The use of Tunnel Boring Machines (TBM) has become an integral aspect of modern tunneling, offering precision and efficiency in excavation.
Among the key operational challenges is ensuring smooth and rapid TBM stepping and launching, particularly in constrained construction environments with complex geological and spatial conditions.
This article explores various stepping methods for TBMs, including single-shield, double-shield, and open-type systems, focusing on their mechanisms and applications.
Stepping Techniques for Single-Shield and Double-Shield TBMs
1. Counterbalance Frame + Semi-Circular Tube Segments + Steel Rails
This stepping method is widely applied in subway construction projects, particularly when TBMs pass through stations. The process begins with the installation of pre-embedded steel rails on a concrete curved foundation at the receiving station. The curvature aligns closely with the TBM’s shield structure. As the top extension cylinders extend, the TBM slides onto these pre-installed rails. Once the extension cylinders fully exit the circular tunnel segment, semi-circular tube segments are used to provide counterforce for further progression.
Operational Steps:
1.Gradually extend the top extension cylinders, allowing the TBM’s bottom shield to glide along the laid steel rails.
2.Upon completing one cycle of sliding, retract the cylinders and assemble semi-circular segments at the shield tail.
3.Repeat the extension and retraction process to continue the stepping operation.
2. Counterbalance Frame + Bottom Tube Segments + Steel Rails
This technique is commonly employed for TBMs used in mountainous or water conservancy tunnels. The main TBM shield is set on a curved groove slightly lower than the rear area, ensuring smooth stepping progression. Depending on the TBM’s diameter and weight, pre-embedded rails may or may not be included. Height-differential cams between the front and rear provide the necessary counterforce for the propulsion cylinders.
Operational Steps:
1.Withdraw the propulsion cylinders and place the bottom tube segment in front of the designed height cam, ensuring full contact.
2.Slowly extend the propulsion cylinders to drive the TBM forward along the curved groove.
3.Retract the cylinders and assemble the next bottom segment, ensuring all segments are securely connected.
4.Repeat this cycle to reach the starting face.
3. Rail Traveling System
This versatile system can be used with single-shield, double-shield, and open-type TBMs. It includes two main forms:
Stepping Mechanism: TBMs move along pre-installed tracks using a wheel-box system (e.g., TB880E in Xinjiang Zhongtianshan Tunnel).
Internal Force System: Hydraulic rail clamps secure the TBM to embedded rails, suitable for small-section TBMs (e.g., Hubei Shiyan and Qingdao subway projects).
Operational Steps:
1.Position the TBM on the pre-embedded tracks.
2.Use hydraulic rail clamps to secure the TBM at the start of each cycle.
3.Extend the propulsion cylinders to drive the TBM forward.
4.Release the rail clamps, retract the cylinders, and re-secure them for the next cycle.
5.Repeat until the TBM reaches the target face.
Stepping Techniques for Open-Type TBM
Open-type TBMs primarily utilize a sliding plate mechanism combined with rails or invert blocks. The stepping process is categorized into flat slide plate systems and curved slide plate systems.
1. Flat Slide Plate + Rail System
This method is widely used in water tunnels and highway tunnels, especially in gantry-supported TBMs. Unlike trolley-based systems, the rail system consists of two independent sections (left and right) that can be repositioned quickly using specialized mechanisms, allowing for reuse and enhanced efficiency.
2. Flat Slide Plate + Invert Block + Rail System
Large-diameter hard rock TBMs commonly employ this mechanism, which comprises four main components:
Lifting Mechanism: Installed on both sides of the cutterhead frame, it raises or lowers the TBM mainframe to engage or disengage the sliding plate.
Thrust Plate: Equipped with guide blocks and wheels to control the TBM’s stepping direction within a guided groove.
Pull Rods: Mounted on the drag plate, it requires adequate lubrication for smooth movement.
Saddle Frame Support: Provides reaction force for the drag plate and moves the saddle frame forward during retraction.
Operational Steps:
1.Use push-pull cylinders to drive the TBM forward by sliding on the steel plate.
2.After completing one stepping cycle, lift the TBM using the lifting mechanism and rear supports.
3.Reposition the steel plate for the next cycle.
4.Repeat until the TBM advances continuously.
Efficient TBM stepping and launching are critical for successful tunneling projects. By understanding and applying the appropriate stepping methods for single-shield, double-shield, and open-type TBMs, construction teams can overcome spatial and geological challenges, optimizing excavation efficiency. As TBM technology continues to evolve, innovative stepping techniques will further enhance tunneling operations worldwide.
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