Investigation on strong vertical permeability and micro-pore characteristics of Jinan red clay using X-ray micro-tomography

Due to the peculiarity of the spring domain strata in Jinan, the phenomenon of serious water seepage appears in the process of excavation. The macro permeability of soil is closely correlated with its microstructure. In this study, using the X-ray micro-tomography (micro-CT) system and a self-designed soil seepage device, the internal pore structure of Jinan red clay and the water flow inside the sample under different seepage stages were observed. The microstructure of water phase and air phase in the sample was segmented by the watershed algorithm. Calculation and comparison of pore and throat size distributions and coordination number (CN) at different seepage stages were conducted by establishing pore network model (PNM). Meanwhile, the seepage experiment simulations were conducted based on the 3D pore structure of red clay. The results show that the preferentially flow of Jinan red clay is obvious due to the existence of the vertically developed macropore channel. The fine particles (mainly silt particles) are washed away during seepage, thereby expanding the pore channels. The maximum pore radius and pore connectivity have important influence on seepage characteristics of Jinan red clay, but the correlation between porosity is small.

Automated summary

Due to the peculiarities of the spring domain strata in Jinan, there is serious water seepage during excavation. The macro permeability of soil is closely related to its microstructure. This study used micro-CT and a self-designed soil seepage device to observe the internal pore structure and water flow of Jinan red clay under different seepage stages. A pore network model was established to calculate and compare pore and throat size distributions and coordination number. Seepage experiments were conducted based on the 3D pore structure of red clay. The results showed that the preferential flow of red clay in Jinan is obvious due to the presence of vertically developed macropore channels. Fine particles are washed away during seepage, leading to the expansion of pore channels. The maximum pore radius and pore connectivity have a significant influence on the seepage characteristics of Jinan red clay, but the correlation with porosity is small.