The 3rd International Symposium on Life-Cycle Civil Engineering
OCT 03-06, 2012
Hofburg Palace, Vienna, Austria
The foundation of Ying-liang-bao gate dam consists of 5 layers of sand or gravel soils alternatively with a total depth up to 126.5 m. The seepage coefficient of gravel layers is more than 100 times that of sand layers. A concrete cutoff wall up to 80 meters depth is used in the first design scheme to control the seepage. Although the cross water head of the dam is only about 30 meters, the subsoil is susceptible to internal erosion. The calculated seepage field of the scheme indicates that the internal erosion risk of the sand layers is very high. The reduction of flux is not effective via the depth increase of the partially cutoff wall, unless the covering layers are cut off completely by a closed wall. Not only the internal erosion risk in the relatively impermeable layers is difficult to reduce via increasing the depth of a partially cutoff wall, but also the risk in the soils beneath the suspended wall increase greatly and thus jeopardizes the structure safety of the cutoff wall. The scheme with a closed cutoff wall is erosion safety and it is recommended to and adopted by the preliminary design. A scale reduced element is proposed to evaluate the appropriate position of the cutout boundary in the covering layers. It shows that the position of an imperious boundary has significant influence to the total flux of the foundation with alternatively strong and weak permeability layers.