Consolidation and Permeability Characteristics of Soft Clay in the Lower Huaihe River Alluvial Plain

This study investigates the typical Funing soft clay along the Yancheng section of Phase II of the Huaihe River to Sea Waterway Project. A comprehensive experimental program combining XRD and SEM microstructural analyses with macroscopic geotechnical tests is conducted to examine the microstructure, one-dimensional consolidation behavior, stress coupled hydraulic conductivity, and creep characteristics of the soft clay. The study focuses on the effects of soil structure, thin interbedded sand layers, and hydraulic gradient on its permeability. The results show that Funing soft clay exhibits pronounced structural degradation and stress sensitivity during consolidation. The coefficient of consolidation, secondary consolidation coefficient, and hydraulic conductivity vary nonlinearly with increasing consolidation pressure and are strongly influenced by the preconsolidation stress. Under the same void ratio, the hydraulic conductivity of undisturbed clay is 3-4 times greater than that of remolded clay, and the difference becomes smaller with increasing consolidation pressure. The presence of thin sand layers reduces the sensitivity of permeability to consolidation pressure, resulting in a smaller decrease in hydraulic conductivity compared with pure soft clay. This suggests that thin sand layers play a regulatory role in local drainage and stress redistribution. Increasing the hydraulic gradient from 19 to 152 causes a slight reduction in the hydraulic conductivity of undisturbed clay, generally within 10%, indicating that the seepage structure remains relatively stable under higher gradients. The permeability values obtained from variable head tests, stress coupled permeability tests, and back-calculation from one-dimensional consolidation are in good agreement, confirming the reliability of the experimental results. Overall, the permeability of Funing soft clay is strongly governed by soil structure and stress history, while thin sand layers and hydraulic gradient act as important modifying factors. The findings provide a scientific basis for seepage control, settlement prediction, and foundation treatment in embankment engineering overlying soft clay in the Yancheng-Funing region.