Why do culvert entrances and exits under railways and highways need to be built in figure 8?

The splayed wall is mainly used to support the subgrade soil on both sides of the hole, and the subgrade soil on the upper part of the hole is supported by the end wall. The riverbed between the wing walls is paved with stones to prevent erosion, and the soil under the paved layer is stabilized by the cutoff wall below the ground at the end of the paved layer.

When a railway crosses a highway, choosing a culvert to cross the line is just like building a tunnel. Building a hole at the entrance of the tunnel should play a role in retaining soil and stabilizing slope. Intuitive along the line is conducive to reasonable drainage cost and mature technology, and is also a common means.

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