13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- conclude that the stress intensity factor of the inclusion tip is affected by the local stress field around the inclusion. In the whole model, the local disturbance of the inclusion is controlled by the far field stress and the inner boundary pressure. Therefore, when the load changes, I ' K may be greater than IC K . And the new fracture may produce along the defect. The experiment will be done to prove it. 3. Experimental verification 3.1 Experimental equipments The experiments were performed in an improved large true tri-axial rock mechanics experiment system. Cubic model blocks of 500mm on a side were positioned in the high-pressure cylinder for simulating in-situ stress conditions. The random defects were added in the samples, and the initial artificial fracture was simulated by a thin plastic sheet. The appearance of the high-pressure cylinder, which is one of the main equipments, is shown in figure 2. Figure 2 The appearance of the high-pressure cylinder 3.2 The experiment process and results In fact, the critical stress intensity factor of the line inclusion is greatly difficult to measure. However, we can make a perceptual knowledge for the fracture propagation mechanism after re-fracturing in defect reservoirs by changing the size of the ground stress directly. There are six samples designed for the experiments. The stresses of three samples is applied as shown in table 1, where xσ and initial artificial fracture are in the same direction. Before re-fracturing experiment, we measured the rock mechanics parameters of the sample through a group of small samples. Elastic modulus of sample matrix is 2.4GPa, Poisson ratio is 0.23.
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