Detailed explanation of the working principle of the tunnel lining trolley

A tunnel lining trolley, also known as a formwork trolley or a segment erector, is a crucial piece of equipment used in the construction of tunnels, particularly for the installation of the final lining. Its working principle can be broken down into several key stages and components.

Tunnel Lining Trolley Working Principle

1. Purpose of the Tunnel Lining Trolley

The primary purpose of the tunnel lining trolley is to provide a movable, adjustable support structure for the formwork (mould) into which concrete is poured to create the tunnel lining. It also often facilitates the handling and precise positioning of precast concrete segments in segmental lining methods.

2. Key Components and Their Functions

Main Frame/Structure: This is the robust, load-bearing backbone of the trolley, typically made from heavy-duty steel. It must be strong enough to support the weight of the formwork, fresh concrete, and any associated machinery.

Traveling Mechanism: The trolley needs to move along the tunnel. This is usually achieved with electric motors driving wheels or tracks that run on rails laid on the tunnel invert (floor). This allows the trolley to advance to the next section after a lining pour is completed.

Hydraulic Jacks and Cylinders: These are critical for the precise positioning and adjustment of the formwork.

Vertical Jacks: Used to lift and lower the entire formwork assembly to the correct height and ensure proper alignment with the tunnel axis.

Horizontal Jacks/Telescopic Beams: Used to expand or retract the formwork to match the exact radius and cross-section of the tunnel. These also enable the formwork to be “struck” (retracted) from the cured concrete after a pour.

Transverse Jacks: Used for lateral alignment, ensuring the formwork is centered within the tunnel.

Formwork (Mould): This is the actual surface against which the concrete is cast. It’s typically made of steel plates, precisely curved to the desired tunnel profile. The formwork is often segmented longitudinally and circumferentially to allow for easier stripping and adjustment.

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