Open-air extension to road or railway tunnel through mountain for protection against avalanche is constructed using lost shuttering and metal frames erected on floor plate

摘要

The tunnel is constructed by first laying a concrete slab (6) on flattened and prepared ground. Heavy rails are laid along the slab to carry a support frame for a longitudinally movable inner shuttering (14). Metal reinforcement bars and a lost outer shuttering (12) are arranged on the outside of the movable shuttering. The lost shuttering is open at the top.