Theory of Combined Seepage Applied to Dewatering Systems

Abstract

In the present study, an analytical solution is presented to solve the problem of combined seepage, under a sheet piling cofferdam, applied to dewatering systems. Existence of the sheet pile creates a confined seepage followed by an unconfined seepage in the same field, which presents a combined seepage problem. Two equations were developed to analyze the combined seepage underneath a sheet piling wall. Using such equations, both the maximum height of the free surface just behind the sheet piling cofferdam ( H o ) and the quantity of seepage discharge to be pumped out from the construction site ( q ) can be determined. The main parameters affecting the combined seepage characteristics underneath a sheet piling wall are: The depth of permeable foundation layer ( T ), the horizontal distance behind the sheet pile ( X ), the depth of excavation in the construction site ( D ), the embedded depth of sheet pile ( S ), the retained water head ( H 1 ), the accumulated seepage water depth ( H 2 ), and the side slope factor of excavation line ( M ). Study showed that, the above parameters have a great effect on the combined seepage, but with different extents.