Secant Pile Wall Model with Partially Saturated Soil

The undertaking of deep excavations in areas characterized by high groundwater levels, industrial zones, and largescale projects involving massive structures presents significant engineering challenges. Secant pile wall techniques offer highly effective solutions in such conditions. These walls are constructed using a combination of reinforced and plain concrete piles installed in an overlapping arrangement to form a continuous barrier that retains the surrounding soil and prevents collapse. The importance of secant pile walls lies in their high capacity to resist lateral earth pressures and control groundwater infiltration, making them a critical component in deep-excavation projects. Understanding the behavior of these walls, particularly under varying groundwater conditions, is essential to ensure their performance and stability. The dewatering process, which lowers the groundwater level, has a considerable impact on the deformation and stability of secant pile walls. Therefore, it is crucial to implement these systems in a manner that aligns with the excavation method and site-specific conditions to ensure structural safety and project efficiency. This study aims to investigate the behavior of a secant pile wall model when it supports sandy soil and is subjected to different water levels. This type of wall is commonly used in permeable sandy soils with high water content. As is well known, the excavation process is carried out gradually, accompanied by dewatering to prevent water from seeping into the excavation area. Therefore, we adopted an excavation and dewatering system that corresponds to the actual site conditions. The study looked into several different excavation depths on the passive side, including 0m, 0.2m, 0.4m, 0.6m, and 0.8. Moreover, water levels at different excavation depths (0.0, 0.2, and 0.4m) were measured Several parameters were evaluated, including the lateral total stress on both sides of the wall, horizontal and vertical displacements, and matric suction about the moisture content in the soil above the water level. According to the test results, the water level significantly influences the values of the lateral total stress. A decrease in the water level leads to a decrease in the amount of active total stress, while an increase in the magnitude of passive total stress occurs. Furthermore, lowering the water level causes a more substantial vertical displacement than a horizontal displacement at the top of the wall. The results indicate that lowering the groundwater level enhances the stability of the secant pile wall and increases the overall safety of excavation activities. However, this reduction in water level also leads to vertical settlement in nearby foundations. For example, when the water level is lowered from 0.2m to 0.0m, the vertical settlement increases to 0.25 mm at an excavation depth of 0.2m, while the horizontal displacement at the top of the wall remains unchanged at zero. This highlights a critical consideration for projects located near existing structures, as lowering the water level can induce settlement even when lateral movements are minimal. Keywords: Secant pile wall, Dewatering, Lateral stress, Lateral displacement, Vertical displacement, Soil water characteristic curve