Manual shield tunnelling was an early method that used a protective shield to safeguard labourers while they excavated the tunnel face.
The system was crucial for soft, unstable ground (such as the clay beneath London) and was famously used in the construction of the original London Underground.Tunnels are constructed using various methods, with the choice depending on factors such as ground conditions (soft clay vs. hard rock), water presence, tunnel length, diameter, depth, and the final use.
The shield was inched forward incrementally, and workers would manually dig the material out ahead of it.
As the shield advanced, workers would progressively install prefabricated sections of the tunnel wall (often cast-iron or brick lining) to replace the space vacated by the shield.
