Testing of Polavaram’s D-Wall to begin today; NHPC team arrives
Vijayawada: Tests to ascertain the structural stability of the nearly 700-metres long non-scoured and exposed portion of the diaphragm wall of the Polavaram irrigation project are being taken up from Wednesday.
Experts from the national hydroelectric power corporation arrived at the Polavaram irrigation project site on Tuesday for the tests. NHPC executive director L Kapil inspected the diaphragm wall and inquired about the preparatory works done by the water resources authorities for tests to ascertain the health of the diaphragm wall.
The team headed by the ED included A Vipul Nagar, NK Pandey and MP Singh. They would do tests of mainly electrical resistivity and cross-borehole tomography.
The plan is to have tests on the exposed portion of the diaphragm wall, out of a total length of 1,400 metres. With some 700 meters of diaphragm wall in two portions, like reach-1 and 2, having been scoured and submerged in the river water, there is no chance of any tests on it. This would be replaced with a fresh wall.
The water resources authorities are having two options. One, they would find out the health of the 700-metres portion of the non-scoured and exposed wall. If it is found healthy and intact, a fresh diaphragm wall of 700 metres would be constructed by replacing the scoured and submerged portion of the wall. This would be joined with the healthy diaphragm wall.
The second option is, if the non-scoured portion of the diaphragm wall is also damaged, there will be a new wall for the entire stretch of 1,400 metres and the existing damaged diaphragm wall would be turned into a dummy.
However, for construction of either a portion or the full length diaphragm wall, the state has to import construction equipment from Germany to construct a 1.5 metres-width diaphragm wall. No such equipment is available here. The width of the diaphragm wall is relatively high as against regular size of one or 1.2 metres. The maximum depth from where the diaphragm wall is to be constructed is nearly 100 metres. It takes nearly a year to take up the construction of the D-wall after mobilizing all the requisite equipment from Germany. This is expected to cost nearly 400-600 crore.
It takes nearly 45 to 60 days to conduct the tests on the D-wall. After that, a report has to be prepared and submitted for approval to the stakeholder agencies like the central water commission, the dam design review committee, the Polavaram project authority etc.
Polavaram project superintendent engineer Narasimha Murthy said, “The health assessment of non-scoured and exposed portion of the D-wall will be done via a series of tests from Wednesday.”
Infographics:
- The tests will help find any cracks on the existing D-wall and ascertain its structural stability.
- Joining of fresh wall to the existing wall is permitted at a length but no such permission will be given for height of the wall
- As the cost of construction materials has risen, a cost escalation is likely for construction of the D-wall
