Centrifuge model tests on behavior of double sheet pile wall cofferdam on clay

The behavior of double sheet pile wall cofferdam on a thick clay deposit subjected to a flash flood was studied through a series of centrifuge model tests. In a rectangular container a thick layer of kaolin clay was placed on a layer of fine silica sand. The clay layer was prepared with a defined stress history. The model cofferdam consisted of two aluminum sheet pile walls, with tie rods at the top and ground level. After driving the sheet pile walls to the sand layer, the inside of the sheet pile walls was excavated and filled with the same silica sand as used in preparing the bottom sand layer. Under 70 g centrifugal acceleration, the clay deposit was consolidated under the load from the fill to a certain degree and then water was fed upstream of the cofferdam to simulate high floodwater until the water level reached nearly to the top of the cofferdam or large deflection of the cofferdam was observed. Various factors affecting stability of the cofferdam and mechanism of failure were examined. Stability of the double sheet pile wall cofferdam on a thick clay deposit was also compared with a cofferdam on the sand deposit. Test results implied that: (i) shear deformation of the fill dominates the failure mechanism of the cofferdam, (ii) as the width of the cofferdam increases, the water height at failure increases, (iii) the resistance against high water does not always increase with increasing the embedment depth, (iv) the degree of consolidation of the clay foundation affects the stability of the cofferdam, though degree of consolidation was simulated after construction of the cofferdam, (v) performance with respect to the mechanical behavior of a cofferdam in a sand deposit is better than that in a clay deposit, and (vi) both the upstream and downstream sheet pile walls in a clay foundation are subjected to almost the same flexural stress compared to the larger flexural stress in the downstream sheet pile wall in a sand foundation.