Analysis of electron microscope images of soil pore structure for the study of land subsidence in centrifuge model tests of high-rise building groups

The scanning electron microscopy (SEM) images of soil pore structures were quantitatively analyzed for the study of land subsidence in the centrifuge model tests of high-rise building groups in this paper. The changes of the macrostructure and microstructure characteristics of the soils before and after centrifuge model test were studied, including the void ratio, the equivalent diameter, the circularity, the shape factor, the distribution of the orientation angle and the morphological fractal dimension of pores. The results demonstrated that the real filling rate can be estimated by 115% of the filling rate calculated by the Otsu method or be estimated by the normalized threshold of the SEM images between [0.34, 0.36]. Variations of the calculated filling rate with the adopted threshold showed the Gaussian function relationship. After the consolidation, 28.0% and 29.6% of the total pore area of the silty clay of layer No. 4 and the clayey soil of layer No. 8 were reduced, respectively, which illustrated the great compressibility and showed good agreement with the large macroscopic subsidence. The pores with radii more than 1 μm occupied the vast majority of the total pore area. The fractal dimension of the pore shapes decreased after the consolidation. Considering the changes of the average eccentricity and the average shape factor, during the soil consolidation, the pores were not simply flattened but parts of the boundaries of pores were compressed to be closed, which made the shape of pores more regular.