The Research About Seismic Subsidence Of Loess Controlled By Microstructure

China is one of the countries which are the most widely distributed of loess in the world. In the Northern China and North West loess areas, geological environment is very fragile, and geological disasters occur frequently. Seismic subsidence of loess has always been widespreadly concerned by the general engineering geologists. Constitutive relation based on the structural characteristics of soil is the core issue of loess mechanics.Loess is a typical structural soil. Seismic subsidence of loess is mainly controlled by its microstructure. Based on the structure of loess, through many seismic subsidence tests and high-power scanning electron microscope tests, the inherent damage mechanism of seismic subsidence of loess considered about microstructural elements is researched further by statistics microscopic damage mechanics. And a structure damage model of seismic subsidence of loess and constitutive relation is obtained. We count the microstructural parameters, research the orderliness of microstructural parameters variety corresponding to different sine wave dynamic stress number and found the relation between the microstructural parameters and the dynamic stress with soil microstructual quantitative analysis system. This paper discusses the regional seismic subsidence of loess and evaluation methods, and put forward an improved method of seismic subsidence of loess, in order to provide a scientific basis for engineering practice.This study covers the main aspects as following:(1) An overview of the characteristics of seismic subsidence of loess. It illustrates that seismic subsidence of loess is determined by its unique microstructure and external dynamic load commonly.(2) Microstructure experiments of loess are mainly completed by high-powered electron microscope. Process steps and precautions of obtaining microstructural images by high-powered electron microscope are introduced simply in this paper, in order to provide high quality pictures for quantifying the microstructural parameters. (3) We quantify the microstructural parameters by effecting the original microstructural images two image value with some image processing softwares such as Photoshop、Image-Pro Plus6.0and so on, using mathematical analysis softwares as Matlab and Excel to analyse and process datas, applying fractal theory. This study analyses the variation of microstructural parameters along with dynamic stress in the process of seismic subsidence of loess and establish a relatively reasonable quantitative relationship.(4) By the compare of microstructure changes between original loess and the loess after seismic subsidence, we obtain the result that seismic subsidence of loess results from the damage of particular trellis pores and granules of loess falling into trellis pores. In this paper, statistics microscopic damage mechanics is used to obtain a structure damage model of seismic subsidence of loess and constitutive relation. The damage of particular trellis pores of loess is described as a extension model and granules of loess falling into trellis pores is described as nucleation model. The phenomenological and structural mechanics theory is applied widely in this paper. Microstructural damage and macro destroying are linked to reveal the microstructural control mechanism of seismic subsidence of loess.(5) Through the multiple stepwise regression analysis between the microstructural parameters and seismic subsidence coefficient of loess, we bring forward a methodology and indicator determined microstructural theory estimating the seismic subsidence of loess to improve the seismic subsidence of loess, used in engineering practice, provide a new scientific theory for seismic subsidence protection and venue construction in Chinese vast loess region.