What is the invert of a tunnel? The "invert of a tunnel" refers to the lowest internal surface of the tunnel, essentially the bottom curve or flat section of its interior. It is part of the tunnel lining and is the counterpart to the tunnel's "crown", which is the highest internal point.

　　In physical terms, a tunnel's "inverse" might not have a direct equivalent in everyday language since tunnels are typically defined by their specific function and structure: they are underground passageways that allow transportation through otherwise impenetrable barriers like mountains or under bodies of water.

　　However, if we approach this from a conceptual perspective, considering opposites or alternatives, several interpretations could emerge:

　　1. Surface Route: The inverse of a tunnel, which operates below ground level, would be any type of surface route, such as roads, highways, bridges, or overpasses. These structures operate on the surface or above it, providing alternative paths for travel without the need to dig beneath.

　　2. Overhead Passage: An overhead passage, such as skyways or elevated walkways, could also serve as an opposite to a tunnel. While tunnels aim to connect points by cutting through obstacles at lower levels, overhead passages achieve connectivity by rising above obstructions.

　　The invert often carries structural significance and functional roles, such as:

　　- Structural Support: It helps stabilize the tunnel and distribute the loads from the surrounding earth or rock.

　　- Drainage: In tunnels used for transportation or utilities, the invert may include a drainage channel or sump to manage water accumulation.

　　- Track or Roadbed Support: In transportation tunnels, the invert may house tracks for trains or the roadbed for vehicles.

　　Its design typically aligns with the overall shape and function of the tunnel, whether circular, elliptical, or rectangular.