Curtain Grouting, a Tool Used for Stopping the Seepage from an Existing Dam

摘要

Hidkal dam, also known as Raja Lakhamagouda dam, was constructed in the year 1974 across the river Ghataprabha in Krishna River Basin. In this dam, there are two dykes-Dyke I and Dyke II, each of length 5227 and 506 m, respectively. After impounding the dam, it was observed that there is seepage at a distance 3 km downstream of Dyke I. To overcome the situation, seismic refraction studies in the upstream of Dyke I were conducted by CWPRS, Pune, for delineating the stretch of the seepage zone. After identifying the seepage zone, trial boreholes of Nx size were made to determine the permeability of the strata for designing effective treatment measures. Recovery of material from the trial boreholes was examined to identify the rock type met with in the foundation along with the degree of weathering. The rock extracted is Deccan Trap Basalt with various degrees of weathering ranging from highly weathered to disintegrated variety including the presence of quartzite. The permeability values vary between 26 and 498 Lugeons. So to make the strata impermeable, curtain grouting was carried out in three rows, 1.5 m apart from each other from Ch. 4650 to 5330 m near the upstream heel through Nx size borehole. The spacing of the boreholes is 3 m c/c, and boreholes are staggered and up to depth of 20 m are suggested to be carried out. During the grouting process, CWPRS engineers inspected the process of grouting from bottom of borehole to the surface. After the completion of grouting, post-permeability tests were conducted and it was seen that the permeability values had drastically reduced. The data obtained during investigations were used in the preparation of a mathematical model (FEM). After the seepage analysis of the model, it was observed that there was drastic reduction in the seepage.