Medigadda barrage is safe, declares experts

The Medigadda Barrage, part of the Kaleshwaram project, is confirmed to be safe except for the seventh block. On the evening of May 23, a loud noise was heard when gate number 16 was lifted, and a large hole appeared in front of the 20th pillar, seemingly below the barrage. This incident caused a widespread concern, but engineers have refuted claims of extensive damage.

An expert committee clarified that the noise and supposed chasm were exaggerated. They explained that due to an error with the secant piles, sand under the seventh block’s foundation washed away, leading to the collapse of the 20th pillar. This resulted in a void under the seventh block but not a chasm, and no other technical faults were found in the barrage.

These findings came from Electrode Resistivity (ERT) and Ground Penetrating Radar (GPR) tests conducted by the Barrage Construction Agency. The authorities assured that temporary usage of the barrage is possible through sand and cement grouting. The National Dam Safety Authority (NDSA) expert committee has recommended several protective measures.

The Medigadda Barrage consists of eight blocks and 85 gates. Engineering authorities have initiated steps to investigate the collapse of the 20th pillar in the seventh block. The construction agency L&T and IIT Roorkee are involved in this process.

Initially, ERT was performed on the seventh block to assess the underground conditions based on electrical resistance, which varies in different materials like sand, water, and metals. Following this, GPR was used to examine the physical condition underground, identifying soil layers, material properties, changes, cracks, and voids. These tests confirmed that all blocks, except the seventh, are safe.

Under the foundation of the seventh block, a void of 1000 cubic meters was detected. Secant piles are intended to prevent soil erosion due to internal water flow, but a defect at the 20th pillar of the seventh block caused water to erode the sand and soil, creating a gap and leading to the pillar’s collapse. Officials state that this issue can be resolved by filling the void with a cement and sand mixture.

While the construction agency conducted ERT and GPR tests, the Irrigation Department plans further studies on the barrage’s technical defects based on NDSA expert committee recommendations. They are consulting with organizations such as CWPRS, CSMRS, and NGRI, with a team from NGRI expected soon.

The NDSA expert committee’s interim report has prompted irrigation authorities to take protective measures for Medigadda, Annaram, and Sundilla barrages. These include lifting the gates of the 20th pillar and adjacent pillars, grouting the void under the foundation, initiating boreholes at the top of the raft, and restoring CC blocks above and below the barrage. Temporary protective measures will be in place during the rains.