Study Of Testing Model On Stress Wave Propagation In Rock With Joint

The studies in this thesis are supported and oriented by (UTRE) program which is a joint R&D program between the Defense Science and Technology Agency (DSTA) and the Protective Technology Research Centre (PTRC), Nanyang Technological University.In many countries such as Singapore, the surface land is very scarce. While the county is rapidly developing both economically and socially, the limited land space may, obstruct further development in the future. So the use of underground structures has become increasingly important. In many cases, these structures are embedded in rock or under rock layers. And these structures are even required to operate safely under high strain rate conditions such as those caused by explosions or earthquake. The behavior and safety of underground structures vastly depends on the responses of the surrounding medium to such conditions. So for this purpose, it is very important to study the properties, including static and dynamic properties, of the geologic materials and other subjects about the utilization of underground space.Distinguished frorn ordinary engineering media, rock masses consist of two components: rock materials and fractures. Commonly in rock engineering, fractures is the term used as a collective term for all discontinuities or features, ranging in different sizes, in a rock mass such as joints, faults and so on. The rock fractures usually produce the discontinuous and inhomogeneous nature of the rock masses, and significantly affect the properties and engineering behaviors of the rock masses, including their mechanical, seismic, hydrologic and thermal properties and behaviors. So considering fracture effects is a primary requirement for solving problems associated with rock masses, and the development of research and methods for rock discontinuities and their effects on rock masses has been a distinctive feature of rock mechanics and rock engineering.In this thesis, according to the principles of one-dimensional elastic-wave propagation, the SHPB tests were carried out for simulations of wave attenuation across the discontinuous geological media with fractures. The aim is to investigate the effect of water contents, thickness of sand layer in fractures and the impact energy of stress wave, which are considered to be the significant factors of the model in the study.The Split Hopkinson Pressure Bar (SHPB) is a standard experimental technique nowadays for performing tests under dynamic loading. Its success is mainly due to the accuracy of its measurements. For a better test result, the material of two pressure bars are made of granite, and the striking hammer is a pendulum. Stress wave propagation in rock with joint will be studied with the modified SHPB setup.According to the test and study results, the magnitude of stress decrease with an increase in the thickness of sand layer, and the peak stress of the transmitted waves also decrease when water content increases, but increases with an increase in the impact energy.Comparing the stress-strain relationship between dynamic and static tests, the strain rate under the dynamic test is higher than the static test because of a larger loading rate. So there will be a larger strain in the dynamic test when the stress of sand layer is the same in the static test.