Geotechnical Engineering laboratory: NGUYEN VAN THINH
Effects of soil pressure in vibration and propagation directions of wave on shear wave velocity in the ground

Supervisor: Hirofumi Toyota

Infrastructures constructed on the soft ground have been frequently damaged by large earthquakes. The ground conditions should be considered in the ground vibration problem because their effects on dynamic stability of earth structures are very important. Shear wave velocity is an important factor to solve ground seismic problems related to design and analysis. Existing studies have treated the vibrations under relatively deep ground. However, little studies about dynamic properties of soils under the shallow ground, which is important for model tests, have been conducted. In this study, the shear wave velocity was measured using bender elements (BEs) in the model ground, which exhibits very low confining pressure. Used container’s dimensions are 100 cm length, 50 cm width, and 50 cm height. The model ground was created with Onahama sand at relative density Dr of 60%. The distance between transmitter and receiver of BEs was 5 cm. The stresses of wave’s vibration and propagation directions affect shear wave velocity. Therefore, wave’s vibration direction was changed from vertical to horizontal by the change of BE elements direction from horizontal to vertical. The earth pressers in vertical and horizontal directions were measured simultaneously. A plate hitting test was also conducted to confirm the consistency of this method.
From the experimental results, the following conclusions are obtained:
1.	Under a low confining pressure condition, the shear wave velocity linearly increases with the earth pressure to the power of 0.25.
2.	In horizontal propagation, the shear wave velocity with vertical vibration is greater than that with horizontal vibration. The reason is that the vertical earth pressure is greater than the horizontal one.
3.	The shear wave velocity can be uniquely determined by using the geometric mean of the vertical and horizontal earth pressure.
4.	The same shear wave velocity was observed in the plate hitting test instead of the BE test.