Nepal is surrounded by rugged mountains. Chronic traffic congestion and accidents had become major challenges on the roads connecting the capital, Kathmandu, with other major cities. To address this situation, the “Nagdunga Tunnel” (total length: approximately 2.7 kilometers)—Nepal’s first tunnel equipped with modern facilities—was constructed with cooperation from JICA and other organizations. It took about seven years to complete the project, which was finished in July 2026. Behind the scenes of this long-awaited tunnel project lay the challenges and collaboration between Japanese and Nepalese engineers.
Scenes from the Tunnel Construction
“World-Class Infrastructure” Comes to Nepal
The completion ceremony held at the end of July was attended by the Minister of the Ministry of Infrastructure Development of the Government of Nepal, the Japanese Ambassador to Nepal, and the President of JICA, among others. Mr. Saujanya Nepal of the Nepalese Ministry of Roads, who served as the project manager for the Nagdunga Tunnel construction project, recalled the occasion, saying, “It was a moment of pride for both Japan and Nepal and an event that symbolized the cooperative relationship between the two countries.”
Completion Ceremony for the Nagdunga Tunnel
The project has received extensive coverage in local media, and citizens have welcomed it, saying, “Nepal now has world-class infrastructure of the kind I’ve only ever seen in developed countries.” Mr. Nepal expressed his hopes, stating, “The completion of the Nagdunga Tunnel will be a turning point in the development of our country’s infrastructure toward a more modern standard.”
The completed Nagdunga Tunnel (Courtesy of Ando Hazama)
The long-awaited tunnel project was driven by challenges in the transportation system. In recent years, as Nepal’s economy has grown, logistics and passenger traffic have expanded, but the development of the road network has failed to keep pace, leading to chronic traffic congestion. Furthermore, during the rainy season, accidents caused by landslides have occurred, making traffic safety a major concern.
To address this situation, JICA conducted a survey of traffic volume and geological conditions at the planned site for the Nagdunga Tunnel. As a result, it was determined that constructing the tunnel would be an effective measure for reducing traffic congestion and the risk of accidents in this area. Furthermore, after comparing and evaluating geological stability as well as environmental and social impacts, an optimal route through more stable bedrock was identified. The construction of the Nagdunga Tunnel proceeded through a process of repeated preparation and careful consideration.
Traveling this stretch used to take between 30 minutes and an hour by car, but with the opening of the tunnel, the travel time has been reduced to 6 to 7 minutes. In addition to ventilation and lighting systems, the tunnel is equipped with emergency escape shafts for use in case of an emergency, and it is expected to serve as a new model for Nepal’s road infrastructure.
In early September, shortly after the tunnel opened, an incident occurred that demonstrated its effectiveness. A section of the existing road leading to Kathmandu collapsed, causing serious traffic disruptions. At that time, emergency vehicles, such as ambulances, used the tunnel to reach the scene. The tunnel thus served not only to alleviate everyday traffic congestion but also as an “alternative route” that remained passable even when the main road was obstructed.
Until now, cars had to cross the Nagdunga Pass, which features a series of sharp curves, but with the opening of the tunnel, it is now possible to take a shortcut around the mountain pass, reducing the travel time from 30 minutes to an hour to just 6 to 7 minutes.
The Struggle Against Challenging Ground Conditions
Although we made thorough preparations based on extensive research, the tunnel construction turned out to be more difficult than anticipated.
Kenichi Inoue, who served as site manager for the major construction firm Ando Hazama—the company responsible for the project—reflects, “While digging the tunnel, I truly came to appreciate the unique challenges of the Himalayas and the awe-inspiring power of nature.”
Nepal is home to the Himalayan mountain range, which features a series of 8,000-meter-class peaks, including Mount Everest, the world’s highest mountain. The Himalayas were formed by the collision of the Indian Plate and the Eurasian Plate, and tectonic activity continues to this day. As a result, ground pressure in the mountainous regions is extremely high, and there are many areas where the bedrock is fragile and prone to collapse. These harsh geological conditions posed a major challenge for tunnel construction.
At the Nagdunga Tunnel as well, we faced numerous challenges, such as rock being pushed out into the tunnel due to strong ground pressure and sections of rock collapsing. Nearly 40 rockfalls occurred during the construction period.
“We experienced continuous deformation and ground movement that would be unthinkable in a typical tunnel construction project,” says Mr. Inoue.
In tunnel construction in Japan, deformation caused by ground pressure is generally limited to a few centimeters. However, at this site, deformation reached a maximum of approximately 1.5 meters. Forces strong enough to snap the steel beams supporting the tunnel interior were exerted, forcing the engineers to respond to ground pressure that exceeded their expectations.
Inside the tunnel where the cave-in occurred (courtesy of Ando Hazama)
Challenging Construction Projects Supported by Measurement
Surveillance played a crucial role in these challenging ground conditions. In tunnel construction, the behavior of the surrounding ground after excavation is continuously monitored.
Mr. Inoue repeatedly explained the importance of precise measurements to the local workers in Nepal. Why did they have to take measurements from the exact same spot? Why was such high precision required? As the entire site team came to share this understanding, the construction work proceeded.
In typical tunnel construction, measurements are taken at intervals of 20 to 30 meters. However, due to the challenging geological conditions at this site, measurements were required at 10-meter intervals. Furthermore, because the ground was constantly shifting, it was necessary to conduct measurements covering a wide area of approximately 200 meters every day. Even during periods when excavation was suspended, the on-site workers continued to take measurements, diligently recording the ground’s movements and changes.
Mr. Inoue reflects on that time as follows.
“The people of Nepal never cut corners, even on labor-intensive tasks, and worked with true perseverance. Without that data, I think it would have been difficult to understand why the ground was shifting in this tunnel.”
Breakthrough Ceremony for the Nagdunga Tunnel (Courtesy of Ando Hazama)
Experiences That Shape the Future
Mr. Inoue believes that the skills and experience gained through this project will be an asset to both Nepal and Japan.
While Japan continues to face a labor shortage in the construction industry, Nepal is home to many young people who are eager to “learn Japanese construction techniques.” “I hope that this new connection will serve as a starting point for people from Nepal to gain experience and knowledge in Japan, and then return to Nepal to make a difference,” says Mr. Inoue.
Mr. Nepal said, “This was a valuable opportunity for Nepalese engineers to learn about modern road tunnel construction firsthand on-site. I hope this will lead to the construction of many more tunnels in Nepal in the future and that our cooperation with Japan will continue.”
Mr. Inoue also expressed his hopes, saying, “We’ve received many comments from people saying that working alongside Japanese companies has helped them acquire technical skills, knowledge, and the ability to tackle challenges. I hope we can see a flow of talent—people who work in Japan to deepen their experience and expertise, and then return to Nepal.”
This single tunnel, which took seven years to complete, bears witness to the collaboration between Japanese and Nepalese engineers as they overcame numerous challenges.
© Source JICA