Tunnel vision: Experts divided on burrowing into Himalayas, worried about load-bearing capacity

Experts are divided on burrowing into seismically active Himalayas as they are worried about load-bearing capacity of the young mountains in the wake of the cave in at the under-construction Silkyara
Rescue and relief operation underway after a portion of an under-construction tunnel in Silkyara collapsed | PTI
Rescue and relief operation underway after a portion of an under-construction tunnel in Silkyara collapsed | PTI

DEHRADUN: Experts are divided on burrowing into seismically active Himalayas as they are worried about load-bearing capacity of the young mountains in the wake of the cave-in at the under-construction Silkyara tunnel

On the face of it, there was nothing amiss in the Char Dham Mahamarg Vikas Pariyojna in Uttarakhand that was inaugurated in the fag end of 2016. It aimed to enhance pilgrim connectivity to nine holiest of holy destinations, including Yamunotri, Gangotri, Badrinath and Kedarnath, by building all-weather roads in the Himalayas.

The project included a few tunnels so as to cut travel time and fuel cost in accident and landslide-prone areas. Negotiating hairpin bends on narrow ghat roads can be a pain in the best of times. Unfortunately, one of those tunnels in Silkyara is in big trouble as part of its roof caved in, trapping 41 labourers since Sunday last.

The most ambitious and controversial part of the project was the widening of 829 km of national highways 58, 94, 108, 109, and 125 by at least 10 metres, stretching and improving it into a two-lane carriageway with paved shoulders. It drew a firestorm of protests from locals and activists. When the matter went to the Supreme Court, the bench first capped the width of the highways at 5.5 ft. But after the government played the national security card citing Chinese threats—to press for ease of mobility of heavy defence equipment to the border—the court in December 2021 lifted the highway width ceiling.

While the government claimed it had completed various pre-project surveys, including hydrological, geological and geomorphologic investigations for the Char Dham project, other stakeholders kept hammering the point that the Himalayan region is seismically active and has experienced multiple disasters over the past 50 years. Several small and big earthquakes in the foothills of the Himalayas have been recorded. The Indian seismic map places the whole of Uttarakhand in zones IV and V. Zone V is seismically the most active region while zone II is the least. About 11% of the country falls in zone V, 18% in zone IV, 30% in zone III and the rest in zone II.

The recent accident at the under-construction Silkyara tunnel in Uttarkashi district has reignited the debate among geologists and scientists about the appropriate model of development for Uttarakhand's mountainous areas. The tunnel under construction by the National Highways and Infrastructure Development Corporation Ltd (NHIDCL) through Navayuga Engineering at a cost of Rs 853.79 crore aims to connect the Gangotri and Yamunotri axis under the Radi Pass area. When the project is complete, the tunnel will allow bidirectional travel, cut motoring time from 50 minutes to just 5 minutes and squeeze the present Silkyara to Dandalgaon distance of 25.6 km—through steep hilly and narrow roads that are prone to accidents and landslides—to just 4.5 km. Had the existing road been widened, the rich flora and fauna of the Radi Top mountains with a dense cover of rhododendron vegetation would have been completely destroyed.

Tech-wise doable

Prof Satyendra Mittal, a civil engineer at IIT-Roorkee, who has expertise in geotechnical and earthquake engineering, told this newspaper, "The mountains of Uttarakhand are fragile. They are also called young mountains. Tunnels can be built in such mountains, but with utmost caution." On the question of suitability of tunnel technology, given the strength of rocks in the hilly areas of Uttarakhand, Prof Mittal says, "Tunnels should be properly lined with strong waller beams and concrete or steel liners."

In many countries, nailing of soil mass is also being used to strengthen tunnels, he adds. "In Japan, where earthquakes occur almost every day, there are many tunnels, which perform satisfactorily. The design of the tunnel should be made tolerable to earthquake loads and seismic vibrations, corresponding to zones IV and V." The Centre, he goes on to suggest, ought to create an oversight authority like, say, the Director General of Tunnel Safety, on the lines of the Director General of Mines Safety.

Prof Manish Shikhande, head of the department of earthquake engineering at IIT-Roorkee, is in two minds about the tunnel construction in seismic mountainous regions. Quoting Gautam Buddha, he says, "Take the middle path, extremes are always bad." While no development is a bad sign, so is extreme development, he philosophically observes. "In my opinion, tunnels are the most sustainable and economical way of connectivity. Tunneling is not a novelty but an age-old construction technique," he points out, adding, "tunnels are constructed all over the world, including in Japan and Korea, which are seismically highly active areas." The only difference is that the rock strength is higher in the Japanese hills. Tunnelling is decidedly a better way of connectivity than cutting mountains to build roads.

"Any engineering facility can be designed to withstand earthquakes, though mountain formations in the Garhwal Himalayas are mainly sedimentary rocks, which are weak formations," says Prof Shikhande.

"Before constructing a large number of tunnels, it is important to ensure that the project is taken up after studying the geological changes in the vicinity and its far-reaching consequences," explains environmentalist Om Prakash Bhatt.

Train burrows

Experts believe the continuous vibrations during train movement is another issue related to tunnels that could keep the Uttarakhand hill slopes unstable forever. Jai Singh Rawat, author and historian on Himalayan issues, is of the opinion that "building tunnels is not good for the health of the Himalayas as it hollows it out."

It is a well-known fact that the Tapovan Vishnuprayag tunnel was responsible for the sinking of Joshimath town in Chamoli district of Uttarakhand. "Besides, houses in Dhari and Sukhi villages along the Rishikesh-Karnaprayag rail project, have developed cracks, 86% of which is due to tunneling. Some village houses in Rudraprayag, too, have cracks," says Rawat.

Dev Raghvendra, an environmentalist who has been quite vocal on issues related to the threat posed by helicopters carrying pilgrims during the Char Dham Yatra season, says: "When the sound of a helicopter flying can adversely affect the homes and ecology of a region, the roar and vibration of moving trains along tunnels on the rail line to Karnaprayag would decidedly have an
adverse effect on the environment and vegetation here." The spurt in anthropogenic activities, mainly the felling of trees, has made the hill slopes extremely unstable.

This is the reason why there has been an increase in the number of landslides in the Himalayas, which has been aggravated by heavy rains and cloudburst events due to climate change, Raghvendra reasons. "Excavating a tunnel induces stress changes. The consequent deformation within rock formations could also contribute to landslide vulnerability," he adds. Controlled use of explosives to cut through rock formations in order to construct tunnels often weakens the mountains, causing landslides, besides generating huge amounts of excavated rock waste, Raghavendra points out, adding that "irreversible effects on groundwater, such as declining water levels, have also been observed in tunnel construction areas." Unlike many mountain ranges in the world, the Himalayas are the youngest and most active in terms of tectonics (the science behind earthquakes). There is a perception that the construction of tunnels can reduce the infrastructural impact on the environment.

"But these subsurface structures can cause enormous damage to the environment, including the concentration of pollutants from mixed traffic exhausts by the microenvironment without sunlight and limited dispersion in long-distance tunnels," opines another environmentalist on the condition of anonymity.

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