摘要
变形带力学性质的鉴定是地质力学研究中的先行基础步骤。近来出现一些新的概念和方法,可用以定量表征变形带的力学性质。天然变形带通常是一般剪切作用的产物,是纯剪切(共轴缩短或伸展)和简单剪切的组合。为了定量说明两者间的相对贡献,提出了运动学涡度(Wk)这一物理量,并简单地定义为cosυ。υ是主变形面内两特征方向间的夹角。纯剪切的υ=90°,Wk=0;简单剪切的υ=0°,Wk=1。一般剪切的υ介于0°和90°之间,Wk为0到1。运动学涡度符号的正负分别代表变形带的减薄和增厚。υ可通过极摩尔圆法求出。主压应力(σ1)方向与Wk的关系为Wk=sin2ξ。ξ是σ1与变形带法线间的夹角。因此,可用以确定变形带的Wk和力学性质。根据最大有效力矩准则,韧性变形带与主压应力(σ1)方向间的夹角为55°,可用以确定古应力轴的方向,并可能确定变形时差应力的大小。
The determination of mechanical properties of a deformation zone is the first step in the geomechanical study. Some new concepts and methods have been proposed and can be used for quantitative characterization of mechanical properties of deformation zones. Natural deformational zones are commonly the result of general shear, a combination of pure shear （coaxial contraction or extension） and simple shear. In order to describe quantitatively their relative contributions, the kinematic vorticity number （ Wk ） is introduced and simply defined as cos v, where v is the angle between two eigenvectors containing the shear directions in the principal deformation plane （XZ-plane or ac-plane）. For pure shear, v = 90° and Wk = 0, and for simple shear, v = 0° and Wk = 1. General shear is a combination of the above two, whose v ranges between 0° and 90° and Wk from 0 to 1. The kinematic vortieity numbers may be signed as positive or negative. The positive and negative signs represent thinning and thickening of deformation zones respectively. The angle v between the eigenveetors is available in several ways by means of polar-Mohr constructions. Wk can be given by the orientation of the maximum principal stress （ σ1 ） ： Wk = sin 2ξ, where ξ is the angle between α1 and the normal to the deformation zone. Therefore, the related Wk and the mechanical properties of the deformation zone can be determined. Based on the maximum effective moment criterion, Meff = 0.5 （α1 - α3 ） Lsin2 a sina, where the angle a between a ductile deformation zone and the maximum principal eompressional stress axis is 55°. The relationship can be used to infer the stress-orientation and, potentially, the value of the differential stress when the deformation zone formed.
出处
《地质力学学报》
CSCD
2005年第3期197-203,共7页
Journal of Geomechanics
基金
国家自然科学基金资助项目(No.40272084和No.40472101)。
关键词
运动学涡度
极摩尔圆
最大有效力矩准则
kinematic vorticity number
polar-Mohr construction
maximum effective moment criterion
