What is a Soft Rock TBM? A soft rock TBM is a machine specifically designed for tunnel excavation in softer, fragmented geological conditions or layers with high moisture content. Compared to hard rock TBMs, soft rock TBMs are more suited to construction tasks in non-solid layers like mudstone, sand, clay, and similar materials.
I、 Composition of a Soft Rock TBM
A soft rock TBM usually consists of the following components:
1. Cutterhead: Located at the front of the machine, it is equipped with replaceable cutting tools and scrapers to cut and break the rock. The cutterhead's design is flexible and can be adjusted based on the geological conditions.
2. Propulsion System: Responsible for pushing the TBM forward, the propulsion system usually consists of hydraulic cylinders or other driving mechanisms that provide enough force for the TBM to advance through soft rock.
3. Support System: This system provides support to the excavated tunnel to prevent collapse. Depending on geological conditions, different support methods may be used, such as sprayed concrete, rock bolts, or steel arches.
4. Muck Removal System: This system transports the excavated material out of the tunnel. It typically uses conveyors, screw conveyors, or other equipment to efficiently transport the debris.
5. Electrical Control System: Controls various parts of the TBM to ensure automated operation. This system can adjust parameters like tunneling speed, cutting force, and propulsion force based on construction requirements.
II、Features of a Soft Rock TBM
1. Cutterhead System: Soft rock TBMs are equipped with a cutterhead, and its cutting tools (such as scrapers and disc cutters) effectively break soft rock and transform it into material that can be conveyed.
2. Propulsion System: Provides thrust through hydraulic or mechanical means, allowing the machine to move forward in the ground.
3. Support System: Includes mechanisms for assembling tunnel segments and anchoring devices to immediately support the freshly excavated space and prevent collapse.
4. Muck Disposal System: Uses screw conveyors or similar equipment to remove the debris, keeping the working face clean.
5. Guidance System: Uses advanced measurement techniques to ensure precision in tunnel alignment.
6. Environmental Measures: Some models come with dust suppression, noise reduction, and wastewater treatment facilities to minimize environmental impact.
III、Working Principle of a Soft Rock TBM
The working principle of a soft rock TBM involves cutting and breaking the soft rock using the cutterhead's tools and scrapers. The broken material is then transported out of the tunnel by the muck removal system, while the propulsion system continuously pushes the TBM forward, and the support system ensures the tunnel remains stable.
The specific process is as follows:
1. Cutting and Breaking
- The cutterhead rotates at high speed, driven by an electric motor or hydraulic motor. The tools and scrapers on the cutterhead contact the soft rock, cutting and breaking it. The cut material is directed into the muck removal system through openings in the cutterhead.
- The design of the cutterhead and the selection of cutting tools are adjusted according to geological conditions. For softer rock, larger tools and wider scrapers can be used for higher efficiency, while smaller tools and narrower scrapers are selected for harder rock to increase cutting force.
2. Muck Removal
- The broken material is transferred through the openings on the cutterhead into the muck removal system, typically consisting of conveyors or screw conveyors. This system transports the material out of the tunnel to a muck bin or transport vehicle.
- The muck removal system must be matched with the cutting capacity of the TBM to ensure timely removal of material and avoid accumulation, which could affect construction progress.
3. Tunneling
- The TBM's propulsion system pushes the machine forward using hydraulic cylinders or other devices. The propulsion force is adjusted based on the geological conditions and the weight of the machine to ensure smooth advancement through soft rock.
- The tunneling speed must be coordinated with the cutting speed and muck removal capacity to ensure continuous and efficient operation.
4. Supporting Operations
- As the TBM advances, the support system provides timely reinforcement to the excavated tunnel. Depending on geological conditions, support methods may include sprayed concrete, rock bolts, or steel arches.
- The support system's speed must match the TBM’s tunneling speed to ensure the tunnel’s stability and construction safety.
IV、Application Scenarios for Soft Rock TBMs
1. Excavation of tunnels for subway systems, highways, and water conservancy projects.
2. Mining roadway excavation and underground mine development.
3. Municipal infrastructure projects, such as the installation of drainage or gas pipelines.
Today's soft rock TBMs are evolving towards more intelligent, larger-scale, and efficient machines. For instance, integrating more sensors and automation components improves operational efficiency and safety. Advanced materials and technology are being used to enhance tool performance and extend service life. Additionally, there are ongoing efforts to explore environmentally friendly solutions to make construction more sustainable and green.