| Fractured rock mass is usually met in most of the rock mass engineering and environmental engineering. Under different kinds of loads, the crack initiation, propagation, coalescence and interaction may induce the degradation of mechanical properties, even damage of the rock mass material. Therefore, the growth and evolvement features, fracture pattern, and the influence on rock strength of flaws in the rock mass are always focused by the researchers of academic and engineering fields.Because of the difficulties of mathematical treatment and phenomena observation on 3-D problem, people usually simplify the 3-D crack problem to 2-D situation. But most cracks are under 3-D stress condition (internal crack or surface crack), such simplification would lead to error. So, the study of crack propagation mechanism and the influence on the material strength become important research subjects in Geotechnical Engineering.Up to now, there have been some experimental studies about crack propagation mechanism in rock mass under compressive stress. Because of the constraint of experimental equipment and technology, there are quite few studies on the crack propagation mechanism of rock mass under tensile stress. Compared to the compressive strength, the tensile strength of rock mass is very low. Under low tensile stress, the cracks in rock mass will initiate, grow and coalesce, resulting in the damage of rock mass. The tension stress zone is inevitable met in the geotechnical projects, so the study of crack propagation mechanism in rock mass under tensile stress and its influence on the rock strength is full of theoretical meaning and application value.Both experimental test and the numerical simulation are effective methods to study the crack propagation problems. In this paper, the two methods are combined to do the following research work:1. By reading lots of literatures, analyze and compare the advantages and disadvantages of the materials used in the similar researches. According to practical situation, develop a kind of mortar material with good brittleness, the physical and mechanical parameters of which are closed to the real rock material. So the mortar material is a good alternative of real rock material, with the advantage of making pre-exist flaws conveniently. 2. Improve the clamp method and bonding method used most frequently in the tensile test of brittle material. Design and make a sample die with the shape of end region enlargement, a clamp matching with the sample, and axial direction location device, which suit for the axial tensile experiment of brittle material.3. Make samples containing different kinds (different dip angle, different distance between two cracks, different amount of cracks) of internal cracks. Carry out axial tension experiments with those samples, and obtain the stress-strain curves of all the samples, at the same time observe and analyze the loading and deformation course of samples. Finally, conclude the 3-D internal crack growth rules and the influence on the material strength.4. Make samples containing single surface crack with different dip angle. Carry out axial tension experiments with those samples, and obtain the stress-strain curves, at the same time observe and analyze the loading and deformation course of samples. Finally, conclude the 3-D surface crack growth rules and the influence on the material strength.5. Using the FRANC3D numerical program, compute and analyze the distribution of stress intensity factor and energy release rate along the tips of different forms of internal and surface cracks under axial tensile stress, and simulate the 3-D crack propagation course.6. Combining the results both from the test and numerical simulation, obtain some valuable conclusions, and give some advice to the rock mass engineering.
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