An ill-starred effort to bore one of the deepest tunnels in the world has restarted in the mountains of northern Peru after months of delays due to rock bursts. The $247-million Los Olmos irrigation project was halted when the tunnel-boring machine at work on the 12.5-mile-long tunnel (with 6,890 ft of overburden) was damaged by rock bursts in April. On July 8, engineers with Brazilian construction firm Odebrecht were able to restart the TBM, but rock bursts continue to hinder progress. In August, work began on the tunnel’s opposite approach using conventional drill-and-blast methods. The tunnel breakthrough is now slated
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.