# Field and Numerical Investigation of Taihu Resort Cut Slope Failure in Suzhou, China
## 5 Simulation of Sequential Slopes under Excavation and Rainfall Scenarios
### Influence of Rainfall Condition on Slope Stability  
Previous Section 5.2 have demonstrated the stability analysis of the slope under excavation conditions based on stress and strain distribution. Section 4 investigated Taihu slope failure in Suzhou based on monitoring data. It became clear that heavy rainfall in June 2013 caused a significant failure in Section 6 (S6) of the Taihu slope. In this section, the finite element calculation models of the cut slope under rainfall conditions are established using Midas GTS. This would provide a feasible approach for a more accurate analysis of the effect of rainwater infiltration on slope stability. According to the field survey results of the landslide, considering meteorological data of the Suzhou area, two classified rainfall amounts are selected to determine the effect of rainfall on soil water retention and slope stability: 60 mm/day is regarded as moderate rainfall and 180 mm/day as heavy rainfall. In practical soil engineering implementations, the saturation and volumetric water content of soil often change due to the increase in rainwater infiltration, or other causes. Due to the unavailability of data on the volumetric water content of the slope, the influence of different rainfall intensities on the pressure head and slope stability factor are studied in detail. The rainfall infiltration based on the soil-water retention and tendencies of slope stability under moderate and heavy rainfall intensities were analyzed and compared. In order to study the extent of influence of rainwater infiltration on slope stability, a numerical analysis of the rainfall impact on the pore-water pressure of the slope under rainfall conditions was presented and analyzed. The influence of rainfall conditions on the simulation model was determined over 15 consecutive days of rainwater infiltration. These are presented in four steps: 1 day of rainfall, 5 days of rainfall, 9 days of rainfall, and 15 days of rainfall. The numerical simulation results of the pore pressure head are illustrated in the following figures. Figures 13 and 14 illustrate the distribution of the pressure head of slope induced under different rainfall intensities. During the numerical modeling, as illustrated in Figures 13a and 14a, the pressure head distribution within the slope depicts certain changes at the top and surface of the slope after one day of heavy and moderate rainfall. However, it can be observed that the pressure head is relatively small, including the contour of the pressure head that starts shrinking gradually into the slope body. With continued rainfall, rainwater infiltration influences the pressure head significantly, which continues to shrink after 5 and 9 days, respectively; as a result, the pore pressure distribution increases over time at the toe with the continuous rainfall infiltration. With the increase in groundwater  
Figure 12: Horizontal stress curves at different measurement points during excavation stages. (**a**) Selected point C (**b**) Selected point A.  
level of the slope after 9 days of heavy rainfall, the pressure head increased significantly at the toe surface of the slope, indicating that the toe of the slope was the first slope part eroded by rainfall. Similarly, this increased the slope's body weight, which affected the slope stability. Otherwise, the slope was unstable. After this, it can be noted that only a tiny part of the slope was observed in the pressure head distribution under heavy rainfall compared to moderate rainfall intensities. In this part, the unsaturated zone has shrunk considerably in a heavy rainfall scenario, and the pore water pressure area of the slope has expanded at the weathered argillaceous siltstone layer. This resulted in the front layer of the cut slope under heavy rainfall being severely less stable than when the slope was under moderate rainfall. Figure 13: Cont.