Temporary bridges in TBMs serve as structural supports that stabilize the tunnel face and facilitate safe assembly, alignment, and material handling during excavation.

Role and Purpose

Temporary bridges, often referred to as shoring systems or temporary supports, are critical in TBM operations for several reasons:

• Stabilization of Excavation: As the TBM advances, the surrounding soil or rock may be unstable. Temporary bridges provide immediate support to the tunnel walls and roof, preventing collapses and ensuring the safety of workers and equipment inside the tunnel (Ferrovial) .
• Support for Shield and Cutterhead: In soft or mixed ground conditions, TBMs use shields that temporarily hold the ground. Temporary bridges help distribute loads from the shield and maintain the correct alignment of the cutterhead, ensuring precise excavation (Ferrovial) .
• Facilitation of Assembly and Maintenance: TBMs are transported in modular components and often partially assembled within the launch shaft. Temporary bridges provide platforms for workers to access different sections of the machine safely during assembly, installation, and maintenance (Enerpac) .
• Material Handling and Transport: Excavated material (muck) is transported via conveyor systems. Temporary bridges can support these conveyors and other equipment, allowing smooth removal of debris and continuous TBM operation (Encardio) .
• Safety and Operational Efficiency: By providing a stable working platform, temporary bridges reduce the risk of accidents and allow precise positioning of TBM components, which is essential for maintaining the tunnel's planned trajectory and structural integrity (Ferrovial) .

Integration with TBM Components

Temporary bridges work in conjunction with other TBM systems:

• Shields: The outer metal chassis of shields temporarily holds the ground while the permanent lining is installed. Temporary bridges complement this by providing additional support and access (Ferrovial) .
• Hydraulic Jacks and Perimeter Supports: TBMs use jacks to push against the tunnel walls. Temporary bridges help distribute these forces evenly, preventing localized stress and deformation (Ferrovial) .
• Double-Shield TBMs: In machines that operate in both soil and rock, temporary bridges allow safe transition between excavation modes and support the assembly of the secondary shield (Ferrovial) .

Summary

Temporary bridges in TBMs are essential for structural support, worker safety, and operational efficiency. They stabilize the tunnel face, support the shield and cutterhead, facilitate assembly and maintenance, and ensure smooth material handling. Without these temporary structures, TBM operations in soft, mixed, or unstable ground would be significantly more hazardous and less precise.