Microscopic mechanism study on the compression deformation for saturated clay with unimodal or bimodal pore structure

Microscopic pore structure plays a crucial role in understanding the macroscopic mechanical behavior of soil. In this study, saturated soil samples with unimodal or bimodal pore structure were investigated to explore pore characteristics during compression. The evolution of pore structure and stress transfer mechanism during consolidation were analyzed using a set of microscopic quantitative parameters with the low-field nuclear magnetic resonance (LF-NMR) technique. The results showed that large pores and inter-aggregate pores were compressed and transform into smaller pores during compression. Analysis based on geometric mean diameter and partial void ratio reveals that in unimodal soils, small pores and inter-aggregate pores deform simultaneously. However, bimodal soil exhibits staged compression: macropores are compressed first, followed by a stress transfer that leads to the compression of small pores at later stages. By employing the compression contribution ratio and micro-compressibility coefficient, the pore structure effect on the deformation mechanism was elucidated. The unimodal structure exhibits continuous compression characteristics with increasing stress sensitivity, whereas the bimodal pore structure displays an evolutionary pattern where stress sensitivity first increases and then decreases, eventually leading to a dense state of the soil.