VIJAYAWADA: Works to fill up the scour pits between the two cofferdams, where the earth-cum-rock fill (ECRF) dam of the Polavaram Irrigation Project is to be constructed, commenced on Wednesday.
Following the approval of the Dam Design Review Panel, the works were taken up. Polavaram project officials, engineers of MEIL, the project executing agency, and other officials performed puja before commencing the sand filling of the scour pits at three places.
“Nearly 10 lakh cubic metres of sand is required to fill up one scour and nearly one month is needed to complete it. There are three scours between Gap 1 and 2. The scour pits are expected to be filled by the end of April and thereafter vibro compaction will be done to strengthen the area,” Polavaram project Chief Engineer B Sudhakar Babu told TNIE.
After the sand is filled in the scour pits, which are so deep that even a 10-storey building can be kept in them, the vibro compaction method will be used to strengthen the filled portion of the area.The entire area will be divided into a 50x50 grid for the propose. Already two rigs are stationed at the project site and another five rigs are being brought by March 20.
“The scour pits are at the depth of -10 to -12 level and they have to be brought to +14 level, that is river bed level. On an average, difference of 20-23 levels have to be covered before taking up construction of a new diaphragm wall,” he said.
During 2019-20 floods, diaphragm wall of the Polavaram project was damaged. Out of 1,400 metres length of the diaphragm wall, 180 metres extent was damaged on the left side and around 200 metres on the right side. “We have to construct another diaphragm wall parallel to the damaged portion of the D-wall. It should be more than what was damaged. We will be constructing around 500 metres of parallel D-wall in parts covering the damaged portion. This will be carried out after firming up the river bed, where it was scoured during the floods,” he explained.
All the works, including sand filling of the scoured area, vibro compaction and construction of parallel D-wall are estimated to cost an additional Rs 2,000 crore. As care has to be taken for the quality of the work done and test the compactness of the filled portion of scour pits from time to time, construct D-wall, taking the rains and floods during the monsoon into consideration, the project construction in its entirety may get delayed. The project is supposed to be constructed by March 2024.