Tunnel construction, a complex and costly engineering endeavor, has gained prominence in response to the growing need for reduced travel time between distant locations. Despite its historical roots dating back to 1843, when the first underwater tunnel connected the River Thames banks in London, tunneling projects often face financial setbacks and technical challenges.
Tunnel failures pose significant risks, necessitating meticulous planning and surveying to mitigate potential issues. This article explores various types of tunnel failures, their underlying causes, and the remedial measures employed to prevent and address them.
Excessive pore water pressure, often triggered by heavy rainfall, can lead to ground collapse near tunnel portals.
The umbrella technique, a method that reinforces the material surrounding the tunnel periphery, mitigates the risk of sudden collapses (see Figure 1).
Continuous water ingress at the tunnel base reduces soil bearing capacity, causing settling and subsequent wrapping and twisting of the tunnel support system.
To protect the tunnel invert, a systematic drainage system design is crucial, focusing on the portion subjected to maximum stress (see Figure 2).
In mountainous regions, where Tunnel Boring Machines (TBM) may be impractical, blasting is an alternative. Incorrect blasting designs can result in rock mass squeezing and bursting, risking tunnel collapse.
A well-designed blasting system, accounting for parameters like burden, stemming length, and bench spacing, is essential for successful tunnel excavation (see Figure 3).
Post-blasting, cavities may form in the rock mass. Failure to identify these cavities before advancing each tunnel section can lead to accidents and tunnel failures.
Trail holes before advancement, and if cavities are detected, fill them with bentonite slurry.
Blasting can loosen faults and fractures, exerting excessive shear force on tunnel peripheries, leading to shear failure and concrete lining cracks.
Monitor fault spacing with appropriate equipment, change tunnel alignment if possible, and employ chemical stabilization (grouting) for faults exceeding permissible limits (see Figure 5).
Swelling clay soil above tunnel crowns, subjected to hydrothermal pressure, can increase soil particle volume, causing heaving at the pavement surface base.
Utilize rock bolts or anchor bolts around the tunnel periphery and below the pavement surface to reduce material flow and counteract heaving (see Figure 6).
By understanding these tunnel failure types and implementing appropriate corrective measures, engineers can enhance the safety and success of tunneling projects, ensuring efficient connectivity without compromising financial stability.