The Earth Pressure Balance Tunnel Boring Machine (EPB TBM) is an advanced engineering machine used for tunnel excavation. Below is an introduction to the structure, working principle, and process of the EPB TBM.
I. Working Principle
The EPB TBM cuts the soil in front using a rotating cutter head. The cut soil enters the chamber, where it is discharged by a screw conveyor. By controlling the screw conveyor's speed and adjusting the thrust of the shield machine, the pressure in the chamber is kept balanced with the pressure of the soil and water at the excavation face. This balance maintains the stability of the excavation face, preventing collapse and surface subsidence.
II. Structural Components
1. Cutter Head: Located at the front of the shield, the cutter head is made up of tools and a panel, used for cutting soil. The design of the cutter head and tool arrangement varies based on different geological conditions.
2. Chamber: Stores the cut soil. The chamber is equipped with a mixing device to prevent soil consolidation and improve soil flow.
3. Screw Conveyor: Transports the soil from the chamber to the rear conveyor belt or muck car. The screw conveyor's speed can be adjusted to control the pressure inside the chamber.
4. Shield Body: Includes the front shield, middle shield, and rear shield, forming the main structure of the tunnel boring machine. It provides support and protection, with the propulsion system and sealing system installed on it.
5. Propulsion System: Composed of jacks that push the shield forward. The thrust and speed of the propulsion system can be adjusted as needed.
6. Segment Erector: Used to install tunnel lining segments. The segment erector rotates and moves within the shield body to accurately place the segments on the tunnel wall.
7. Backup System: Includes conveyor belts, ventilation systems, power supply systems, and water supply and drainage systems, providing logistical support for the tunnel boring machine.
III. Characteristics
1. Wide Applicability: Suitable for various geological conditions, including soft soil, hard soil, and sand gravel.
2. High Construction Speed: The mechanized construction method allows for much faster excavation than traditional mining methods.
3. Minimal Environmental Impact: By controlling soil pressure, surface subsidence and the impact on surrounding buildings are effectively reduced.
4. High Safety: Construction inside the shield body ensures relative safety for personnel.
5. High Degree of Automation: Automated control reduces manual operation, increasing construction efficiency and quality.
IV. Working Process of the EPB TBM
First, the cutter head begins rotating, cutting the soil ahead. The cut soil enters the chamber. The chamber's pressure is balanced with the soil and water pressure at the excavation face by precisely controlling the screw conveyor's speed and adjusting the shield's propulsion speed. This balance prevents dangerous situations like collapses.
Next, the soil in the chamber is discharged via the screw conveyor and transported out of the tunnel by conveyor belts or muck cars. Simultaneously, the powerful thrust of the shield jacks moves the entire machine forward.
During excavation, tunnel lining segments are assembled to form the tunnel structure. This assembly must ensure precision and good sealing to guarantee tunnel quality and waterproof performance.
Additionally, depending on the soil properties and excavation conditions, materials such as foam or bentonite slurry can be injected into the chamber to improve soil flow and stability, enhance excavation efficiency, and reduce wear on the shield.
Throughout the construction process, auxiliary systems like ventilation, power supply, and water supply and drainage systems must operate to ensure safety and smooth progress.
V. Application Fields
The EPB TBM is widely used in the construction of urban subways, railway tunnels, highway tunnels, and water conservancy tunnels. With continuous technological advancements, the performance and applicability of EPB TBMs are expanding.