MODEL TESTS ON SAND BOILING AROUND COFFERDAM CONSIDERING THE EFFECT OF GEOMATERIAL PROPERTIES
Keywords:Cofferdams, Seepage failure, Scaling model test, Scale effect
Cofferdams are widely employed for constructing structures in rivers and under groundwater tables. However, coffers constructed with sheet piles sometimes destabilize owing to sand boiling due to excessive upward seepage force inside cofferdams near the sheet piles. Therefore, a rational design method for cofferdams is indispensable for ensuring the reliability of the structures resting on the integrated foundation ground, even in water. Particularly the integrity of the foundation ground inside the cofferdam is examined by assessing the balance between the weight of the ground material and the upward seepage force, where the mechanical properties of the ground material or the scale effect of soil particles need to be sufficiently considered. In this study, we conducted a series of model tests on sand boiling occurrence inside a cofferdam. Two cofferdam models of different sizes were prepared, and several ground materials with different grain-size distributions and relative densities were employed. We analyzed the seepage flow process until sand boiling in every model test and determined the seepage flow condition for sand boiling and ground formation after failure. Consequently, we determined the perceptible effects of the mechanical properties of the ground material and the scale of the model cofferdam on the critical seepage condition for sand boiling failure.