The tunnel is a civil engineering structure and the product for the human breaking through the boundaries of the nat-ural environment, to improve the utilization of underground space and the traffic conditions. In 1970, the Organisation for Economic Co-operation and Development held a tunnel meeting that, after synthesizing the various factors, de-fined the tunnel as follows: "In some applications, under the ground in any way, shape and the size of cross-sectional area is larger than 2 square metres according to regulations".