ELI5: Why are tunnels round? : r/explainlikeimfive (reddit.com)
Tunnels are often designed with circular cross-sections for various practical reasons:
1. **Structural Stability:** Circular shapes are inherently strong and distribute forces evenly. This is
important for tunnels, which need to withstand the pressure from the surrounding soil, rock, or water.
Circular tunnels can better resist external pressures, reducing the likelihood of collapse or deformation.
2. **Uniform Stress Distribution:** Circular tunnels distribute stress uniformly along their walls. This
means that no particular point along the tunnel's circumference experiences significantly higher stress,
reducing the risk of weak points forming that could lead to structural failure.
3. **Efficient Use of Material:** Circular shapes provide efficient use of materials when constructing
tunnels. Other shapes, like squares or rectangles, have corners that can concentrate stress and require
additional reinforcement, making them less efficient in terms of material usage.
4. **Ease of Excavation:** Circular tunnels are often easier to excavate because tunnel-boring
machines, which are commonly used in tunnel construction, are designed to create circular openings.
This reduces the complexity of excavation and makes the process more streamlined.
5. **Smooth Flow:** If a tunnel is intended for the passage of fluids (such as water or sewage), a
circular shape minimizes flow resistance and turbulence. This is important for maintaining efficient flow
rates and preventing clogs.
6. **Minimal Surface Area:** Among all shapes, a circle has the smallest perimeter for a given area. This
means that, compared to other shapes, circular tunnels have relatively less surface area exposed to
external factors such as soil pressure or water infiltration.
7. **Historical and Practical Precedent:** Circular tunnel designs have been used for centuries in various
underground structures, from mines to catacombs to transportation tunnels. The long history of circular
tunnels has led to a wealth of knowledge and experience in designing, constructing, and maintaining
them.
It's worth noting that while circular tunnels are common, there are instances where other shapes might
be more appropriate. For example, rectangular or horseshoe-shaped tunnels might be used when
accommodating certain types of transportation or when specific geological or engineering
considerations dictate an alternative shape.
While circular tunnels are common, there are instances where other shapes might be used. For instance,
horseshoe-shaped tunnels are common in some transportation systems. However, these shapes are
often chosen based on specific engineering requirements, geological conditions, or functional
considerations..