Similar Model Test Study On Propagation And Coalescence Of 3D Groove Cracks Under Uniaxial Compression

In the study of rock mechanics, about the rock mass primary crack initiation、expansion、evolution and penetrating characteristics are having been the focus and difficulty in researches. For the study of 3D fractured rock problems, usually simplified by the 2D case, and much research results are obtained in the test and numerical simulation. But through the 2D simplified model can not fully describe the 3D information about fractured rock mass crack propagation and coalescence process. So this paper aims to study the mechanism of 3D cracks initiation、expansion、evolution 、penetrating and the damage fracture characteristics of 3D fractured rock mass through 3D cracks similar model test, the conclusions can be acted as some references for rock mass engineering design、construction and stability analysis.In order to observe the propagation、coalescence and penetrating phenomenon of 3D cracks more intuitively and clearly, selecting a organic glass material(PMMA) as the model material, which has an excellent transparency. In addition, PMMA has similar features to the rock brittleness at-50 Degrees Celsius low temperature. In order to describe the experimental phenomena better, this paper has a uniform definition of relevant characteristics about several new cracks under uniaxial compression conditions, include: wing crack(package type and split type), petal shaped crack, shell shaped crack. This paper designs a group、two group、four group crack layout, there are different angle in each crack, the main work of this paper are as follows:① In the experimental process mainly observed three types of cracks: wing crack(package type and split type), petal shaped crack,shell shaped crack.② The 3D crack initiation basically appear in the prefabricated crack tip, wing cracks are appeared firstly, when crack initiation angle is small, the direction perpendicular to the crack surface; when crack initiation angle is bigger, the crack initiation direction gradually close to the vertical direction.③ The crack extended form is mainly controlled by the size of prefabricated crack angle, A, B, C three groups of specimens are presented in this law, 30 degrees is wrapping layout expansion, 45 degrees, 60 degrees and 90 degrees are split type expansion.④ With the increase of the inclination angle, the peak strength of the specimens decreased gradually; under the arrangement of 45 degrees,is most likely to occur the phenomenon of crack initiation and propagation; when the angle is 0 degrees, the phenomenon is not obvious.⑤ With the change of angle and end to end distance, peak stress, crack initiation stress, crack initiation stress level are present certain regularity, this law is consistent with the law in 2D cracks similar tests.⑥ Using the SPH program simulate 3D cracks initiation, propagation, connection process of four root cracks under 45 degree, its propagation rules has a certain degree of agreement with the test phenomena,but in the test was not observed anti-wing cracks which appeared in the numerical simulation.