KOCHI: The structural stability, strength, safety, height of water, effect of seismic forces, hydraulics, effect of leakage etc on Mullaperiyar dam are basically to be decided by expert civil engineers, IIT panels etc. It is learnt that in the report, the Empowered Committee has considered the reports by the civil engineers, IIT panels/technical bodies, technical members in the committee etc. Accordingly, the dam is safe and sound and the height of water can be increased.
However, I as a civil engineer am curious to know how the dam has been certified as safe and sound even when the height of water is increased. The contention that the 116-year- old dam made with surkhi morter has not suffered any loss of strength is not tenable. The dam is a straight gravity dam, and any civil engineer worth his salt knows that the ‘Middle third rule’ is applicable ( the resultant of the water thrust/lateral forces and the weight of dam should pass through the middle third of the base so that no tension is induced).
The safe height of water can be arrived at, by applying the ‘Middle Third’ rule. While applying the ‘Middle Third’ rule, a correction is to be applied to the base width considering the loss of strength over the years - ie, assume a lesser base width. The experts should be able to assume a suitable width. The strengthening done (anchoring, lining, capping etc) has a compensating effect and this also is to be considered.
In addition, the effect of earthquake is to be considered. The ultimate effect of the earthquake is to cause a lateral force which will also increase the possibility of failure. The permissible height of water, thus calculated by applying the ‘MiddleThird’ rule, may be less than the present height of water permitted and this is the reason for my curiosity. I will be very glad if I am proved wrong.
Beyond a point, increasing the height of the water increases the possibility of failure. There are other points also to be considered like sliding, overturning, compressive strength of masonry etc. I have not seen any of the reports. I am sure that the above points would have been considered. With all respects to seismologists, it may be pointed out that they cannot certify a dam as safe against seismic effect.
It is the civil engineer who checks the structural stability of the dam against seismic forces (Indian Standards, IS.1893) and certifies it. The role of the seismologists is to advise on the seismicity (liability to or frequency of earthquakes), the intensity etc. Technical matters should be decided by technical experts and not by jurists. The jurists should confine themselves to legal matters.
(The author is former DGM, Kochi Refineries Ltd. Ph : 0481 2570312 / 9447567671. The views in the article are the writer’s own).