Abstract: In order to study the difference of the pore shape complexity among different loesses and the influence of stress path on the pore shape complexity, the pore fractal features are investigated on two kinds of loesses before and after stress path tests. Firstly, the reliabilities for calculating the fractal dimensions of pore by three fractal models are checked. Then the thermodynamic model is adopted to study the difference of pore fractal dimensions of two different kinds of loesses and the change of pore fractal dimensions after stress path according to the pore distributions of loess and filling loess around ground fissures, which are determined by mercury intrusion and withdrawal test. The change of pore shape is obtained based on the assumption that the pore is composed of sphere-shaped pore and tube-shaped pore. The results indicate that the pore fractal dimensions obtained by thermodynamic model are reasonable and reliability. The initial natural filling loess or initial remoulded filling loess has more complex pore structure compared with natural loess or remoulded loess. The void ratio decreases, the pore fractal dimensions increase and a part of sphere-shaped pores turn into tube-shaped pores after conventional triaxial compression tests. Compared with conventional triaxial compression test, the pore fractal dimensions of the sample and the ratio of the volume of tube-shaped pores to the total volume of pores after reduced confining pressure in triaxial compression test are smaller. In general, the tube-shaped pores possess larger fractal dimensions, the fractal dimensions are almost independent of stress path, compared with sphere-shaped pores, the ratio of the volume of tube-shaped pores to the total volume of pores increases with the decrease of void ratio.

Key words: loess, stress path, pore shape, fractal dimensions, thermodynamic model