Due to climate change, higher rainfall infiltration is expected in the future and it may cause a slope failure. Simultaneously, infrastructure construction and urban redevelopment are rapidly generating large amounts of construction and demolition waste that also contributes to global climate change. To ensure the stability of the slope, it is important to find cost-effective and environmentally sustainable alternatives. Waste material such as recycled concrete aggregate (RCA) can be utilized to protect the slope. The use of RCA for slope protection is that it can be used as a material for the capillary barrier system. The objective of this paper is to investigate the characteristics of pore-water pressure distribution and slope stability with the application of RCA protection during rainfall in comparison with the original slope through numerical modeling. The SWCC for the soil and RCA materials were measured using a high-suction polymer sensor (HSPS) and Tempe cell, respectively. The volume changes of the soil were measured using 3D scanner. SEEP/W was used to conduct the seepage analyses and obtain the change of pore-water pressure distribution due to rainfall infiltration. SLOPE/W was used to evaluate the stability of the slope with different climatic conditions. The use of recycled concrete aggregate (RCA) for slope protection from rainfall infiltration has been investigated in this paper. The results showed that the safety factor of the slope increased with the addition of RCA protection. Rainfall infiltration causes a reduction in soil suction and hence reduces soil shear strength, the safety factor will also decrease since the soil will become weaker.

The occurrence of rainfall-induced slope failures has become more frequent due to the effect of climate change. Hence, various studies have been conducted to analyse the effect of rainfall infiltration on slope stability. Physically-based hydrological models have been commonly used with slope stability models such as the infinite slope model to develop slope susceptibility maps. However, a combination of three-dimensional (3D) water balance model with 3D limit equilibrium method (LEM) has not been commonly used. Hence, in this study, a water balance model, GEOtop was used to investigate the influence of subsurface flow in unsaturated soil under extreme rainfall conditions on regional slope stability in 3D directions. The results from the GEOtop model were used as inputs for 3D LEM slope stability analysis performed using the Scoops3D software to obtain the factor of safety (FOS) map for the region. Four slopes within the region were then selected to be modelled in the twodimensional (2D) seepage and slope stability analyses, SEEP/W and SLOPE/W. Results from the detailed study showed that the pore-water pressures (PWPs) from the 3D water balance analyses were found to be higher than the 2D seepage analyses. Under similar PWP conditions, the FOS from the 2D slope stability analysis was observed to be lower than the 3D analysis for two out of the four slopes. However, the combined 3D water balance and slope stability analyses produced lower FOS compared to the 2D seepage and slope stability analyses due to the higher PWPs in the 3D water balance analyses. Therefore, this study highlights the importance of considering the 3D subsurface flow in unsaturated soil given that it has a significant influence on the FOS of slopes.

In this paper, a computational framework based on the Smoothed Particle Finite Element Method is developed to study the coupled seepage-deformation process in unsaturated porous media. Governing equations are derived from the balance laws of solid and fluid phases considering partial saturation effects in porous media. Moreover, an hourglass control method is implemented to avoid the rank-deficiency issue in SPFEM and the moving least squares approximation technique (MLS) is implemented to eliminate the pore pressure oscillations when the low-order triangle element is used. The proposed coupled SPFEM formulation is validated through four elastic examples and one elasto-plastic example. Good agreement with the numerical or analytical results reported in the literature is obtained. Further, the rainfallinduced slope failure is studied, in which a suction-dependent elasto-plastic Mohr-Coulomb model is adopted to take account of the suction effect in unsaturated soil. The evolution of the suction and soil deformation during the rainfall period and the whole slope failure process are obtained. It is demonstrated that the proposed method is a promising tool in numerical investigations of both the triggering mechanisms and post-failure behavior of the rainfall-induced slope failure.