Different filter design criteria and their applications to reservoir design in mountainous areas of southern Ningxia

Seepage is one of the main causes of embankment dam failures, whereas the seepage failures in hydraulic structure can be prevented by reasonable installation of filter layers. For the purpose of evaluating the effectiveness of protective filters for the loess base soils by using different filter design criteria, and finding out an appropriate one for the hydraulic structures in the loess hilly mountainous area, this paper takes the embankment dam filter system of Qiaojiagou reservoir in the mountainous area of southern Ningxia as an example. Four different grading curves were chosen from those paralleled grading curves within the upper and lower envelope of the actual filter material grading curves, whereby the characteristic particle sizes of the these curves and base soil curves were calculated. Then seven filter design criteria were applied to these grading curves and their applicability to the project was analyzed. The results show that with respect to the silty clayey loess acting as protected base soil, the current Chinese filter design criteria Design Code for Rolled Earth-Rock Fill Dams (SL 274—2001) has a broad application range and an excellent performance within the upper and lower envelope of the grading curve of the filter material in Qiaojiagou reservoir project, meanwhile the filtering and draining conditions are satisfied well.