Saturated Loess' Dynamic Model And It's Application To The Dynamic Interaction Of Pile-Soil-Structure System Under Earthquake

The pile foundation has a long history and still be widely used nowadays, it exhibits good seismic performance. But in the large earthquakes lately, the destroies of pile foundations were found to be commonly in different degrees and styles. The dynamic interaction of pile-soil-structure system under earthquake is a popular study in Geotechnical Engineering currently, and it's also a very difficult job. In this paper, the author pay attention to the loess area of our country, and then, on the basis of the established structral dynamic model of saturated loess, the earthquake responses of saturated loess field and pile-saturated loess-structure system are analyzed by finite-infinite element coupling method. The main research and results are as follows.1. Two different kinds of over-consolidated ratio are defined. Under un-drained tri-axial shearing tests of saturated loess, the effects of some factors, such as consolidated pressure, over-consolidated ratio and anisotropic consolidated ratio, on the un-drained deformation modulus and un-drained strength of saturated loess are analyzed. The stress share ratio is introduced to study the structure of saturated loess, it's variational regulations are studied combine with experiments.2. Under un-drained dynamic tri-axial shearing tests of saturated loess, the effects of five factors, which includes consolidated pressure, over-consolidated ratio, anisotropic consolidated ratio, dynamic shearing stress ration and loading frequency, on the degradation of un-drained deformation modulus and un-drained strength of saturated loess are studied, the regulation of super-pore pressure's development are also analyzed.3. The basic stress-stain relations is established to saturated loess. The un-drainied strength of K₀ normal consolidated saturated loess is deduced, and some modified is did to it considering the bond stress of soil grains. The variation relationship is put forward which between the un-drained strength of over-consolidated state to the ones of normal consolidated state, and some modified is did to consider the effects of intermediate principal stress, the different between tension and compression. The quasi-over-consolidated ratio is introduced to consider the effect of super pore pressure, and the formulation is applied to consider the influence of shearing strain. The degenerated formulation of saturated loess' deformation modulus and un-drained strength are deduced at last. The models and the tests results of the super-pore pressure development are summarized, and then the super-pore pressure development model is gave which was fit for the loess used in this tests.4. The established steps of saturated loess' dynamic model are gave, and some parameters included are studied combine with tests datum. The structure exertion coefficient is introduced and a calculated model is gave. The degradation formulations of saturated loess' un-drained deformation modulus and un-drained strength are deduced which consider the soil's structure. The structural dynamic model of saturated soil is build up and implimented using Fortran language, relevant validation is did through ABAQUS finite element program at last.5. On the basis of the established saturated loess' structral dynamic model, the earthquake responses of the loess field, end bearing pile-loess-structure and friction pile-loess-structure systems are analyzed by finite-infinite element coupling method. The effects of some factors, which include the change of soil' thickness, super-pore pressure, soil' structure, the change of groundwater level, the thickness of hard soil on the surface, the slenderness ration of pile, the mechanical characteristic of interface between pile and soil, the import mode of earthquake, on the earthquake responses of the loess field, pile-loess-structure systems, and some useful suggestions are gave to engineering practice.