves and the irrecoverable closures,with their values depending on the rock types,the geometric characters and on the infill mineralogy of the rock interfaces and joints. With different values of the parameters,this model can be made equivalent to other models reviewed. Comparison with normal cyclic loading tests on natural clean joints and filled joints shows that this model could describe the constitutive relations of rock interfaces and joints with higher accuracy.