1. The tunnel shall be located in a stable stratum, so as to avoid crossing the section with extremely complicated engineering geology and hydrogeology and serious adverse geology. When it is necessary to pass, there should be practical and reliable engineering measures.
2. For the long tunnel crossing the watershed, the route direction and plane position should be determined on the basis of large-scale geological mapping and comprehensive geological exploration. For the crossing points that may be crossed, different crossing elevations and corresponding route layout schemes should be drawn up, and comprehensive technical and economic comparison should be made in combination with factors such as route direction, construction and operation conditions.
3. When the line is along the river and along the mountain, when crossing the tunnel, its position should move inward to the mountain side to avoid the adverse influence of tunnel wall on tunnel stability, river scouring and bad geology. The long tunnel scheme should be compared with the short tunnel group or bridge tunnel group scheme in terms of technology and economy.
4. The tunnel entrance should not be located in low-lying valleys with poor geology, difficult drainage, or unstable cliffs, such as landslides, collapses, rock piles, dangerous rock falls and mudslides. The principle of "entering early and leaving late" should be followed, and the entrance position should be selected reasonably to avoid the formation of high slopes and high slopes at the entrance.
5. For the tunnel near the reservoir area, the design elevation of the entrance shoulder should be no less than 0.5m of the calculated flood level (including wave height and backwater height) of the reservoir. At the same time, we should pay attention to the adverse effect of the collapse of the reservoir wall caused by long-term immersion of the reservoir water on the stability of the tunnel, and take corresponding engineering measures.
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