Types of Sheet Piles Cofferdams
Sheet piles are widely used for cofferdams due to sheet piles structural strength, interlocking capability that provides a water tight system.
Sheet piles are preferred too due to their ability to penetrate many types of ground.Thus achieving deep penetration which provides resistance to inward movement at the bottom of the excavation.
The ability to achieve deep penetration in permeable soil also has the advantage of cutting off water infiltrating into the excavation.
Most common available sheet piles can be used, sheet piles like the Larssen and Frodingham are widely used to form cofferdams. In fact, some contractors combine the different sheet piles utilizing the strength of each types/make of sheet piles to achieve an effective cofferdams.
Figure 1 - Cantilever Single Sheet Pile Wall
Sheet piles cofferdams can be of many types depending on the construction requirement and site conditions. An example of a simple cofferdam can be just a single layer of sheet piles cantilever above the working area. Normally this is used in low water heads or the required excavation is not too deep. Such a cofferdam is shown in Figure 1.
Figure 2 - Single Sheet Pile Wall with embankment
Should deeper excavation be required, an earth embankment can be left in front of the sheet piles. This is shown in Figure 2. Single sheet piles wall can be strutted across to the opposite sheet pile wall to form an enclose working area. Fewer struts are used if excavation is not deep. On the other hand if deeper excavation is required, than more struts are used and the cofferdams had to be strutted at different levels too. This is shown in Figure 3.
Figure 3 - Strutted Single Sheet Pile Walls
When the excavation area is too wide for strutting, than a more massive cofferdams can be constructed by utilizing double layer of sheet piles wall. The sheet piles wall are tied together or can be formed into interlocked cellular cells with filled with rock debris or earth infill between the sheet pile walls. This form a massive self supporting cofferdams that can keep exterior water at bay and the working area dry for construction works. This is shown in Figure 4.
Figure 4 - Double Wall Cofferdams
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