‘If you are constructing the tunnel in the Himalayan region, then if you have constructed 10 metres of tunnel, first you will have to do proper treatment and ensure the stability of this constructed structure.’
‘You cannot just throw concrete on the ceiling and sidewall of the tunnel for permanent stability. That will not work.’
Dr Yaspal Sundriyal, professor of Geology at the Hemwati Nandan Bahuguna Garhwal University, explains to Prasanna D Zore/Rediff.com the probable reason behind the tunnel collapse at Silkyara and the challenges that the rescuers could face in their effort to extract the 41 workers who have been trapped inside the tunnel since November 12.
What is your assessment of the rescue efforts being taken in getting the 41 workers trapped inside the Silkyara tunnel?
The measures adopted by all the technical experts till now have failed to show any success. Machines and other technical tools are being brought from outside the country as well as from Indore but still the situation has not changed much.
The mountain (through which the tunnel is being dug out) at Silkyara tunnel contains phyllite (mostly contains clay and micaceous minerals), a very weak rock.
Earlier when drilling machines were used, the non-technical people told that the mountain is made of large rocks containing talcum powder. Actually, it is not talcum powder, but phyllite rocks which contain micaceous substances. So the lithology or the rock type is very weak.
When they started constructing the tunnel, they started constructing it from both sides — from the Silkyara and from Dandalgaon; Silkyara end is in the Bhagirathi Valley and Dandalgaon is in the Barkot area.
Construction of this 4.5 km long tunnel would have likely eased 20 to 25 km of tough road conditions making it easier for Char Dham passengers. Given the geology of the area, it was difficult for them to widen the existing roads so they started constructing tunnels.
We appreciate this effort, but at the same time the Himalayas are very sensitive mountain ranges; they are still uplifting.
Given that the entire Himalayas is hazardous — and any infrastructure project like construction of tunnels, road widening, construction of the hydro projects — you will have to take extra care.
One fails to understand why the construction company did not use tunnel-boring machines or TBMs. That is a very unfortunate part.
If they did not use TBMs, it means they used dynamite to make way for the tunnel and through JCBs they are digging the hill to construct the tunnel. The many tunnels where they have finished the construction work, they have not used the TBMs.
It is for the government and the construction company to answer why they are not using TBMs.
What are the advantages of using TBMs?
The TBM machine is just a boring machine, but it is safer because it disturbs a limited portion of the area where the tunnel is under construction while uncontrolled blasting and diging process using a JCB machine disturbs unlimited area of the surface where the tunnel is being constructed.
As a geologist, would you believe that the construction company should have used TBMs?
They should have used tunnel-boring machines.
The other critical factor is that to provide stability to those parts where tunnel work was almost completed, they used high-pressure machines to throw the concrete on the ceiling and sidewalls of the tunnel to hold the loose material from falling.
While this technique gives some stability to the ceiling and side walls that stability is not enough to bear the load of the entire hill.
They have done RCC (reinforced concrete cement) treatment only up to 200 metres from the Silkyara side. And the tunnel collapsed after 250 metres (from the Silkyara side).
Earlier it was said that the tunnel collapsed only about 55 metres (from the mouth of tunnel) then they (the government officials) said 60 metres because they don’t have any exact measurements.
The other concern is that there could be even some giant boulders (between the mouth of the tunnel and the place where the 41 workers are still trapped). And if you think that we will drill and bore and penetrate through the debris that has fallen and damaged the tunnel, then certainly in some areas, these machines will also encounter big boulders, drilling through which will be very difficult.
These big boulders could be another huge challenge hindering the rescue efforts.
The other unfortunate part is there was no emergency exit built inside the tunnel which could have allowed the workers a safe passage in case of such eventuality.
Why was an emergency exit route not available inside the Silkyara tunnel?
Actually, they (the 41 workers) were working inside the tunnel when it collapsed. The construction company should have done proper lining — lining is a technical word which means use of iron pipes in the arch shape or horseshoe shape to give proper stability to the tunnel. But they have not done that. They thought they will do that later on.
Any tunnel which is under construction or constructed the provision of emergency exit is the part of design, but in the Silkyara tunnel no emergency exit was constructed.
Is the rock composition of the mountains in this belt stable enough to go for digging tunnels?
The engineering properties of the rock and soil in the Himalayan region are not suitable for this kind of tunneling because we do not have continuous rock surfaces. The rocks found in this region are phyllitic rocks made of clay minerals.
Some people are saying some underground water was also trickling in the tunnel. When these clay minerals come into contact with the moisture, the process of pinching and swelling occurs. This swelling-pinching makes the rock weaker and weaker.
If you are constructing the tunnel in the Himalayan region, then if you have constructed 10 metres of tunnel, first you will have to do proper treatment and ensure the stability of this constructed structure.
You cannot just throw concrete on the ceiling and sidewall of the tunnel for permanent stability. That will not work.
Given that the experts working on the safety and rescue of these trapped workers are planning to drill from the top as well as horizontally from two more sides. Do you think it will bear any success?
It is not easy to judge right now because earlier also they have penetrated one drilling machine and that failed. And again they called another machine from Indore that also failed. Now I heard that they are doing geophysical survey.
If you are constructing such type of infrastructure in the Himalayan region, then all geological survey, geophysical surveys should be done before you implement the project. What is the use of the geophysical survey now? I cannot understand.
During the geophysical survey, if you will run the ground penetrating radar, it will give you the inner picture which will not be more than 20 or 25 metres of high resolution.
That will actually not give any results.
What more measures could the rescuers take to reach the workers who are trapped?
They will have to make another tunnel. Actually, in any tunnel construction some exits are also constructed, which they (the construction company Navayuga Engineering) have not done. Each such edit has one exit and tunnels are open from both sides.
This is the difference. These exits are constructed as emergency exits. Had they constructed these exits at every one kilometre then the solution would have been different. But they have not done any such type of work in the tunnel. 41 lives are at stake since 10 days.
If they will drill from the upper side vertically, then during the vertical drilling, the ceiling of the tunnel will get damaged. There is a possibility that more such parts of the tunnel may fall down.
But if they plan to construct two more 300 metre tunnels horizontal to the existing tunnel where these workers are trapped then maybe they can bore one exit or small tunnel between these two tunnels, and that may be one of the way out. But the construction of those parallel tunnels should be strictly by the tunnel-boring machines.
Not by dynamite. They can’t dynamite the mountain.
After this mishap, do you think the government as well as construction companies will be more cautious while digging tunnels in this part of the Himalayas?
First of all, the government will have to audit and evaluate the strength of the tunnels and railway tracks which are being constructed in Uttarakhand. About 60 kilometres of tunnels is proposed to construct the railway track and three or four tunnels are completed.
I don’t have any reason to believe that the government will take any lesson from this incident because despite the 2013 Kedarnath flash floods in this region, people have continued to construct their houses near the riverbed or near areas which were declared unsafe.
Unless the government frames foolproof rules on how to construct houses near riverbeds or how to use the highly sensitive Himalayan landforms to build railway tracks and construct tunnels and roads, nothing can be done.
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