Amidst the cacophony over the safety of the Krishnaraja Sagar (KRS) dam due to stone mining in close proximity, a retired engineer from the State government has also expressed concern and raised technical points germane to the issue.
B.S. Balakrishna, a former Superintendent Engineer of the PWD, who has worked on numerous projects of State importance, said that there are ample studies published on the impact of blasts and explosives on the stability of dams.
The process
He said blasting is required to remove in-situ blocky hard-rock material and this causes seismic wave propagation. The energy propagated through the earth body then produces vibrations in the rock mass and the intensity or level of the vibration varies depending on a blasting design and geological setting, said Mr. Balakrishna. With reference to the KRS, he pointed out that the dam has been constructed of masonry and earthen embankment and not of RCC and hence it was more susceptible to shock waves.
Mr. Balakrishna said the possible impact of a blast on any infrastructure can be assessed by simulating the seismic load and pointed out that a technical study conducted in the United States of America on the effect of mining operations indicated clear danger to many of the existing structures.
He said the application of blasting methods should take into consideration the rock condition and the terrain. In case of blasting relatively close to the dam, the vibration could cause damage to the dam due to the seismic effect as a fallout of the blast.
Notwithstanding the claims of political leaders that the dam was safe, Mr. Balakrishna said it is extremely tough, even for top experts in the world, to vouch for the safety and life of old bridges and dams. Citing an example, he said that a team of experts from the Union government inspected the old Mondavi bridge for three days and gave a certificate in writing that the bridge was safe.
Allaying fears
Meanwhile, Cauvery Neeravari Nigam Ltd. has vouched for the safety of the dam to allay public fears. Engineers attached to the State government have also said that the KRS was undergoing a major rehabilitation exercise and 136 of the sluice gates are being replaced with World Bank funding.
An exercise of such a magnitude entails a detailed study of the present condition of the dam, said the officials. Innumerable technical committees and engineering experts visited the dam to assess the safety of the structure before giving the go ahead for gate replacement, they added. Besides, certain interventions to strengthen the dam and enhance its lifespan was also suggested and were implemented, according to officials.
