DESIGN CHARTS FOR DOUBLE-WALLED COFFERDAMS

The problems of steady seepage into long double-walled cofferdams in a pervious stratum of finite depth were presented by King and Cockroft in 1972 for the cases of no excavation and full excavation inside the cofferdam. In 1992, Banerjee and Muleshkov presented the details of the exact solutions of the complete problem, including the special cases for which solutions were developed by King and Cockroft in 1972. These solutions have been derived in terms of elliptic integrals of the first and third kind. The equations depicting the rate of seepage, the distribution of hydraulic heads on the various segments of the domain boundaries, and the exit gradients at the base of the excavation were used to prepare the design charts presented in this paper. An example problem illustrating how these design charts can be used to facilitate computation of the requited quantities including seepage rates factors of safety against basal heave, and piping have also been included.