Two-dimensional simulation of underground seepage in a dangerous piping zone of the Jingjiang Great Levee, the middle reach of the Yangtze River

Abstract

This case study simulated the seepage field at Yangjiawan using Visual Modflow software. The Yangjiawan area shows potential for dangerous piping along the Jingjiang Great Levee, on the north bank of the Yangtze River. The levee foundation sits on loam and fine sand strata and is covered with a clay layer and artificial earthfill. Ponds are present behind the levee, where piping occurs frequently. The authors analysed several models to simulate actual situations and to provide guidance for piping control. Assuming that the potential for piping increases with seepage and groundwater velocities, the models allow various engineered control measures to be assessed under different natural conditions. Parameters and features of the models included: different water heads, pressure-relief wells, seepage-proof walls, surface coverage, different hydraulic conductivities of the artificial earthfill, and pond levels during high river water levels. The results demonstrate the effectiveness of pressure-relief wells in preventing piping and also show that a decrease of the hydraulic conductivities of the artificial earthfill would reduce infiltration and seepage damage significantly, especially during high river water levels. Furthermore, pressure-relief wells and the reduction of hydraulic conductivities of artificial earthfill should prevent piping if ponds are present.