Preparation work has been completed for a project to remove a towering rock over the Kitanomaki Tunnel on the Joshin-Etsu Expressway in Annaka, Gunma Prefecture. (Kazuki Masuda)

ANNAKA, Gunma Prefecture--Work will start here in May to remove a towering fortress-like rock face that poses a threat to the Kitanomaki Tunnel below, East Nippon Expressway Co. said.

The rockslide hazard stands about 70 meters tall over the entrance of the Kitanomaki Tunnel located between the Matsuida-Myogi Interchange and the Usui-Karuizawa Interchange on the Joshin-Etsu Expressway.

The entrance to the 190-meter-long tunnel, which opened in 1993, is on the Nagano Prefecture side.

The rock face got its fortress look through the layers of scaffolding set up for drilling work in the rock-removal project.

A fatal rockslide at a tunnel in Hokkaido in 1996 led to safety inspections of tunnels nationwide. A rockfall risk was confirmed at Kitanomaki Tunnel.

A policy to remove the rock face was decided in 2014, and preparation work began in 2017.

From May, chunks of the rock will be carried out from the backside of the tunnel after the drilling work.

The project is expected to remove around 95,000 cubic meters of rock over five years.

The area is precipitous. Special roads and an elevator that can load two large trucks have been built for the rock-removal work.