1Chief Research Officer, Central Water and Power Research Station
2Joint Director, Central Water and Power Research Station
Online published on 14 September, 2012.
Signs of reservoir seepage in terms of water pool formation at downstream side of earthen Dyke-l of Raja Lakhamgowda reservoir of Hidkal Dam of Hukkeri Taluka in Belgaum, Karnataka has been reported to be persistent ever since the impoundment of reservoir. Insitu permeability studies have been conducted at five boreholes between Ch.4700 and 5100m located at the downstream toe of Dyke-l. Heavy water losses even in low pressures have been observed from various sections. In order to provide remedial measures to prevent foundation seepage, it was recommended curtain grouting on upstream side of Dyke-l near heel line for the zone vulnerable for seepage. Project authorities have carried out curtain grouting using cement up to a depth of 15m from Ch.4700 to 5100m. To check the effectiveness of grouting and to have comparison of permeability values between grouted and ungwuted portion, post-grouting permeability tests have been conducted, at about 50 percent of the pressure used during grouting, in seven boreholes at Ch. 4650, 4750, 4850,4950,5050,5150 m and 5250m, in which Ch.4650, 5150 and 5250m are the boreholes where grouting has not been carried out.
From the permeability test results in the grouted portion Ch.4750 to 5050 m, permeability is found to be varying from 4 to 10.92 lugeons. There is significant improvement in post grouting permeability values as compared to the values prior to grouting. The permeability results confirmed that the grouting was effective and prevented heavy water losses through the foundation. While grouting different rows of holes from Ch.4900 to 5100 the cement intake is less than 30Kg/m in three rows and just near to 30 kgfyn in two rows in-between 4900 to 5100m.In these cases the grouted area will correspond to 2 to 8 times of the borehole size. Borehole spacing within the rows and row spacing depend on the effective radius of grouting. Narrow spacing is to be selected when cement intake is less than 30Kgfyn. The already grouted stratum from chainage 4700 to 5100 m is not to be disturbed. The portions, which have high permeability values and not grouted yet, are required to be grouted to avoid any foundation deterioration. It can be grouted at borehole spacing of 1 to 1.5 m and row spacing of 1 to 1.5 m.
