Fractal Approach On Pore Structure Of Rock And Soil Porous Media And Its Applications

As special engineering materials, rock and soil porous media show complicated and diverse engineering properties, which are controlled by their microstructures (or mesostructures), so it is very important to make deep research on their microstructures. The grains and pores in rock and soil porous media vary in shape and size, displaying disordered properties. However, in many other studies it has been shown that they are fractals. Consequently, the fractal theory has become accepted as a valid means to study the microstructures of rock and soil porous media. By using the fractal theory, the study on pore structure of rock and soil porous media was carried out and some valuable conclusions were gained.At first, two categories of fractal models of rock and soil porous media were established in this study. It was found that previous models can be unified by the two categories of fractal models, so the unified fractal models were formed.Afterward, the fractal dimensions of rock and soil porous media were classified and defined. A new method was presented to estimate the fractal dimensions in 3D space from the 2D structures of rocks and soils, thus the technique of digital image in 2D can be easily applied to obtain the fractal dimensions in 3D space. This study shows that the grain area (volume) fractal dimension and the pore area (volume) fractal dimension can exist simultaneously on a finite scale. The expression for the relationship between the two fractal dimensions was established. The experimental results of the microstructure of clay indicate that the expression is valid for estimating the pore area fractal dimension. The expression for the relationship between the fractal dimension of grain mass vs particle-size and the clay contents was founded, and its rationality has been verified by many experimental results.By using soil micromorphology technique, the mercury intrusion technique, the scanning electron microscope (SEM) and image analysis technique, the pore-size distributions of ecotypic revetment material (eco-material) and soft clay were gained. Moreover, the effects of soil depth and wet-dry cycling on the pore property of eco-material and the effects of consolidation pressure on the pore property of soft clay were investigated.Experimental results of pore distributions of soft clay and eco-material show the fractal models presented by this study are rational. The relationship between the calculation methods of fractal dimensions and the fractal behaviors of materials was studied. The results show the calculation methods of fractal dimension presented by this study are more effective and rational than previous means.At last, three new porosity models were developed to describe the pore-size distributions of porous media. Pore-size distributions of soft clay and eco-material in two- and three-dimensional spaces were used to study the applicability of proposed porosity models. The results show that the new porosity models are valid in describing the pore-size distributions of rock and soil samples.Based on the new porosity models, a new microstructure soil consolidation model was developed and the error of the compression strain prediction was less than 0.007 under low pressure. Several models for soil water retention curve were founded, which in form comprise previous models developed by other researchers, and they may be more accurate than previous models because of the valid mean for determining the fractal dimension. In addition, we obtained an expression for the relationship between soil cohesion and the test specimen size, as well as between the bulk density of rocks and soils and the test specimen size.