Permeability of silty clay and its prediction model based on NMR T₂ double cutoff value

To investigate the relationship between soil permeability, pore structure characteristics, and their evolution during compression deformation, this study conducts consolidation permeability tests on undisturbed and remolded samples of silty clay from the Peijia Ying Station of the Jinan Metro. Nuclear magnetic resonance (NMR) tests are performed on samples under different consolidation pressures. The results elucidate the reasons for the high permeability of the undisturbed silty clay based on the variations in hydraulic conductivity and pore structure. A permeability prediction model is proposed, utilizing dual cutoff values from the NMR T₂ spectrum. The findings indicate that the undisturbed silty clay exhibits significant structural integrity, with permeability levels much higher than those of remolded soil with the same void ratio. As consolidation pressure increases, hydraulic conductivity gradually decreases. The T₂ spectrum of both undisturbed and remolded silty clay displays a bimodal structure. Based on the NMR dual cutoff values, the pore structure can be classified into three categories: micropores, mesopores, and macropores. The compression of macropores is identified as the primary reason for the reduction in hydraulic conductivity with increasing consolidation pressure. The proposed model takes into account the differences in fluid states within pores of varying diameters, as well as the effects of capillary tortuosity on soil permeability, effectively enhancing the accuracy of hydraulic conductivity predictions.