Friday, January 13, 2012

Structural concerns of Mullapperiyar

SreeNair | 9:58 PM |

Structurel deficiencies

           Mullapperiyar built on the then medieval technology  has celebrated its 115 years of existence in the last February.The present dam has no homogeneity in the materials used.It is an assortment of different materials used to strengthen in the begone years.There are no expansion joints in the dam as being given to the present day Dams and it remains as a single block in its entire width.

Dam in the upstream face ie the storage portion was built in rubble masonry.(-cement was not in vogue those days) containing  a mixture of lime and Sukey.Next to it is a concrete of Sukey,lime and crumbs of stones followed by the rubber masonry of lime and Surky.Then a gap which is  not grouted.Finally,on the downstream face, the new concrete-depriving it the much wonted structural continuity .

Records say that when the  dam was  filled with water for the first time itself,it  showed dampness and many seepage's.Through this wet area it is estimated that 30 tons of lime are lost per year as conceded by the Tamil Nadu authorities.There are no provisions for drainage gallery,pipe wells for releasing inner pressure.In these dam models it is a criterion that there should not be any  pull on any side either in full water level or not.Several examinations suggested that Mullapperiar is subjected to these pulls  which make it abundantly clear that the dam is built with such abysmal standards.

The strength of a dam is decided by tests on the thrust exerted upward by water within and in the depths. No such tests were done at Mullapperiyar.A study has revealed that,when considering the ground movements and 100% upward pressure, accounted as per the Indian Standards, the pressure shall be 2.8 tons. Even in brand new dams built with modern technology and practices seepages appear.As per Tamil Nadu the leakage in Mullapperiyar is much less.

Mr.P.K.JayaChandran for Mathrubhumi in his report says:"There lies the doubt.While the masonry dams built with identical characteristics show more leakages,then how come an old Mullapperiyar crossing 115 years could show less leakage!"The water loss could be many folded as per experts.The loss cannot be detected as the water collected in the ungroutted empty spaces goes to the bottom and leaves out which can not be seen.

When a dam is built,before the work begins, normally the rocky bottom is strengthened by grouting or such other techniques -which has not been adhered to in the case of Mullapperiyar.Considerable quantity of water- is lost being drained through the cavities in the bottom and the ungrouted gaps in the new concreted portion ,through the heap of soil piled up in the bottom. Holes provided , in the new concrete 'prop dam'( built later to strengthen the dam- to take the trapped water getting collected inside the old dam and the new structure(prop)) - is being filled with the seeping in lime.Therefore t very little amount of water is reaching the gallery built in the new prop dam ,which TN claims to be a meagre 89 litre /minute.This is how TN braves on the low amount of lime loss.

Sri.M.K.Parameswaran nair ,the chairman of the special cell on Mullapperiyar remarks that it is insane to suggest that this is the total discharge of water leaking through the creeks on the wall and is against the technical sanity.If this state of affairs allowed to continue it shall tantamount to inviting danger to the dam.In such a scenario an earth quake of sufficient magnitude can unseat the dam.

Kerala has asked for isotope tests to find the water leak in the year 2004. Babha atomic research centre is competent to conduct such tests.But TN is yet to respond positively.It must be noted that the same TN were up in their arms to conduct the tests when it came to Aliyar.The empowered committee has directed the TN to conduct the tests but it is yet to be known that the report will be tabled before the reports of High Power Committee reaches Supreme Court.

The Hindu reports:The scanning of upstream side of the Mullaperiyar dam using a remote operated vehicle by the Central Soil and Materials Research Station on directions from the Empowered Committee of the Supreme Court had found serious damage to the masonry structure between 95 to 106 feet from the base of the dam, quoting Sri. M. Sasidharan a retired engineer who was observer of Kerala during the scanning."Apart from innumerable pot holes, crevices and other openings that were visible on the surface of the dam, the masonry cover provided at the upstream side of the dam was seen to have undergone a crushing between 106 feet and 95 feet throughout the entire length of the dam.The damage that the dam has undergone in between the above noted elevations is so severe that no amount of rectification can salvage the dam from a disaster. Even a medium nature of earth quake of four to five magnitudes (on the Richter scale) near the dam site can shake the already loosened masonry cover to a collapsible condition."

Further the scan results projected deterioration at all 34 sections of the dam from massive erosion of lime Suki mortar from the rubble joints; exposing huge voids, deep pot holes, wide open joints, deep crevices and hollowness on the upstream periphery of the dam.On most of the sections at this area, rubble was seen in a loosened condition, suggesting that the dam has undergone an irreparable damage.

Mr. Sasidharan said:"following recommendation of the Central Water Commission in 1979,The dam had undergone a crushing on account of the additional load of nearly 21.75 tons per feet applied on the top of the dam in the form of RCC capping as part of emergency strengthening measure. The pre-stressing done by cable anchoring through the upstream masonry portion might have loosened and damaged the masonry." Mr. Sasidharan told The Hindu that when the original case over raising of water level was argued before the Supreme Court, Kerala had failed to present the argument that the dam was structurally weak.

What it had presented was applicable to many other dams. In court records, the Mullaperiyar dam was stated as a masonry dam whereas it was a composite dam. The inner core (62 per cent) of the dam was constructed with hydraulic lime surki mix and its upstream and downstream sides with rubble masonry.

He said that no present day engineer would dare even in his dream to design and construct a dam using hydraulic lime surki mix, in the manner of Mullperiyar dam, as this hydraulic lime surki mix is a very weak and unsound material, especially to withstand earthquake forces and high water pressure when compared to dams constructed with rubble or concrete materials.30 tonnes of lime is lost per year through the process of leaching-as admitted by Tamil Nadu.If so the dam might have lost 2079 tones of lime up to 1965,in 69 years,is a simple arithmetic.To make good these losses,TN had made grouting with cement during 1932-35 and in 1965.This way the quantity of cement reached inside the dam is a mere 543 tonne which testifies there are abundant vacuum inside.This was the situation till1965.What could be the picture now!

Times of India Report:
"Underwater visuals recorded by a remotely operated vehicle (ROV) show a deep fracture along the entire 1,200 ft length of the dam's foundation. The dam has inclined inwards as a result.The visuals came from an inspection carried out by experts, including those from Tamil Nadu and Kerala, for the high-power committee set up by the Supreme Court to look into the stability of the dam.

The ROV inspection began on March 5, after dividing the entire structure into 23 sectors, and lasted nearly a month.The CDs have been endorsed by officials from Tamil Nadu and Kerala. They have signed the CDs, and have submitted them before the high-power committee appointed by Supreme Court. The CDs show a huge crack in the foundation of the dam running all along the span of 1200 ft. The Tamil Nadu officials are fully aware of it, one engineer from Kerala, who was part of the inspection team."

Times of India adds:The visuals recorded by the ROV have been transferred to 42 CDs which have signatures of engineers from both Tamil Nadu and Kerala governments. When contacted, a Tamil Nadu official, who had analysed the visuals taken by the ROV, refused to acknowledge the crack. "There are 15 CDs and we have analysed the visuals. The CDs have been endorsed by senior engineers of the Tamil Nadu government" the official said.

In the bygone years the Dam has stood umpteen tremors and pressures.Several efforts for strengthening the Dam was taken up on Mullapperiyar as being done elsewhere such as strengthening with cable,concrete capping in the top,a crutch in the rear with concrete.etc which has extended its life.
115 years have gone Will the dam live up to 999 years.

The materials were collected from the different articles appeared in National and regional languages and also  from the Internet.


 

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