岩石裂隙法向循环加载本构关系试验研究

EXPERIMENTAL STUDY OF CONSTITUTIVE RELATION FOR ROCK FRACTURE UNDER NORMAL CYCLIC LOADING

法向变形对岩石裂隙渗流及应力波传播都有重要影响。在分析岩石裂隙法向变形机制的基础上,结合试验曲线循环滞后及其形状特点,探讨岩石裂隙在法向循环加载下的本构关系。试验得到粗晶及细晶大理岩裂隙岩样的15个循环加、卸载法向应力–闭合曲线。第一循环加载曲线与其他加、卸载曲线明显不同,其拟合曲线单独产生。平移其余加、卸载曲线使其低应力端点通过原点后,采用四参数双曲线–幂函数方程拟合所有曲线。加载累计闭合量和卸载残余闭合量与循环次数存在较好的指数函数关系,可确定循环加、卸载拟合曲线的2个端点;通过初次拟合得到加、卸载曲线幂函数项指数与循环次数的关系,再假定各加、卸载拟合曲线通过循环加、卸载拟合曲线的2个端点,获得幂函数系数的表达式;最后通过2次拟合,先后确定加、卸载曲线最大隙宽及初始刚度与循环次数的关系式。将各循环加、卸载曲线的3个参数拟合值代入双曲线–幂函数表达式,并平移各拟合曲线使其通过加卸载拟合曲线的2个端点,可得到拟合精度较好的连续拟合曲线。研究结果对循环加载下岩石裂隙法向闭合的数值模拟具有一定的实用价值。

The normal deformation of rock fracture has important influence on its seepage and stress wave propagation feature. A constitutive model for rock fracture under normal cyclic loading is studied on basis of analyzing normal deformation mechanism of rock fracture, cyclic hysteresis and shape characteristics of test cuCves. 15 circles of normal closure-stress curves of coarse-grain and fine-grain marble sample fractures are got through laboratory tests. The first cyclic loading curve, whose fitting curve should be generated alone, is significantly different from other loading or unloading curves. A hyperbolic-power function with 4 parameters is chose to fit each loading and unloading curve after translating every curve to let its low-stress endpoint locate at original point. Both the accumulative total loading closure and residual unloading closure have good exponential function relations with cyclic numbers, which can be used to determine two endpoints of each fitting curve. The expression of relationship between the power function index and cyclic numbers is got by first fitting~ and then, the expression of the power function coefficient is obtained by assumption of every fitting curve going through two endpoints of its corresponding fitting curve. Finally, the relationships of maximum aperture, initial stiffness and cyclic numbers are identified by next 2 times ot orclerLy nmng. raence me tsummuuu~ ~ e, ~, curves, which has higher fitting precision, can be determined by substituting the fitting values of three parameters into hyperbolic-power function expression; and then translating each curve to let its endpoints locate at the corresponding fitting points. The research has some practical values for numerical simulation of normal stress-closure curve of rock fractures under cyclic loading.