Thirty-one men working in a massive underground tunnel in Los Angeles were rescued Wednesday night after a portion of the structure collapsed, officials said.

Workers were 400 feet (121 meters) underground and as much as 6 miles (9.6 kilometers) inside from the only entrance when the cave-in Wednesday evening threatened to trap them on the far side of the tunnel’s boring machine,

None of the 31 construction workers rescued in the tunnel sustained visible injuries, according to LAFD. Firefighters said construction workers climbed over a roughly 12 to 15-foot pile of dirt to escape.