Tunnel Boring Machine in Action

A crew of workers operates a boring machine for the construction of the Fréjus Rail Tunnel, also known as the Mont Cenis Tunnel. 

This machine, powered by compressed air, was designed to bore a series of holes into the rock. The crew required six hours to drill between 90 and 100 holes, each measuring 1.6 in (4 cm) in diameter and 31.5 in (80 cm) deep, except for a larger central hole, which remained empty. The smaller holes were then filled with powder and detonated in a synchronized manner, causing eight holes to explode simultaneously. This process resulted in an excavation approximately 27.5 in (70 cm) deep, 39 in wide, and averaging 15.7 in (40 cm) in height.

The original Fréjus Tunnel was 8 mi (12.8 km) long, connecting Modane, France, and Bardonecchia, Italy. Drilling began in August 1857, and the tunnel opened for traffic in September 1871.

The caption reads in the original French: Machine perforatrice en action au tunnel du mont Cenis.