| Summary: | 博士 === 國立臺灣海洋大學 === 河海工程學系 === 94 === The purpose of this thesis is to study the behaviors of wave-induced seabed scouring and dynamic stresses in seabed in front of a vertical breakwater through a series of hydraulic model tests in a wave flume and a series of dynamical triaxial soil tests. A pressure measurement system and a non-contact seabed surface measurement system for movable seabed hydraulic model test, and a three cyclic triaxial testing system for soil tests were designed and setup for the studies.
In hydraulic model tests, the seabed scouring and dynamic stresses behavior in seabed were investigated and compared with current theories. The results show that all current theories overestimate the vertical and horizontal stresses and pore water pressure in seabed induced by waves, but underestimate the effective dynamic stress near the seabed surface. However, with the proper soil parameters, The theory proposed by Hsu and Jeng(1994) is more suitable than others.
The dynamic stresses behavior in seabed soil beneath the breakwater foundation is very complicated due to the combine actions of waves and the caisson motions. The seabed soil around the seaside toe of the caisson are found will release the soil pressure as dynamical pore water pressure increased and thus caused the highly potential to failure.
In dynamical triaxial soil tests, the dynamic soil strength in high porosity seabed can be replaced by fully drained soil shear strength in ordinary wave actions. However, in large storm wave actions, the dynamic soil strength should be replaced by the un-drained soil shear strength. The most possible place of shear failure can be occurred at the seabed near the toe of the breakwater.
Concluding as a whole, the interactions between wave, vertical structure and foundation soil are highly complicated, and should be investigated together. This study provides an experimental methodology to compensate the assumptions and simplifications in theoretical analysis, and information for the future related theoretical derivations and verifications, and also for the application in practice.
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