In this paper, we examine the crack extension behavior in the brittle material under the compression mixed mode loadings based on the energy release rate criterion. Two initial parallel cracks were inserted in the center of a disc-type test-piece made of a cement paste. The compressive loads were obliquely applied to the parallel cracks. We study the influencesto the crack extension behavior by changing, the loading angle, the friction of the crack surface, the difference of length between two cracks, the distance of two parallel cracks. The energy release rate is computed for the extending crack tips at the onset of crack kinking by using the E-integral which is path independent even for a path containing a kinking crack tip.
