Three-dimensional Construction And Quantitative Research Of Pore Structure Of Black Soil Under Freeze-thaw Conditions

The northeast black soil region is one of the most important commodity grain production area in China,and soil pore structure is an important index that influences the physic-chemical and biological processes.But natural conditions such as repeated freeze-thaw cycles have a significant effect on the soil pore structure and affect soil water infiltration and soil erosion process.In this study,the soils in the typical black soil areas of Northeast China were selected as the research objects,and unfreeze-thaw cycles?T₀?and 1?T₁?,5?T₅?,10(T₁₀),15(T₁₅)and 20(T₂₀)freeze-thaw cycles were set.Based on the combination of nano-industrial CT scanning and image analysis technology,three-dimensional reconstruction and visualization of pore structure were carried out to qualitatively and quantitatively study the variation rules of pore size,shape and characteristics and pore network characteristics in soil pore structure under freeze-thaw conditions.The main conclusions of this paper were as follows:?1?Two-dimensional and three-dimensional visualization of black soil pore structure were carried out by 3DMA?Rock and Image J software respectively,and qualitative analysis showed that the freeze-thaw effect increased the number and size of soil pores and changed pore shape.With the increase of freeze-thaw cycles,more irregular pores and slender pores appeared in soil pore space,and regular small pores gradually increased,and the pore structure became more porous.?2?The porosity,pore size distribution and pore number were quantitatively analyzed by 3DMA?Rock software,and the pore shape was quantitatively analyzed by Image J software.Freeze-thaw effect on soil porosity,pore size,pore number and pore shape was significant.With the increase of the number of freeze-thaw cycles,the soil porosity and the number of pores increased significantly?P<0.05?,and the pore equivalent diameter increased.The capillary and non-capillary porosity in the soil and the porosity of every shape increased significantly with the increase of the number of freeze-thaw cycles,and the capillary porosity was significantly smaller than non-capillary porosity?P<0.05?.After 10 freeze-thaw cycles,the proportion elongated porosity was significantly higher than the regular and irregular porosity,while the proportion of the number of elongated pores was significantly smaller than the proportion of the number of regular and irregular pores?P<0.05?.There was no significant difference in the total specific surface areas of pores between different freeze-thaw treatments,but the specific surface areas of elongated pores were significantly smaller than the specific surface areas of regular and irregular pores.?3?The pore network was constructed by 3DMA?Rock software to quantitatively analyze the variation of the medial axis paths,nodes and pore throats of the pore network structure.Freeze-thaw effect had a significant effect on the size and number of medial axis paths,number of nodes,number of pore throats,the distribution of throat surface areas and effective throat to pore radius ratios in pore network.With the increase of the number of freeze-thaw cycles,the number of medial axis paths,nodes and the pore throats increased significantly?P<0.05?.The distributions of the number of medial axis path lengths,throat surface areas,throat equivalent diameters and effective throat to pore radius ratios under 20freeze-thaw cycles were higher than other freeze-thaw cycles.The distributions of the number of each parameter under 5 and 10,0 and 1 freeze-thaw cycles were close to each other respectively,while the distributions of the number of each parameter under 5 and 10freeze-thaw cycles were higher than that under 0 and 1 freeze-thaw cycles.