Seepage control for Satpara dam, Pakistan

The Satpara dam project is an earth core rockfill embankment proposed over moraines in northern Pakistan. This paper presents a perspective of the proposed under-seepage control measures improvised in the dam design through landscape development and foundation conditions, highlighting the field observations and in situ tests. Details are presented of optimisation studies involved in the decision on a solution for the foundation treatment of the dam, comprising a combination of an impervious upstream blanket with a partial cut-off for effective under-seepage control. The dataset of recorded permeabilities from the field tests ranges from 0·001 to 0·000 000 1 m/s. Estimates of uncertainties in the recorded permeability values have been explored, based on both statistics and judgement. A foundation model has been developed in RockWorks, using the closest point algorithm. Multivariate sensitivity analyses with combinations of blanket thickness, cut-off depth and position were carried out in SEEP/W to establish a composite under-seepage control design for the permeable foundations. Due importance was given to the computed hydraulic gradients throughout the analyses, but the final, optimal solution also had to involve other practical considerations: the practical modes of failure and their consequences, remedial possibilities and the practical construction potential associated with the measures adopted for under-seepage control.