Repeated disasters put tunnel solutions at center of highway planning

Repeated floods and landslides have damaged the Krishna Bhir section of the Prithvi Highway, prompting the government to explore a tunnel or viaduct as a safer long-term alternative

Nagdhunga Tunnel. File photo

KATHMANDU: The government has put forward the option of constructing a tunnel or a viaduct to reduce the risk of landslide and river erosion in Krishna Bhir. After the technology adopted earlier for landslide prevention of this section of the Prithvi Highway, which connects Kathmandu with other cities, was completely damaged by the flash flood on August 26 and the monsoonal flood on August 30, the government has started searching for alternative solutions.

Currently, the civil engineering and bioengineering technology used since 2004 by the Department of Roads under the Ministry of Infrastructure Development has kept the slope stable for about a decade. According to a study regarding the Krishna Bhir landslide published in JournalsPub in 2016, after 2014, the lower part of the cliff was eroded, and rocks began to appear, showing that it was at high risk of erosion during monsoonal rainfall.

When the August flood increased the erosion of the Trishuli River, about 100 meters of road in the Krishna Bhir area was completely damaged, shutting down road traffic for about 21 days. For the immediate term, the road was brought into operation by opening a new track slightly above where the landslide occurred. Although traffic came into operation from September 17, following continuous rain, a large landslide with a huge boulder fell again on September 24, blocking it. After clearing the landslide, the Krishna Bhir section came back into operation on September 29.

The roadway connecting Kathmandu with China’s nearest trade and tourist pass at Rasuwagadhi lies in debris.

The government had already started searching for alternatives as soon as the landslide closed the road. According to the information given by Director General Bijaya Jaishi of the Department of Roads at the meeting of the Infrastructure Development Committee of the House of Representatives on September 21, technical studies have been forwarded on the options of whether to construct a tunnel or connect the road by building a viaduct in front for a long-term solution for Krishna Bhir. Director General Jaishi of the Department of Roads stated that the technical study has already started, and after the report is prepared within about two months, there is a plan to go into the tender process for construction. “After the technical report arrives, there is preparation to go into the tender process for construction,” he says.

On August 26, after a glacier along with rocks fell from the northern slope of Langtang Lirung, the resulting flash flood damaged 69 km of roads and 37 motorable bridges along the Bhote Koshi and Trishuli River corridors. The road route connecting Rasuwagadhi, the nearest commercial and tourist border point with China for Kathmandu, has turned into rubble. Meanwhile, voices have started raising to give priority to the construction of the proposed Tokha-Chhahare tunnel connecting the border of China and Rasuwagadhi.

According to Geologist Ranjan Kumar Dahal, a tunnel on a road route is a technology of taking a road by making a hole inside the ground, and a viaduct is a technology of taking a road by making a bridge-like structure on top of multiple pillars to bypass a landslide. He says that both these technologies can bypass risky disaster sites of floods and landslides on the Prithvi Highway, just like at Krishna Bhir. “In Krishna Bhir, it was attempted to be stopped through simple and cheap bioengineering technology; if the large flood had not come, it would probably have sustained longer,” he says.

Installing tunnels or viaducts ranging from 50 to 800 meters in key areas would help bypass flood and landslide risks and cut down distances on the Prithvi Highway.

The method of using grass, shrubs, and other vegetation along with local materials to stabilize slopes and reduce surface erosion and soil erosion is called bio-engineering technology. He adds, “Since rocks have started appearing after the recent landslide, technology that increases strength in it can be used, and for the long term, a tunnel or viaduct can be installed.”

According to his statement, by constructing tunnels or viaducts of 50 to 800 meters in various places, risks of floods and landslides on the Prithvi Highway can be bypassed and distances can be reduced. He says, “With a 700-meter tunnel or viaduct, a 3 km road bend can be shortened.”

Subterranean solutions for highways

Just as Geologist Dahal said, with the objective of straightening and shortening roads with many bends and steep inclines, reducing traffic pressure, bypassing active landslides, and making travel easy, a tunnel was built from the Nagdhunga of Kathmandu to the Sisnekhola of the Dhading road section. The government brought the Nagdhunga road tunnel near Kathmandu into operation this year. This tunnel has shortened the travel distance of the Nagdhunga-Sisnekhola section. A road that takes about half an hour to reach Nagdhunga from Sisnekhola after navigating around 19 bends and hairpin bends can be crossed in about seven minutes through the tunnel.

Nagdhunga Tunnel. File photo

After about 80 months from the start of construction, the tunnel, which came into operation with an official inauguration on July 27 this year, was constructed with a concessional loan of about JPY 21.2 billion from the Government of Japan and an investment of Rs 6 billion from the Government of Nepal. Construction started on November 13, 2019, after then-Prime Minister KP Sharma Oli laid the foundation stone at Tutipakha, located in Chandragiri Municipality-2, in late 2019. Then Prime Minister Pushpa Kamal Dahal, ‘Prachanda,’ did the breakthrough of the main tunnel of the tunnelway on April 15, 2024.