Research on Deformation and Seepage Properties of Larsen pile reinforcing cofferdam based on numerical analysis, Tianjin, China

The implementation of cofferdams in hydraulic engineering has consistently represented critical yet challenging components of construction projects. A well-engineered cofferdam can effectively reduce overall construction difficulties and ensure construction safety. In this study, a cofferdam repaired from a field ridge on a river was used as an example; numerical simulations combined with the limit equilibrium method were employed to assist in designing the cofferdam and lowering the groundwater table to ensure the project's economical safety. Larsen-pile steel sheet piles are employed to reinforce the field edge. The methodology utilizes the coupling of effective stress with seepage fields, incorporating both saturated and unsaturated conditions in soil with elastic-plastic properties. The results validate the effectiveness of the methodology through monitoring data. Our research reveals that the values and variations of vertical displacements at the top of the piles from the simulation are approximately consistent with the monitoring data during the lowering of the groundwater table, affirming the methodology's reliability. The simulated results indicate that while soil filling on both sides of the cofferdam underwater does not significantly contribute to pile top settlement, filling at the top induces greater settlement. Additionally, the higher density of the piles leads to a slight overall increase in soil vertical displacement, with significant variations near the piles due to their higher elastic modulus. Furthermore, the remarkable seepage control efficacy of the Larsen steel significantly lowers groundwater table downstream and reduces the hydraulic gradient of the flow field, thereby enhancing the stability of the downstream slope. Our result suggests that effective seepage control and geodetic monitoring may be an effective measure to enhance the stability and integrity of earth-rock cofferdams in hydraulic engineering projects.