Abstract：Abstract：Xinguang bridge project is the pivotal project of Xinguang throughway，and it will be the longest half-through arch bridge with three continuous spans in the world. The constructions of piers No.5 and No.6 meet much difficulty in this project due to the large-span，deep water，and intricate geologic conditions as well as water inpouring into hardpan in their sits. On account of all those factors，cofferdam with steel sheet pile is employed in this project with large dimensions，which is the largest steel sheet pile cofferdam in deep water in Guangdong Province. However，successful implementation of this project lies in how to solve the permeating problems of steel sheet pile cofferdam. As to the permeability problem，the formula for the equivalent permeability coefficients is modified. On basis of this modified formula，a variety of the equivalent permeability coefficients is modified during the self-healing up process of the steel sheet pile in the sandy layer are analyzed；and the calculation of the final seepage quantity as well as an estimation of the initial quantity of the pumped water are presented Moreover，it is concluded that permeability below the root of steel sheet pile will not cause seepage failure but only increase the leakage，which is confirmed by the two-dimensions finite element program on horizontal plane. Eventually，corresponding settlement was generated after a full account of both the merits and demerits of the cofferdam base in both draining and blocking up approaches. This project was completed smoothly，and complementary supporting evidences of the self-healing process of the steel sheet pile were deduced.
