Effect of soil consolidation on the interface direct shear behavior of excavated clay soil reinforced with a geocomposite drainage layer

Landslide disasters have occurred at excavated soil dumpsites in China’s soft soil regions due to poor drainage and weak strength of clay soil. A potential solution is a geocomposite drainage layer (GDL), which drains and reinforces the soil. Understanding the consolidation effect on the shear behavior of clay soil-GDL interfaces is vital for using GDLs in dumpsites. Large-scale interface direct shear tests were conducted on excavated clay soil (a common type of excavated soil in China’s soft soil regions) and three geosynthetics (GDL, nonwoven geotextile, and geogrid) under different normal stresses and consolidation degrees. The results showed: 1) The shear curves of clay soil-GDL interface were strain-hardened and were significantly affected by the soil consolidation. A consolidation-dependent shear constitutive model was proposed and can accurately describe those shear curves. 2) The shear strength envelops of clay soil-GDL interface satisfied the Mohr–Coulomb failure criterion. As the soil consolidation degree increased, the cohesion c exhibited a slight linear decrease, i.e., c(U) = –1.128U + 6.487, whereas the friction angle φ showed rapid linear growth, i.e., φ(U) = 10.300U + 2.685. 3) The significant increase in shear strength of clay soil-GDL interface during soil consolidation is primarily due to the improvement in soil shear strength and the “dimple effect” occurred in the interface. 4) When the soil consolidation degree exceeded 30%, the reinforcement efficiency of the clay soil-GDL was superior to that of the clay soil-geotextile and unconsolidated clay soil-geogrid. These findings shone a light on the confidence of using GDL as an efficient tool to improve the stability of excavated clay soil dumpsites.