A 3-hinge arch precast structure which consists of an arch element produced in factory was developed as an arch structure instead of short-span bridge or cast-in-place culvert. Recently, this method was adopted in Japan, but in a seismically active area like Japan, it is necessary to study the a seismic characteristics of this structure.
In this research, shaking table tests were carried out to examine the effects of the density of foundation and the effects of intensity of shaking on the dynamic stresses induced in the 3-hinge arch and on the displacement of Terre Armee wall. In addition, a comparison between the experimental results and the analytical results obtained using existing two-dimensional seismic response analysis was performed.
Earth structures with precasted arch culvert and Terre Armee wall have been constructed in many parts of Japan. However, in a seismically active area like Japan, there is a need to study the seismic and shaking characteristics of the said structure. In this research, shaking table tests under two directional shaking in a horizontal plane were conducted to examine the effects of the shaking conditions, i.e., between one direction and two directions, on the dynamic stresses that develop in a 3-hinge arch and on the displacement of Terre Armee wall. Furthermore, the effect of friction between the ground and arch or strips was examined. Based on the results, the factors which are necessary to evaluate the seismic stability of the said structure are confirmed.
Several studies have concluded that the effect of matric suction on the shear strength of unsaturated soil is very important. However, little notice is given on the stress history due to unsaturation and drainage condition in the arrangement of these experimental results. This paper attempts to show the relationship between shear properties and matric suction under specified stress history and drainage condition.
In this study, an unsaturated specimen is set up by dehydrating the normally consolidated soil with controlled matric suction to a specified stress history. Triaxial apparatus and hollow cylindrical torsional shear apparatus are employed to examine the effects of stress history and drainage condition, respectively.
Through the systematic experiments, the effects of stress history and drainage condition on the stress-strain relationship are clarified. The increase in shear strength by matric suction which is measured at the point of maximum shear stress is observed to be independent of stress history and drainage condition. However, in strain softening behavior it was found that the ultimate strength is independent of matric suction and traces a unique line which is parallel to the critical state line on the pnet - q plane.
There are many cases in which ground is subjected to stress history not only via artificial actions but also by tectonic movement. The effects of stress history under three dimensional stress conditions are one of the important phenomena which have to be evaluated for the accurate prediction of ground deformation. The purpose of this study is to supply the fundamental data relating to stress history which can be incorporated in prediction or design techniques. To achieve this objective, a series of hollow-cylindrical torsional shear tests was conducted on saturated cohesive specimens which were subjected to shear history under constant p', various directions and three dimensional stress conditions.
From the experimental results, it was seen that the magnitude of the ultimate strength was the same for a given p' and not related to the shear history. On the other hand, the deformation characteristics(the elastic locus) behaved differently with respect to the shear history. The elastic locus developed by the stress history has directional and stress condition effects.
Finally, taking into account the experimental results of the present study, the predominant parameters -the difference in the direction of shear, and the stress condition between the shear history and the shear- were selected. Using these parameters, the elastic boundary space due to the stress history was confirmed to evaluate the effects of the shear history under three dimensional stress conditions.
Induced anisotropy under three-dimensional stress conditions is one of the important factors in the accurate prediction of ground deformation and should be kept in mind not only in the laboratory but also in the field. To achieve this objective, torsional shear tests for saturated cohesive soils with induced anisotropy were performed. Induced anisotropy was generated by the shear history under constant p' (effective mean principal stress), a (direction of major principal stress) and b (intermediate principal stress coefficient) conditions in this study. The parameters a and b were also set up during the shear history process, and the drained torsional shear tests were carried out under constant p', a and b conditions using these specimens. The behaviour of soils during this process was examined in detail.
The elastic boundary induced by the shear history was represented in three dimensional space. Furthermore, the uniqueness of this elastic boundary was examined by changing the stress level and the material of the specimen. In conclusion, the uniqueness of the elastic boundary induced by the pure shear history (consant p' ) on saturated cohesive soils was verified via these experimental results. The potential benefit in a wide range of soil mechanics was thus shown.
The failure criterion represented by matric suction is proposed on unsaturated soils. Although there is plenty of unsaturated ground under low confining pressure(lower than 100kPa) near the surface of the earth, the application of the failure criterion under low confining pressure has not been confirmed.
To achieve this objective, strength and deformation characteristics of an unsaturated cohesive soil were studied, with close attention paid to tensile stress using a hollow cylinder torsional shear apparatus. Experimentation was carried out under the conditions of constant suction, where it is easy to estimate the effect of matric suction. The difference between the failure mechanism under compressive stress and under tensile stress is investigated in this study. Then, the application range of the existing failure criterion is discussed with a focus on low confining stress range. Finally, new failure criterion on unsaturated soil considering tensile stress is proposed on the basis of the experimental results.