Study On Pore Structure Fractal Evolution And Its Damagequantitative Of Soft Soil

With the development of economic construction in our country, a large number of engineering project construction, underground engineering including deep foundation pit, the subway also produce accordingly. These underground engineering a nots allow to ignore to impact on the surrounding environment, especially the ground subsidence due to excavation unloading,too large the displacement of soil layer, even collapse events such as building, caused serious economic losses and huge casualties, extremely adverse impact on society. Therefore, the problems of the natural soil structural damage due to soil mass excavation unloading, the creep damage deformation of underground engineering surrounding soils etc,it has been the geotechnical engineering to be solved. The microstructure of soil is the basis of its material existence, internal pore characteristics and distribution of soil is the internal cause of soil microstructure change, is to determine the main factors of physical and mechanical properties of soil. Therefore, study of soil microstructure has important significance.In this paper, based on geotechnical engineering and state key laboratory project "soft soil unloading damage model and its application in the safety assessment of underground engineering", making the study of the unloading process of soft soil under different confining pressure level pore structure fractalevolution and quantitative damage, the main contents are as follows:(1) From the definition of fractal and its determination methods, the background of the concept of the fractal dimension, the concept of fractal dimension, the study method of the fractal, the application of fractal, fractal theory application in the geotechnical engineering and so on six aspects to introduce the basic concepts of fractal theory, And introduced rock and soil fractal porous media model fractal model proposed by the pore volume, particle volume fractal model and pore size and particle size distribution fractal model by Tao.(2) The use of soft soil unloading test and the porosity measurement of soft clay, obtaining the pore distribution data, according to fractal dimension method of the paper, In2d space successfully obtained corresponding particle undisturbed area distribution fractal dimension and pore size distribution fractal dimension, thereby successfully describe the fractal characteristic of pore distribution, also proves the rationality of the fractal model in chapter2, and the conclusion is: the soft clay has fractal characteristics and can be said with fractal model of rock and soil mass; With the increase of unloading level, rock and soil particle size distribution fractal dimension D is smaller and smaller, the porosity distribution fractal dimension D is smaller and smaller.(3) According to the pore model of porosity of the three kinds of characterization, pore size distribution of the soft soil based on under different unloading level data, verify the applicability of the three kinds of model, and the relationship between porosity and fractal dimension, think in the whole process of unloading, with the increase of porosity fractal dimension on the whole, shows the tendency of decrease.(4) Definition of damage variable,and the linear relationship between fractal dimension and the damage variable shows that fractal dimension can describe quantitatively the unloading damage evolution process of soft soil, it represents the damage degree of soft clay, the damage linearly increase with the decrease of the fractal dimension.