Treatment of Seepage through Vendarasankulum Twin Reservoir in Eastern Sri Lanka - Cost Comparison of Alternative Techniques

The purpose of this study is to select a more effective technique from ‘upstream cutoff’ and ‘grouting treatment’ for the control of seepage through the Vendarasankulum reservoir. Using engineering judgment, empirical and theoretical knowledge, trapezoidal cross sectional dimensions of layers of different soil materials were determined. For example, the cross section at 490m (from left); SC layer on the U/S side slope has widths, 3m and 12m at bund top and bottom respectively; clay layer in the core has widths 12 m and 3 m at the top and bottom respectively. The effective fetch (1.72 km) and thereby the maximum wave height (0.84m) were computed in order to extract values for thicknesses of riprap (0.45 m) and bedding layer (0.30m). Grouting treatment involves clay-cement grouting in the overburden and 6m deep cement grouting in the rock, requiring a total of 296 grout holes. While the estimated cost of construction of the upstream cutoff is SLR 30.3 million, the same for grouting treatment is SLR 11.3 million, indicating the former option would cost 168 percent more. Therefore, grouting treatment is more economical and sufficient, although upstream cutoff could offer better seepage control.