Alappuzha: The massive sinkhole that formed on the National Highway at Cherthala has been filled using a concrete mixture, even as officials prepare to inspect the site to determine the cause of the collapse.

The crater, which was about 4 feet deep, is believed to have formed after the sand beneath the road was washed away. Officials from the National Highways Authority of India (NHAI), the Public Works Department (PWD) and the Alappuzha District Collector are expected to inspect the site on Wednesday.

The sinkhole appeared on Tuesday at Eleventh Mile in Cherthala, shortly after a bus and a car had passed through the newly opened overbridge. Residents had alleged that poor construction practices were responsible for the collapse. They initially opposed efforts to fill the crater, insisting that authorities first identify the cause of the collapse before carrying out repair work.

Residents also alleged that construction along the stretch was being carried out without adequate supervision by engineers. According to them, the retaining walls on sections with underpasses and overbridges were built using a single row of interlocking blocks. They claimed that soil had been washing away through the gaps between these blocks, weakening the road structure and increasing the risk of sinkholes, road subsidence and collapse. The incident has renewed concerns over the quality of construction on the National Highway project in the district.