The study of plastic strain gradient and class Ⅱ behavior of rock

In this paper the theory of plastic strain gradient has been put forward and thereby the problem is discussed on whether the deformational behaviour of the rock of class Ⅱ is exist. It has been proved that the existence of the deformational behaviour for the rock of class Ⅱ is conditional, that is , when 1-2 π EλlL>0 the behaviour manifests itself. The influence of the height of rock specimen, the descending modulus λ of rock and the internal length l on the class Ⅱ behavior has been discussed.