The soilbags reinforcement has been widely used for soft soil foundation improvement due to its high compressive strength and deformation modulus considering the time limit of many projects and the characteristics of the reclaimed soil. However, despite the strength and deformation properties of soilbags reinforcement, the drainage characteristics of soilbags reinforcement is a crucial factor that creates a large challenge to foundation improvement for soft soil. Thus, this study developed a four-staged surcharge preloading on soilbags-reinforced soft soil foundation and focused on its drainage consolidation effectiveness. The contrasting laboratory tests were performed in four identical experimental boxes with clayey soil from the Nanjing, China. Four-staged preloading were applied on the soilbags-reinforced testing model, respectively, the data of the settlement and water discharge during the test are monitored, and after the tests, the water content and shear strength at different positions are measured. And three contrasting tests considering the possible drainage channels of soilbags reinforcement were also conducted. The results show that the consolidation effect is achieved with the soilbags reinforcement in terms of the settlement, pore water pressure, water content and shear strength after consolidation.

In this study, we perform a stability analysis on three-dimensional (3D) geosynthetic-reinforced soil structures (GRSSs), focusing on their response to varying rainfall conditions. The magnitude and distribution of pore water pressure in unsaturated backfills throughout the infiltration event is calculated to determine the time-dependent matric suction and apparent cohesion in backfills. An analytical expression representing the necessary strength for geosynthetic reinforcement in 3D GRSS is derived from the energy balance equation, utilizing the kinematic limit analysis approach. The validities of both the necessary reinforcement strength and the pore water pressure distribution are confirmed in this study. Further exploration is conducted into the effects of the 3D geometric features of the GRSSs, the effective cohesion and friction angle of backfills, alongside factors related to rainfall intensity, duration and patterns. These considerations influence both the required reinforcement strength and the failure pattern of the GRSSs. The findings indicate that the necessary reinforcement strength and critical failure pattern of a GRSS are dictated not only by its 3D geometric properties but also by the unsaturated soil mechanics and the nature of the rainfall it encounters. An identical accumulated rainfall will result in approximately a same required reinforcement strength solution of GRSS after rainfall. This study provides guidance on preliminary design of GRSSs under rainfall conditions.

To provide new insights into the liquefaction and post-liquefaction behaviors of calcareous sand with and without geosynthetics reinforcement, a series of multi-stage cyclic triaxial tests were conducted. The geosynthetics employed in this study include geogrid, geotextile, and geotextile-geogrid composite. The multi-stage tests consist of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading without excess pore pressure dissipation. The effect of different arrangements of reinforcement layer on the behaviors of calcareous sand is examined and discussed in this study. The test results indicate that a unique relationship can be observed between the double amplitude axial strain and the pore pressure ratio of calcareous sand, irrespective of the influence of reinforcement layer arrangement, providing an effective means of predicting the strain at a given pore pressure level. The liquefaction resistance of calcareous sand increases with the increase in the number of reinforcement layer and decreases with the increase in the distance from the first layer of reinforcement to the sample's top surface. Compared to geogrid and geotextile, the proposed geotextilegeogrid composite exhibits better efficiency in enhancing the liquefaction resistance of calcareous sand. The reinforcement also accelerates the recovery of strength for liquefied calcareous sand and increases the maximum shear strength of sand at large axial strain during the post-liquefaction stage.