Relationship Between Minimum Creep Length and Maximum Exit Hydraulic Gradient in Sheet Pile Cofferdams

Sheet pile cofferdams are temporary structures used widely to support the excavation pits in sandy soils. Double-walled and circular cofferdams are two of the commonly seen cofferdam shapes. One of the main concerns pertaining to these sheet pile cofferdams is the excavation base stability against piping failure. Factor of safety against piping failure of cofferdam structures in a sandy soil is the reciprocal of the maximum exit hydraulic gradient, assuming the critical hydraulic gradient approximately equals unity. Therefore, in this study, through a series of finite element simulations, simple expressions are developed and validated to estimate the maximum exit hydraulic gradient for both double-walled and circular cofferdams considering only the shortest seepage path, known as creep length. The proposed solutions, including mean, lower and upper bound values for the maximum exit hydraulic gradient at a given creep length can be used as the first-order approximations in ensuring the safety against piping.