Experimental Studies On Undrained Cyclic Behavior Of Loose Sands Under Complex Stress Conditions Considering Static And Cyclic Coupling Effect

The initial stress conditions for soil elements beneath the foundation under the building are usually rather complex. Before subjected to complicated cyclic loading induced by ocean wave and earthquake shaking, the principal stresses of subsoil element under the different places of building are not equal generally on three directions. The initial direction angle of maximum principal stress axe changes. Under this condition, the dynamic behavior of soils and the constitutive relation are very complicated. It is necessary to develop the experimental apparatus that can simulate complex condition of initial consolidation and cyclic shear and use it to investigate the correlation problem. It is not only basic problems of dynamic soils and geotechmcal earthquake engineering, but also the problems that have to solve for important project.In order to simulate complex stress path influences combined by initial consolidation condition and shear loading, the soil static and dynamic universal triaxial and torsional shear apparatus is developed. The effect of direction of principal stress on dynamic characteristic of saturated Fujian standard sand under complex stress condition is studied, such as dynamic deformation behavior of small strain, the relation of stress and strain, dynamic strength and the variations of pore water pressure and remaining strain. The findings based on this fundamental study will be instructive for improving design of important structures and foundation subjected to complex loading.On the basic of investigating the many problems about the design of the apparatus, the function demands and skill parameters are proposed. The apparatus is designed and newly facilized in Dalian University of Technology under the cooperation of Seiken Inc., Japan. The debugging and running of the complex and big apparatus has been finished. This apparatus can reproduce isotropic consolidation, anisotropic consolidation with different initial conditions, K consolidation. It can be used for complex stress conditions and stress path including static and dynamic triaxial test, static and dynamic torsional test, the cintinuous rotation of principal stress axes and can be used to perform various soil experimental tests of sands or clays. It is fulfilled the precision requirement for small strain behavior and large strain behavior. The results of experiment indicated that it is possible for this apparatus to simulate the complex stress path including rotation of principal stress axes. The precision of experiment can be improved by using with the loading sensors and small displacement sensors installed in the triaxial cell. It can be made out that the apparatus can realize many other kinds cyclic shear tests of stress path by changing the amplitude of vibration, phase difference and frequency of two cyclic loading.The apparatus is used to perform experimental tests of sand subjected to simple triaxial shear, simple trosional shear and verticalandtorsional coupling cyclic shear with different stress path. 12 types of test are perfomed under isotropic consolidation and third-directional anisotorpic consolidation with different effective consolidation pressures, different initial direction angle of principal stress, different initial deviator stress ratio to study the dynamic modulus and damping ratio behavior of small strain of sand under complex stress condition. The experimental results for different combination of various relevant parameters are reportedand systematically analyzed. It is shown through comparative studies that the relations between stress and strain and the variations of damping ratio with strain under isotropic consolidation are not influence by the manner of cyclic loading, the relations of E/E or G/Go~X/r also. The parameters of and are consistent under different cyclic shear test, E and 獷 too. Under anisotropic consolidation, it has been shown that the initial orientation of principal stress axes has a considerable influence on relations between stress and strain, the variations of modulus and damping...