What are the key points for earthwork excavation at the tunnel entrance?

The following are the key points of earthwork excavation at the tunnel entrance brought by Zhongda Consulting for your reference.

1. The earthwork construction at the entrance of the cave should be avoided during the rainy season. If construction is really necessary during the rainy season, a strict construction plan and protective measures should be formulated. At the same time, monitoring and inspection of the stability of the hillside should be strengthened. For the earthwork at the end wall of the cave entrance, the construction timing and construction method should be selected based on the stability of the stratum, the construction season of the cave entrance and the tunnel construction method.

2. The excavation of earthwork on the side slopes and upward slopes of the cave entrance should reduce the disturbance to the rock and soil, and large blasting is strictly prohibited. Topsoil and shrubs that may collapse on side slopes and upward slopes, as well as pumice and dangerous stones on side slopes and upward slopes must be removed or reinforced, and uneven slopes must be smoothed.

3. Before entering the cave, the surface and slope should be reinforced and protected according to the design requirements. When excavating edges and slopes in soft strata, it is advisable to provide support along with the excavation, and monitor and check the stability of the hillside at any time. When landslides or collapses may occur at the entrance of the cave, preventive and stabilizing measures should be taken promptly to stabilize the slope and ensure construction safety. Auxiliary engineering measures such as surface mortar anchors and surface grouting can be taken, or measures can be taken to stabilize the slope during roadbed construction.

4. For the construction of biased openings, support, back-pressure and backfilling should be done before excavation. The excavation method should be selected based on the biased terrain conditions, and the biased voltage must not be aggravated by human factors.

5. The tunnel entrance slope and incline shall be constructed using the open-cut method, and the excavation shall be carried out in stages and in layers from top to bottom. In the first stage, the tunnel is excavated to the designed temporary cave surface, and steps to enter the cave are reserved based on the surrounding rock conditions and the method of dark cave excavation. In the second stage, the remaining portion is excavated to form a permanent side slope. Excavation at the bottom or overlapping top and bottom excavation is not allowed. When there are adjacent buildings (structures) at the entrance of the cave, microseismic controlled blasting should be used.

6. The slope drainage system at the entrance of the cave should be completed before the rainy season. Tunnel drainage should be reasonably connected to the drainage system outside the tunnel. It should not erode or soften the foundation of the tunnel and open tunnel, and should not wash away facilities such as the roadbed slope in front of the tunnel entrance and the cone slope of bridges and culverts.

7. The permanent protection project at the entrance should be completed as soon as possible following the excavation of earth and stone. The bearing capacity of the foundation should meet the design requirements.

8. Construction pools are prohibited within the cave body above the slope of the cave entrance.

9. The earth and stone that should be excavated should be completed before entering the cave. The discarded earth and stone should be piled at the designated location. No spoil or stone should be piled on side slopes or inclines.

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