Water aquifer and loose soil above tunnel led to Telangana mishap?

Three days have passed since a portion of the under construction tunnel collapsed, trapping eight workers and rescue teams are racing against time to retrieve them.

Nagarkurnool: While water leaks are a common sight in tunnel excavations, what baffled the rescue teams and the staff working on the 44 km long Srisailam Left Bank Canal tunnel in Telangana, with whom DH interacted on Monday, was the continuous gush of water they encountered and loose soil raising concerns over the technical studies taken up before the project was commenced.

Three days have passed since a portion of the under construction tunnel collapsed on Saturday, trapping eight workers and rescue teams are racing against time to retrieve them.

“There has been continuous water oozing. For almost two kilometres, there was more than three feet of water. Even after draining out the water, the water is being accumulated. We are surprised with this phenomenon even though small water leaks were a common sight,” a civil contractor who had earlier worked on the SLBC tunnel told DH.

The civil contractor who lives close to the tunnel rushed to the site after the workers complained about the mishap on Saturday morning. Since then he has been at the tunnel site. Incidentally, though the team from The Robbin's Company saw a water leak, they didn't take it seriously.

According to the eyewitnesses, the workers joined the 6.45 am shift and around 8 am reached the 14km spot where the mishap happened at around 8 am.

As they started drilling, a loud explosion kind of mishap took place, and many ran from the spot, and eight close to the Tunnel Boring Machine (TBM) could not escape and were trapped.

World-renowned American company The Robbin's known for TBMs, along with Jaypee Associates, has been executing the SLBC tunnel work. While the work has been taken up from both ends, only 10 km of excavation remained. The water coupled with mud has been hindering the rescue teams from reaching the spot, which is 14 km inside the tunnel.

A geological fault line with a water aquifer above the tunnel surface where the mishap took place is suspected to have led to the soil loosening, and the workers on the 200-meter-long Tunnel Boring Machine (TBM) could not escape while others working on the site were able to escape.

After almost five years after the works were stalled Congress after  coming to power in 2023, tunnel works were relaunched just last week. The previous BRS government had stalled the project initiated by the then Congress government led by YS Rajasekhar Reddy as chief minister, citing some 'technical issues.'.

The tunnel has been planned to provide irrigation water to around four lakh acres and hundreds of villages under a gravity-fed irrigation system by drawing water from the Srisailam Project to the erstwhile combined districts of Mahbubnagar and Nalgonda. The tunnel passes through almost 400 m below the Amrabad Tiger Reserve in Nagarkurnool district.

Since the relaunch of works just four days before the mishap, around 12 meters of the excavation have been taken up.

Rat hole miners, Navy divers join rescue operations

Rat hole miners who were successful in helping the rescue teams in the Uttarkashi tunnel mishap in 2023, specialised navy divers, and a team from IIT Chennai with a mine detection robot, push cameras have joined the rescue efforts on Monday along with NDRF, SDRF, and Indian Army teams at the SLBC tunnel in Telangana's Nagarkurnool district.

Around six rat hole miners, known for their expertise in navigating confined spaces, arrived at the SLBC tunnel site from Delhi on Monday morning. Both the rat hole miners and the naval divers with whom DH had interacted expressed concern about the rescue operations due to the presence of thick mud and silt.

The conveyor belt that is used to transport the mined debris to the outside was also damaged. “Telangana government representatives had contacted us to help the rescue efforts here. As far as our understanding after the briefing from the authorities and also from the videos and pictures we have seen inside, there is a presence of water, which may hamper our efforts. However, we will try to do our job entrusted to us,” one of the rat hole miners, Qureshi, told DH.

The rat hole miners will go along with the NDRF teams into the tunnel to assess the situation and then devise their strategy. A group of naval divers from Eastern Naval Command (ENC) in Vizag had flown to the SLBC tunnel site. They arrived with advanced diving equipment. “There is silt and mud, what we have understood with the interactions with the rescue teams. We have to see how far we can navigate and reach the spot to rescue the trapped workers,” one of the Indian Navy divers told DH.

Chances of survival remote

As the days are passing, the chances of the trapped workers' survival have turned extremely remote. Members of the rescue teams, with whom DH interacted, expressed that there is no space available on the other side of the mishap spot, as it is the end of the tunnel where the excavation work had commenced just days before the mishap on Saturday.

The trapped individuals include two engineers, two operators, and four labourers from Uttar Pradesh, Jammu & Kashmir, Punjab, and Jharkhand. The intensity of the collapse of the upper surface was so intense that it had pushed the several hundred-tonne weighing tunnel boring machine almost 200 meters away, and the whole area is now filled with mud, water, and thick sludge.

“We were unable to reach the actual spot where the collapse had taken place as it's all filled with concrete debris, mud, and water. Though oxygen is being pumped, somehow we could smell carbon monoxide at the spot. The mud and silt, which was filled a few meters on Saturday morning, had gone up by several levels by Sunday night,” a member of NDRF battalion in Vijayawada deployed at the tunnel told DH.