Abstract：Mengkuang Dam in Malaysia has a foundation filled with residual soil of weathered granite. The exploration indicates that the permeability index for dam foundation has great dispersion，drawing the conclusion that the dam foundation soil has small permeability and anti-seepage treatment is not required. However，seepage appears during the reservoir operation. After the project upgrading，it is difficult to make assessment on foundation permeability only based on the results from field test. In this article，inversion analysis is conducted to ascertain the permeability coefficient for dam body and foundation based on the measured data. Through the analysis，permeability indices for dam body and foundation conforming to the observation are obtained，providing main basis for engineering design and showing the reason for dispersion of exploration result. Parameters from inversion analysis are used for permeability prediction and assessment on dam seepage quantity and dam foundation seepage stability after upgrading，drawing the conclusion that the dam seepage quantity after upgrading is large. The requirement for dam foundation seepage stability can not be satisfied and anti-seepage treatment is required. With respect to the real situation of the project，the anti-seepage scheme is proposed.
