有限单元法在地质力学中的应用

地质构造体和岩体是一种岩性和结构高度变化的非连续而且非均一的介质,在压力(包括岩体中的间隙水压力)和温度的作用下所产生的变形和破坏现象,不仅为非线性关系,并随空间和时间而变化。对某一点而言,这种关系会由于作用力的大小和时间的长短,由弹性过渡到塑性或粘性状态。对整体而言,在同一时间内,却会在不同的部位出现不同的应力状态和变形的程度。

ON THE APPLICATION OF FINITE ELEMENT METHOD IN GEOMECHANICS

The major problem in geomechanics is shortage of a suitable method to evaluate quantitatively the stress-strain-rupture-time relationships of rock masses or tectonic units under any loading and arbitrary boundary conditions. The difficult is due either to heterogeneities and discontinuities of a geological environment causing nonlinear behavior of deformation and nonuniformity of stress distribution, or to the changes of temperature and/or of interstitial water pressure sometimes highly modifying their stress conditions and thus affecting their deformation and strength characteristics.During deformation, a given type of rock mass or a particular set of geological structure can behave as brittle member in one part of the medium and at the same time as a ductile one in another. Evem in the same location they may behave as a brittle material early in the deformation, but later in a ductile manner. The folding process of earth ’s crust usualy with very low strain rate, subjecting to viscous or plastic flow behavior as a whole, may initiate brittle cracks in localized upper regions and develop ductile rupture in lower layers.All these phenomena operate as progressive deformation and failure mechanisms accompanied by stress dropping. Time scales range from those geologic to few seconds-involved in earthquakes, spatial variations from crystal to crystal up to regions several hundred kilometers thick and wide-concerned with deep-seated tectonic movements. The concept of the ideal physical continuum cannot thus be expected to apply directly without modification to taking into account these time and space dependent factors. Of modern numerical processes, finite element method does have the generality of allowing the complex reality to be dealt with, but effort in order to meet these requirements should be centered on to distinguish between the response of a small laboratory specimen under varying conditions of confining pressure, interstitial water pressure, temperature and even time, and the bulk behavior of its natural counterpart, so as to relate the experimental phenemena to the geological activities.This paper, being concerned in principle with the application of finite element method to geomechanieal problems, cannot deal with extreme details. If the general principles and possibilities offered by the method have been made clear, the objective of the paper has been achieved.