A simple cofferdam is constructed by installing two long parallel sheetpiles in a river bed as shown in Fig 3. Dimensions are in meters. Between the two sheetpiles, water will be pumped out to prepare an area for construction of a bridge column. Outside the cofferdam, the water level is estimated to be 1.6 m. A seepage analysis is necessary to find out the required pumping capacity and also to assess the stability of the sheetpiles. A numerical analysis using finite element method is conducted and a group of contour lines for different pressure heads (equipotential lines) within the permeable area are calculated and reported in Fig 4.

Requirements

You need to use this preliminary numerical result to:

B1. Complete the flow net.

B2. Calculate the seepage rate and the required pumping capacity [Volume/Time] for every meter

of the cofferdam. Assume a hydraulic conductivity of k = 0.027 mm/sec for the soil.

B3. Sketch the water pressure distribution on both sides of both sheet piles.

B4. Calculate the magnitude and location of the resultant force caused by water pressure on both

sides of both sheet piles. You need to calculate the location and magnitude of one force for

each side of each sheetpile (i.e. four forces altogether).

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