Road caves in on Cherthala NH overbridge, leaving 4-metre-deep crater; major tragedy averted

Alappuzha: A massive sinkhole formed on a newly constructed National Highway overbridge at Cherthala in Alappuzha district after the soil beneath the road caved in, raising fresh concerns over the quality of construction on the highway.

The incident occurred around 6 pm on Tuesday on the overbridge at Eleventh Mile on the Alappuzha-Thuravoor stretch of the National Highway. The crater, estimated to be about four metres deep, appeared shortly after a bus and a car had passed over the bridge. A major tragedy was averted after a motorcyclist noticed the road beginning to cave in and stopped his vehicle. Other motorists also halted their vehicles, preventing further traffic from entering the affected stretch.

Authorities attempted to fill the crater with sand on Tuesday night, citing the need to prevent further collapse. However, local residents blocked the work, demanding that the District Collector and senior officials of the National Highways Authority inspect the site before any repair work was undertaken. They also sought assurances regarding the safety of the bridge.

The overbridge had recently been completed and partially opened to traffic, with vehicles using the route for the past several days. Preliminary assessments suggest that continuous heavy rain washed away the soil beneath the structure, leading to the collapse. Residents also alleged that a pipeline belonging to the Japan Drinking Water Project, which runs close to the road, had burst about a month ago, causing significant soil erosion. They claimed this may have contributed to the formation of the sinkhole.

Fresh concerns over construction quality
The incident has reignited concerns over the construction methods adopted for the Alappuzha-Thuravoor section of the National Highway.

The grievances were previously raised against the practice of laying interlocking bricks in just a single row on the sides and filling the rest with sand. Previously, during rains, soil erosion had occurred through the gaps of these interlocking bricks on the sides of the flyovers at areas like Thiruviha, Arthunkal Bypass, Thankikavala, and Vayalar Junction in the district. Locals had also filed complaints with the Water Authority and the District Collector against the construction, pointing out that the bricks were laid directly over drinking water pipelines without even relocating them.

Residents also blamed the authorities for failing to properly monitor the newly opened stretch despite persistent heavy rain. They alleged that no inspections were carried out to assess the risk of soil erosion or road subsidence, even though such possibilities were foreseeable during the monsoon. The incident, they said, has further eroded public confidence in the safety of the highway.

Questions over soil used for construction
The collapse has also renewed debate over the quality of soil used for the National Highway project. According to residents, sand dredged from Vembanad Lake was used between Thuravoor and Paravur, while sand from Thottappally was used between Paravur and Kottukulangara after shortages of conventional fill material slowed construction.

Experts had earlier expressed concerns over whether the dredged sand, which is silty, saline and contains shell fragments, would be suitable for road construction under Kerala's climatic conditions. Reports had stated that such material was unsuitable for structural construction and should only be used for land filling. However, based on recommendations by the Kerala Engineering Research Institute, the material was permitted for use in the National Highway project under specified conditions.