斜坡失稳过程的非线性演化机制与物理预报

Nonlinear evolutionary mechanisms and physical prediction of instability of planar-slip slope

对应变软化介质材料组成的平面滑动型斜坡,采用Weibull分布描述它的剪应力与应变关系。建立了斜坡系统的尖点突变模型,给出了失稳的充要力学判据,发现斜坡失稳与刚度比和材料的均匀性指标有极大关联性,水的一种重要新作用是增加材料的均匀性(脆性)和降低刚度比。考虑应变软化介质的粘性或蠕变性,建立了斜坡演化的非线性动力学模型——物理预报模型,并给出了根据滑坡位移观测数据反演非线性动力学模型的方法和稳定性判别准则。对鸡鸣寺滑坡根据观测序列进行了动力学模型的反演分析,一个重要发现是:|D|值在加速蠕变阶段陡增出现峰值,而后在接近失稳点时趋于零。根据斜坡在等速蠕变阶段的特点,提出了一个简化的非线性动力学模型和物理预报模型,研究了其分叉和混沌特征,给出了判别混沌的力学准则,发现混沌能否产生取决于滑面介质的力学参数。

A cusp catastrophe model of landslides was presented and the necessary and sufficient conditions leading to landslides were discussed. The sliding surface of the landslides was assumed to be planar and was a combination of two media： medium 1 was elasto-brittle or strain-hardening and medium 2 was strain-softening. The shear stress-strain constitutive model for the strain-softening medium was described by the Weibull＇s distribution law. It was found that the instability of the slope relied mainly on both the stiffness ratio and the homogeneity index of the media and that a new role of water was to enlarge the material homogeneity or brittleness and hence to reduce the stiffness ratio. A nonlinear dynamical model （or called a physical forecasting model）, which was derived by considering the time-dependent behavior of the strain-softening medium, was used to study the time prediction of landslides. An algorithm of inversion on the nonlinear dynamical model was suggested for seeking the precursory abnormality and abstracting mechanical parameters from a series of observed landslide. A case study of the Jimingsi landslide was conducted and its nonlinear dynamical model was established from the observation series using the algorithm of inversion. It was found that the catastrophic characteristic index ｜D｜ closed to zero prior to instability after it attained a high peak value and the slope evolved into the tertiary creep, and it could be regarded as an important precursory abnormality index. By taking into account the evolutionary characteristic of the slope in the secondary creep, a simplified nonlinear dynamical model was put forward for studying the properties of bifurcation and chaos. It was revealed that the emergence of chaos depended on the mechanical parameters of the sliding-surface media.