Tunnel Boring Machine (TBM) Fundamentals and Selection

Geotechnical Investigation and Ground Characterization

• Understanding the principles of soil and rock mechanics as applied to tunneling. This includes detailed analysis of:
• Soil types and their properties: grain size distribution, Atterberg limits, permeability, consolidation characteristics, and shear strength parameters (cohesion and friction angle).
• Rock mass classification systems: Rock Quality Designation (RQD), Geological Strength Index (GSI), and Q-system. Assessment of rock strength, fracture frequency, weathering grade, and joint characteristics (orientation, spacing, persistence, roughness, and infilling).
• Groundwater conditions: hydrogeological investigations, permeability testing (e.g., Lugeon tests, slug tests), and groundwater chemistry analysis to assess potential for corrosion and erosion.
• Geophysical methods: seismic refraction, ground penetrating radar (GPR), and electrical resistivity tomography (ERT) for subsurface profiling and anomaly detection.
• Borehole logging: comprehensive analysis of borehole data, including geological logs, geotechnical test results, and geophysical logs, to create a detailed ground model.

TBM Types and Their Suitability

• Hard Rock TBMs:
• Disc Cutters: Understanding the mechanics of rock cutting with disc cutters, including cutter forces, wear rates, and cutterhead design optimization. Examples include single shield and double shield TBMs for varying rock conditions.
• Gripper Systems: Analysis of gripper systems for TBM advance, including gripper force calculations, gripper pad design, and gripper maintenance procedures.
• Soft Ground TBMs:
• Earth Pressure Balance (EPB) TBMs: Controlling face stability in soft ground by applying controlled earth pressure. Understanding the principles of soil conditioning with additives such as polymers and bentonite to improve soil workability and reduce permeability.
• Slurry TBMs: Maintaining face stability by using a slurry support system. Understanding the principles of slurry preparation, injection, and recovery, as well as the control of slurry pressure and viscosity.
• Mixshield TBMs: A hybrid approach suitable for mixed ground conditions, combining features of both EPB and slurry TBMs.
• Selection Criteria: Evaluating the geotechnical conditions, tunnel geometry, advance rate requirements, and environmental constraints to select the most appropriate TBM type.

TBM Operation and Control

TBM Assembly and Launching

• Assembly Procedures: Detailed step-by-step procedures for assembling the TBM at the launch shaft, including the installation of the cutterhead, drive motors, hydraulic systems, and backup systems.
• Launching Techniques: Techniques for launching the TBM into the tunnel, including the use of thrust rings, jacking systems, and guidance systems.
• Initial Ground Support: Implementing initial ground support measures, such as shotcrete and rock bolts, to stabilize the tunnel face and prevent collapse.

TBM Driving Parameters and Optimization

• Penetration Rate: Controlling the penetration rate of the TBM based on ground conditions, cutterhead RPM, and thrust force. Analyzing the relationship between penetration rate, cutter wear, and advance rate.
• Cutterhead Speed and Torque: Optimizing the cutterhead speed and torque to maximize advance rate while minimizing cutter wear and power consumption. Examples of how to adjust parameters for different rock strengths.
• Thrust Force: Controlling the thrust force applied to the TBM based on ground conditions and cutterhead performance. Monitoring thrust force to detect changes in ground conditions and potential problems with the TBM.
• Steering and Guidance: Implementing precise steering and guidance systems to maintain the TBM on the planned alignment. Analyzing survey data and making adjustments to the TBM's steering system as needed.
• Real-time Monitoring: Utilization of sensors and data acquisition systems to monitor TBM performance, ground conditions, and environmental parameters in real-time.

Ground Support and Tunnel Lining

• Segmental Lining: Installing precast concrete segments to create a permanent tunnel lining. Understanding the principles of segment design, joint sealing, and ring erection.
• Shotcrete Application: Applying shotcrete to the tunnel walls to provide immediate ground support and prevent collapse. Understanding the principles of shotcrete mix design, application techniques, and curing procedures.
• Rock Bolting: Installing rock bolts to reinforce the tunnel walls and prevent rock falls. Understanding the principles of rock bolt design, installation techniques, and testing procedures.
• Grouting Techniques: Using grouting to fill voids behind the tunnel lining and stabilize the ground. Understanding the principles of grout mix design, injection techniques, and pressure control.

