Experimental Research On Dynamic Behavior Of Saturated Calcareous Sand Under Complex Stress Conditions

Calcareous sand is a special geotechnical medium which composes much carbonate and has obvious different mechanical properties from the general sand. It is generated in marine environment and widely distributed in South China Sea. In the ocean conditions and as the foundation of marine structures, calcareous sand is not only under complex initial consolidated stress state, but also subjects complicated dynamic load induced by wind, ocean wave and earthquake shaking, so its dynamic stability directly influenced the safety of the above building. Since the dynamic behavior of calcareous sand under complex stress condition is seldom researched, so it has very significant academic meanings and engineering value to study the calcareous sand's dynamic behavior under complex stress condition, which can develop and perfect the mechanical behavior investigation of calcareous soils, guide design, construction and assessing the stability of practical projects in marine condition, it can also exploit and defend the rich petroleum resource and reef island tourism in our South Sea.The dynamic behavior of calcareous sand under complex stress condition is studied systematically by performing a large number of tests such as vertical-and-torsional coupling cyclic shear test, simple trosional shear test, simple cyclic vertical shear test and simple triaxial shear test, using an advanced universal triaxial and torsional shear apparatus which can perfectly simulate the complex initial consolidated stress state and complicated dynamic stress. The main work and research findings are listed below.1,The dynamic strength experiment under high strain conditions is carried out to study the dynamic strain character of calcareous sand in complex stress state. Some factors influenced the development of dynamic strain are analysed such as initial deviator stress ratio, initial mean effective consolidated stress, initial direction angle of principal stress, parameter of intermediate principal stress and application way of cyclic load. The development model of dynamic strain has been put forward, that is Boltzmann curve or hyperbola.2,The development character of dynamic pore water pressure is investigated by analyzing the pore water pressure test curves and various effected factors. Then the development model of dynamic peak pore water pressure has been suggested. The determination method of peak pore water pressure with the accumulative generalized strain is proposed based on the relationship of peak pore water pressure and the accumulative generalized strain.3,The liquefaction nature of calcareous sand is studied and the liquefaction mechanics in complex stress condition is obtained. Mechanics of liquefaction under isotropic consolidation is different from under anisotropic. The liquefaction mechanics under isotropic consolidation is cyclic mobility or flow slide, while under anisotropic it isn't liquefyied in all test condition.4,Based on the analysis of dynamic strain, pore water pressure and liquefaction nature, the dynamic strength character is researched and the strength equation is suggested. Then the dynamic strength under various cyclic load is compared.5,The character of dynamic stress-dynamic strain combat combined with dynamic modulus and damping ratio are studied by dynamic tests of low strain. The skeletal curves model of dynamic stress-dynamic strain is achieved and all the factors affected it are analysed. Then features of dynamic elastic modulus and dynamic shear modulus are researched and the calculational methods of then are proposed. At last, the axial damping ratio and torsional damping ratio are studied.