China has a vast stretch of territory, of which mountains and heavy hills account for about 75%. Tunnels are inevitably required to be constructed to allow roads to cross mountainous or hilly areas. The tunnel is a basic form for utilizing the underground space, and is an important component for forming transportation networks, such as railways, highways and urban subways. China has made a remarkable achievement based on the mature drilling techniques such as the drill-blasting method, drilling with tunnel boring machines and shield tunneling method, etc., tunnel construction and support technique adapted to geological conditions and modern operation and management modes. Nowadays, China has the rapidest development speed, the largest number and the most complicated construction conditions in tunnels and underground engineering. However, the accumulation and mastery of key techniques of tunnel constructions in China are still in the primary stage, and resolutions for accidents, such as collapses, water inrush and burst, hole shrinkage and support cracking are under-developed, which seriously threatens the safety of front-line construction workers and even causes severe casualties and property loses. The delayed blocking collapse of the tunnel is the most dangerous accident among those construction accidents threatening the safety of construction workers. During such tunnel accident, the construction workers cannot escape from dangerous areas in time, which leads to severe casualties.
The conventional method for solving the delayed blocking collapse is to place escape pipes on the bottom of tunnel sidewall. In principle, such escape pipe may help those front-line construction workers to escape from accidents, but connection of round pipes are not convenient, and multiple round pipes are connected via sleeve pipes, so connecting portions are easy to be broken. According to long-term construction site investigation, due to the disadvantages of too much interfaces, unsealing and inconvenient storage and transportation, the round pipes used at the construction site are often found to be placed outside the tunnel. When the blocking collapse happens in tunnels, the escape pipes are a hidden threat for the safety of the construction workers, because the outside escape pipes which cannot be used for the emergency escape may even hamper on-site rescues. Therefore, when tunnels are subjected to an accident, such tunnel escape pipes have a certain impact on the escape of the construction workers inside the tunnel and the rescue of the rescue workers outside the tunnel.
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