Probe drill exercise can check tunnel collapse accidents, says expert

The Silkyara tunnel collapse in Uttarakhand in November 2023 and the recent Srisailam Left Bank Canal (SLBC) tunnel collapse in Telangana underline the importance of a thorough probe drill to check such incidents, N.R. Acharyulu, former Director of Hindustan Construction Company and a tunnel expert, has said.

The Silkyara tunnel collapse in Uttarakhand in November 2023 and the recent Srisailam Left Bank Canal (SLBC) tunnel collapse in Telangana underline the importance of a thorough probe drill to check such incidents, N.R. Acharyulu, former Director of Hindustan Construction Company and a tunnel expert, has said.

A spark neglected burns the house, goes the adage. “A 2-inch probe drill, before boring a 9-diameter tunnel, would give ample signals to avert an impending disaster. As an engineer, I can say that probe drilling will certainly reveal various aspects of geological strata and the treatment required to support the exposed weak rock, lagging over the ribs and packing with backfill concrete,” Mr. Acharyulu told The Hindu on Wednesday.

It’s an established fact that a majority of tunnel collapses occur due to human negligence like faulty DPR and non-adherence to the stipulated methodology during execution, the tunnel expert said.

“Failure to deploy the right method for the rock encountered, ignoring the crucial step of probe drilling dismissing it as a ‘laborious and time-consuming activity’ in the eagerness to accelerate the progress of tunnel boring, negligence in maintaining the log on geological data during the progression of the tunnel, failure of geologists and tunnel in-charge in planning and executing the work based on log and geological data are among the reasons for tunnel collapses,” says Mr. Acharyulu, who has executed several tunnel projects across India.

The other reasons are dereliction of responsibility by tunnel engineers in insisting on tunnel-execution based on log data on geological strata, absence of technical audit in rock classification assessment methodology deployed, and diluting the total quality assurance.

“Tunnel collapse brings the work to a halt for months, resulting in time and cost overruns and possible loss of lives. Certain accidents may require realigning of tunnel, another cost-intensive and time-taking exercise. It is estimated that an underground project costs over two to five times higher than the on-ground project of similar nature, against which the cost of invoking discipline is negligible,” he said.

Mr. Acharyulu highlighted the dire need for strict compliance with codes and safety norms. The project team needs to be motivated with lucrative incentives upon completing the project free from accident.