Fears over stability of hills above tunnel prompt call to pause rescue ops
Hyderabad: In a huge setback to the rescue operations at the collapsed SLBC tunnel in Nagarkurnool district, a decision is learnt to have been arrived to suspend rescue attempts until the stability of the hills above was established, especially at the 13.9-km point where the collapse had occurred on Saturday.
Also contributing to the decision was the finding that the levels of water and slush were rising significantly inside the tunnel. The assessment of the conditions inside the tunnel was made after teams of the NDRF, SDRF, Army, and Marcos (Marine Commando) divers from the Navy ventured inside at about 3 am on Monday.
Another team that entered the tunnel at 3 pm on Monday and returned around 9 pm, reported heavy water ingress.
Sources involved in high-level discussions at the site on Monday told Deccan Chronicle that scientists from the Geological Survey of India and the National Geophysical Research Institute were deployed to the site to assess the conditions and stability.
“The consensus that was arrived at was that the conditions in the tunnel were unstable, and there may be a possibility of further collapses. However remote this possibility maybe, since this poses a significant risk to anyone entering the tunnel, it was decided that the best course of action is to let the GSI and NGRI scientists study the conditions. Only when they give the go-ahead should any further rescue attempts be mounted,” the source said.
Also roped in was the Hyderabad-based National Remote Sensing Centre for satellite data of the Nallamala hills above the tunnel collapse zone. The NRSC scientists were to compare the latest pictures with previous imagery to see if there had been any topographical changes – differences in the surface levels before and after the collapse – that might indicate serious geological changes occurring over the tunnel’s alignment.
It was suspected that the collapse of the tunnel could have resulted in a void forming over the zone which in turn may have a bearing on the column of rocks that comprises the hills above.
The stability and safety of the tunnel was at the centre of the discussions on Monday between state government officials, the GSI and NGRI scientists and representatives of Jaiprakash Industries, the company building the tunnel, and senior NDRF, SDRF, Army officials, it is learnt.
Also at the site was Christopher Cooper, a tunnelling expert with L&T who has been heading the company's tunnel boring machine (TBM) operations for 40 years.
Everyone agreed that it was important to first understand the stability issues and only then take a call as to when the next rescue operation can begin, the sources said.
With regard to the assessment of conditions inside the tunnel, where the collapse occurred at about 8. 30 am on Saturday, a source told Deccan Chronicle: “When the first team went in around 3 am, on Sunday, it found that there was some five metres of soil and rock slush at the visible tail end of the TBM. The team that went in just after Sunday midnight, found that just in 24 hours, around 3 am, on Monday, the slush rose to 7 metres indicating continuing pouring in of soil, and possibly rocks into the tunnel from the collapsed section. The water level too was rising and pushing towards the tunnel mouth as is the slush.”
“This can mean two things. One, the section where the collapse occurred may have become larger, letting in more soil, rocks and water into the tunnel, or that another ‘geological event’ – a euphemism for a fresh breach in the tunnel – may have occurred. Since this may be the case, it is best that prudence and caution be the choice for the time being,” the official explained.
Meanwhile, a combined rescue team that went into the tunnel at around 3 pm on Monday, returned around 9 pm, and it is learnt that it reported heavy water ‘ingress’. The team managed to use the locomotive trolley used by the workers normally used to reach the TBM, but managed to make it just over 11 km on the tracks, and had to make their way for 1 km walking on the conveyor belt system mounted on the side of the tunnel.
“The last 200 metres of going forward was through the ventilation duct,” a source said, indicating the worsening conditions on the tunnel floor, as well as possibly in the roof section of the collapsed portion of the tunnel.
Incidentally, earlier it was claimed that GSI experts had visited the tunnel site two months ago and gave the go-ahead for resumption of operations that started on February 17. However, sources confirmed that no official team from the GSI had visited the site in the recent past and if anyone had done so, it was possibly retired GSI scientists who were privately engaged by the contractor.
The sources were emphatic that GSI had not sent anyone officially until Monday, the day when two of its scientists were deployed to the site to assess the conditions.
