What does enter the hole early, exit the hole late mean in a road tunnel?

"Early in the hole, late out of the hole" was first proposed by General Lu Zhengcao, the commander of the railway corps at that time (later General Lu became the Minister of Railways), which means that the tunnel should be long rather than short.

In tunnel construction, the surrounding rock of the tunnel entrance section is generally relatively broken and the geological conditions are poor, so the principle of minimizing the disturbance of the rock mass should be followed to improve the stability of the rock mass and the side and slope of the tunnel entrance section.

**Precautions for district selection line:

1) Trunk highways should try to avoid high-intensity areas, and when it is difficult to avoid, the route should be selected to pass at the narrowest place, and low embankments should be used.

2) When the route must pass through the high-intensity area, the favorable terrain should be used as much as possible to avoid cliffs, steep cliffs, complex terrain and unfavorable geological areas to reduce the damage that may be caused by the high-intensity area.

Appropriately extend the length of the cave and tunnel, try to avoid the large excavation of the mountain, advocate zero excavation of the hole, so that the vegetation around the tunnel mouth is properly protected, and maintain the original ecological landform, that is, "before the mountain is the first hole, try to stay away from the mountain before the hole". The construction of tunnels plays an important role in improving the technical state of highways, shortening the running distance, increasing transportation capacity, and reducing accidents.

Highway tunnel schematic design.

On the basis of the topographical, geological, meteorological, hydrological, social and natural environment of the area where the tunnel is located, as well as the relevant laws and regulations, the overall layout of the tunnel is comprehensively considered; Rough estimation of the amount of work to be constructed in the tunnel; Careful analysis of the safety of tunnel construction: adequate estimation of the use of the tunnel and long-term planning;

A comprehensive evaluation of the environmental impact is carried out to determine the economical, technically reasonable and profitable plan for the tunnel construction project. This process is called schematic design.

It means that when we are doing the tunnel, we must do concrete pouring or other forms of open hole structure at the entrance of the tunnel in advance before entering the tunnel to prevent the slag above the tunnel door from falling down and affecting the construction operation and life safety

If I guessed correctly, I would have described the length of the tunnel, and I could go in the morning and go to the other end in the evening. It's the same as a sentence describing the temperature difference, "Wear a cotton jacket in the morning and yarn in the evening, and eat watermelon with a stove."

In tunnel construction, the surrounding rock of the tunnel entrance section is generally broken and the geological conditions are poor, so the principle of minimizing the disturbance of the rock mass should be followed to improve the stability of the rock mass and the side and slope of the tunnel entrance section.

The design code and the construction code have made normative requirements for the location of the hole, emphasizing "early into the hole, late out of the hole", that is, appropriately extending the length of the hole and the tunnel, trying to avoid the large excavation of the mountain, and advocating zero excavation of the hole. The vegetation around the tunnel entrance is properly protected and the original ecological landform is maintained. The cave gate strives to be in harmony with the natural environment and cultural landscape.

Under the premise of maintaining the stability of the edge and slope, the hole should be implemented in time, and before entering the hole, combined with the actual situation of the hole, the anti-drainage measures on the surface of the hole should be made first.

In the case of large cross-section, shallow burial and poor geological conditions, pre-reinforcement measures such as surface pre-grouting and advanced long pipe shed grouting are usually adopted.