Mullaperitar Dam- Remedy

MULLAPERIYAR DAM – REMEDY

Fatigue is a natural phenomenon for both living & inanimate things. The structures also get fatigued due to aging. Normally structures have a designed useful life. Beyond the designed life of any structure, constant vigil is to be exercised to check up any deterioration in the ability of the structure to withstand the designed job of that structure.
In the case of the Mullaperiyar dam, it is an old dam constructed with Surki mortar in the 19th century during the British rule. This “Gravity dam” is supported on its own weight against the pressure imposed on it by the impounding water in the reservoir. The pressure of water is concentrated on the Dam at its 2/3rd height above floor level. The principle is that the over turning effect (Upsetting Couple) of the Dam against the water pressure must counter balance by the (Restoring couple) acting at the centre of gravity of the Dam. If the Upsetting Moment is higher than the Restoring Moment, then the Dam is exposed to danger by overturning. Therefore the restoring couple or Moment must be greater than the upsetting couple or Moment. To attain this, the design is taken care of to see that the Resultant thrust of water & the weight of Dam is kept ALWAYS WITHIN THE MIDDLE THIRD RULE. That is the resultant line of force should be within the middle third of the base of the Dam.
The authorities must immediately check the stability of Dam and ensure that the Gravity Force of the dam is greater than the impounding pressure of the water in the reservoir. If the restoring Moment is not sufficient the dam must be strengthened by additional masonry structure at the tail race by widening the base width and masonry stem up to the 2/3 height.
Another aspect to be checked is the strength of the dam against shear force acting at the 2/3rd height. This strength may be low as the Dam is very old. To increase the shear strength of the structure, pressure grouting of the dam with high grade cement must be done at suitable spacing with modern equipments under close supervision by experts specialized in such critical jobs.
But there is no need to get panicky about life of the people around if the present water level is brought down to a safe level as suggested by the Engineers.

M P Abraham IRSE (Retd)
Chartered Engineer & Registered Valuer