The Kerala government has filed an application in the Supreme Court to place on record the report of the Department of Earthquake Engineering, Indian Institute of Technology, Roorkee, that “both the main Mullaperiyar dam and baby dam are likely to undergo damage which may lead to failure under static plus earthquake condition and therefore needs serious attention.”
The application was filed on October 31 even as a three-judge Bench is hearing the dispute between Tamil Nadu and Kerala relating to raising the water level in the dam beyond 136 ft.
The study was conducted in two parts. Part 1 deals with the seismic hazard assessment and Part 2 deals with seismic stability analysis. In its conclusions and recommendations on seismic stability analysis, the report says “the earthquake safety of old concrete or masonry dams under moderate to strong ground motions is of great concern. Although there is no evidence of catastrophic failure of gravity dams in past earthquakes, the possibility of tensile cracking is never ruled out.”
“On the basis of the study, it is found that the static tensile stresses and combined static plus earthquake stresses at heel of the main dam exceed the average ultimate tensile strength of RR masonry (provided by the Irrigation Department of Kerala) and therefore the main dam during static plus earthquake (MCE/DBE) condition is likely to undergo damage.”
“The baby dam under static plus earthquake condition up to reservoir level of 155 ft is found to be safe. For probable maximum flood, which will cause reservoir level to rise up to 160.22 ft, the baby dam may undergo some cracks at the dam heel. Under static and earthquake loading conditions for Maximum Considered Earthquake (MCE), the tensile stress at dam heel exceeds the maximum apparent seismic tensile stress and therefore the random rubble masonry of the baby dam is likely to undergo damage.”
It said “most of the values adopted here for material properties are based on the tests conducted some 20 to 25 years back. During this period, this dam has definitely gone through considerable deterioration due to ageing and weathering. As such, the assumed parameters may be naturally higher than the in situ condition. Proper assessment of existing material properties is very important for the safety assessment. It is therefore recommended to carry out further testing on the dam and foundation materials.” Hearing resumes on Wednesday when Tamil Nadu will continue its arguments.