TBM Maintenance and Repair

Cutterhead Maintenance and Replacement

• Cutter Inspection: Performing regular inspections of the cutterhead to identify worn or damaged cutters. Understanding the different types of cutter wear and their causes.
• Cutter Replacement: Replacing worn or damaged cutters using specialized tools and equipment. Understanding the procedures for cutter removal, cutter installation, and cutter torqueing.
• Cutterhead Refurbishment: Refurbishing the cutterhead to extend its lifespan and improve its performance. Examples of hardfacing and cutter lacing techniques.
• Cutter Management: Implementing a cutter management system to track cutter usage, wear rates, and replacement costs.

Hydraulic and Electrical System Maintenance

• Hydraulic System Inspection: Inspecting the hydraulic system for leaks, damage, and wear. Understanding the principles of hydraulic system operation and maintenance.
• Hydraulic System Repair: Repairing or replacing damaged hydraulic components, such as pumps, valves, and cylinders. Understanding the procedures for hydraulic system troubleshooting and repair.
• Electrical System Inspection: Inspecting the electrical system for damage, corrosion, and loose connections. Understanding the principles of electrical system operation and maintenance.
• Electrical System Repair: Repairing or replacing damaged electrical components, such as motors, generators, and control panels. Understanding the procedures for electrical system troubleshooting and repair.

Preventative Maintenance Strategies

• Maintenance Scheduling: Developing a preventative maintenance schedule based on TBM operating hours, ground conditions, and manufacturer recommendations.
• Lubrication Procedures: Implementing proper lubrication procedures to minimize wear and extend the lifespan of TBM components. Understanding the different types of lubricants and their applications.
• Component Inspection: Performing regular inspections of critical TBM components, such as bearings, seals, and gears, to identify potential problems early on.
• Data Analysis: Analyzing TBM operating data to identify trends and predict potential failures. Implementing predictive maintenance strategies to minimize downtime and maximize TBM availability.

TBM Refurbishment and End-of-Life Management

Assessment of Refurbishment Needs

• Condition Assessment: Conducting a comprehensive assessment of the TBM's condition to identify components that need to be refurbished or replaced. This includes visual inspections, non-destructive testing, and performance testing.
• Cost-Benefit Analysis: Performing a cost-benefit analysis to determine whether it is more cost-effective to refurbish the TBM or purchase a new one. Considering the cost of refurbishment, the remaining lifespan of the TBM, and the potential for increased productivity.
• Refurbishment Planning: Developing a detailed refurbishment plan that outlines the scope of work, the schedule, and the budget. This includes identifying the required resources, such as manpower, equipment, and materials.

Refurbishment Processes

• Component Overhaul: Overhauling major TBM components, such as the cutterhead, drive motors, and hydraulic systems. This includes disassembling the components, cleaning and inspecting them, repairing or replacing damaged parts, and reassembling them.
• Structural Repairs: Repairing any structural damage to the TBM, such as cracks or corrosion. This includes welding, patching, and reinforcing the TBM's frame and body.
• Control System Upgrades: Upgrading the TBM's control system to improve its performance and efficiency. This includes installing new sensors, software, and automation systems.
• Testing and Commissioning: Testing and commissioning the refurbished TBM to ensure that it is operating properly. This includes performing load tests, function tests, and safety checks.

Decommissioning and Recycling

• Decommissioning Procedures: Implementing safe and environmentally sound decommissioning procedures for TBMs that have reached the end of their useful life. This includes removing hazardous materials, dismantling the TBM, and preparing it for recycling.
• Recycling Options: Exploring recycling options for TBM components, such as steel, copper, and aluminum. Working with recycling companies to ensure that the TBM is recycled in an environmentally responsible manner.
• Disposal Methods: Implementing proper disposal methods for TBM components that cannot be recycled. This includes landfilling, incineration, and other waste management techniques.
• Environmental Considerations: Considering the environmental impact of TBM decommissioning and recycling activities. Implementing measures to minimize pollution and protect the environment.