How is the Zojila Tunnel that will link J&K with Ladakh being built at 11,500 feet?

The 13.15 km long Zojila Tunnel that will link Jammu and Kashmir with Ladakh at 11,500 feet is being built by around 1,200 engineers, mechanics, technicians and labourers. They are working simultaneously from both ends despite snowstorms, sub-zero temperatures, high-altitude sickness risks and avalanche threats. The tunnel has been excavated using the New Austrian Tunnelling Method (NATM).