The design principle of tunnel entrance is "early entry and late exit". Why?

Both the Code for Design of Highway Engineering and the Code for Construction of Highway Engineering issued by the Ministry of Communications require that the location of the tunnel entrance be standardized, emphasizing "entering the tunnel early and leaving the tunnel late", that is, extending the tunnel entrance and tunnel length appropriately, avoiding digging mountains as much as possible, and advocating zero excavation of the tunnel entrance, so that the vegetation around the tunnel entrance can be properly protected and the original ecological landscape can be maintained. The East Gate strives to be in harmony with the natural environment and human landscape. On the premise of maintaining slope stability, the hole should be constructed in time, and waterproof and drainage measures should be taken on the surface of the hole in combination with the actual situation before entering the hole. In the case of large section, shallow burial and poor geological conditions, pre-reinforcement measures such as surface pre-grouting and advanced long pipe shed grouting are usually adopted.

The key to getting out of the hole late in construction mentality is "late" Of course, here generally refers to the unilateral excavation of the tunnel. When the tunnel is about to be completed, the mood is exciting. In this case, it is easier to be careless, negligent and aggressive. Generally, landslides are prone to occur, causing unnecessary losses and accidents. Generally speaking, the reason why the accident rate of leaving the hole is higher than that of entering the hole is also here. Late, is to have patience, step by step, what should be done must be done, and what should not be done must be changed when the impact is seen. There is another link that must be grasped to stabilize the hole, that is, the personnel of the excavation class and support group must be supervised. This is the weak link and the place where the accident happened.