Tunnel Boring Machines (TBM) Intro

Introduction to Tunnel Boring Machines (TBM)

• TBM operation basics are covered in this document.

TBM Overview

• The 海瑞克 (Herrenknecht) TBM, a German design, weighs 520 tons and is 82 meters long.
• TBMs are divided into "car heads" (shield) and "carriages" (trailing equipment).
• The "car head" is the shield body, and the "carriage" is the trailing equipment.
• Trailing equipment is installed on the 5 subsequent trolleys behind the shield body.
• The shield body includes components like the main shield, jacks, segment erector, cutter head, power unit, electrical equipment, piping, traction frame, grouting system, foam system and backfilling system.
• Over 20 parts make up the shield body.
• TBM operation occurs within the protection of the shield.
• TBM is a combination of "shield" and "spear," with the cutter head acting as the "spear."
• The cutter head has 92 picks to adapt to geological conditions using rolling bits, scrapers and replaceable ripping picks for both hard and soft soil.

Operating Principles and Components

• Fixed agitator blades on the cutter head mix additives like mud, water, and foam with the excavated soil to improve plasticity, fluidity, and water resistance.
• A sealed bulkhead creates a soil bin between the shield and excavation face.
• Soil bin is used to accumulate excavated material and apply pressure to stabilize the excavation surface and protect workers inside.
• The shield body has systems for propulsion, soil transport, segment transport/erection, access, etc.
• 32 tunnel jacking devices are installed around the circumference of the TBM's rear.
• The 14 jacks exert a total propulsion of 34,210 kN, equivalent to 10 locomotive traction forces.
• The pressure difference between the soil bin and tunnel can reach 2 atm (20m water depth), preventing water inflow.
• Personnel entering the soil bin must undergo slow pressurization in the access chamber until pressure equals the soil bin's pressure.
• Decompression is required when exiting high-pressure environments.
• Access chambers are equipped with lighting, pressure gauges, valves, clocks, silencers, and chairs.

TBM Operation and Personnel

• If a worker cannot continue working, they are decompressed in the main chamber, and medical staff enter an auxiliary chamber for compression to aid the injured worker as quickly as possible.
• Hydraulic, electrical, and control systems, alongside post-support systems, work in coordination for TBM operation.
• Two operators, one chief and one assistant, manage a TBM during operation.
• To run reliably, one backup operator, 10 slag removers, 6 segment transport/installers, 2 gantry crane operators and electricians are required.
• TBMs operate in two shifts, using less than 40 people per shift.
• The whole team, including the project manager, safety officer, material procurement staff, and logistics staff, consists of 100+ people.

Hard Rock TBMs

• TBMs are the most advanced tunneling machines, using mechanical thrust and shear force to break rock.
• High-pressure hydraulic cylinders provide thrust to force cutting tools into the rock mass.
• Thrust from the hydraulic cylinder determines TBM advancement speed.
• Cutting is performed by disc cutters, cutting tools, and scraper tools on the cutter head.
• The cutter head's rotation provides the torque and speed for tunneling, mucking, lining, grouting, and laser guidance.
• TBMs minimize disturbance to surrounding rock, creating smooth tunnel surfaces with less overbreak.
• TBM advantages include speed, quality, cost-effectiveness, and safety in water conservancy, hydropower, urban construction, and transportation.
• TBMs are divided into rock tunnel boring machines with single or double shields used for rock tunnel construction.
• Initial support involves rock bolts and shotcrete, with optional secondary lining or precast concrete segments.
• Other TBMs are shield machines that include earth pressure balance or slurry types used for soil, sand or complex geology.
• Shield machines don’t need initial support, but use segments.
• TBMs are suited for medium-hard rock (50-150 MPa uniaxial compressive strength).
• Exceeding 150 MPa increases tool wear and cost.
• When advancing through weak rock like soil, faults, or karst caves, the machine is likely to sink.
• TBM's rock breaking principles, technology and efficiency have advanced rapidly since the 1960s.
• Small/medium diameter TBMs are now mature and widely used.

Function and Composition of Shield Machines

• Shield machines break the tunnel face mechanically and remove the broken material.
• Tunnelling with shield machines is automated and saves manpower, provides speed, single-pass construction, weatherproof operation.
• Shield machines control ground settlement, minimize impact on surface structures, and allow underwater excavation without affecting surface traffic.
• Shield machine construction is economical for long and deeply buried tunnels.
• Shield machines are used in underground excavation, preventing collapse.
• Within the machine, tunnelling can be performed safely.
• Construction starts with a shaft or foundation pit, into which the machine is lowered and installed.
• The shield machine then tunnels from the shaft wall along the designed alignment to another shaft or tunnel end.
• Three components are important for shield machine construction: face stabilization, excavation and soil removal, lining.

TBM Advancement

• Hydraulic motors drive the cutter head, and the TBM's propulsion cylinders advance it.
• As the cylinders push the machine forward, the cutter head rotates, filling the soil bin.
• A screw conveyor removes the muck onto a belt conveyor, which transports it to containers and then to the surface.
• Soil removal and speed are controlled: when the soil bin fills, resistance increases.
• Face stability is maintained when the soil pressure in the bin equals the earth and water pressure on the face.

Segment Assembly

• After excavating a certain distance, the segment erector assembles precast segments to form the tunnel lining.

TBM Classification

• TBMs are classified by soil type: soft soil, hard rock, or mixed ground.
  • Soft soil TBMs work in unconsolidated soft soil, weathered rock, and use scraper bits.
  • Hard rock TBMs are for dense rock, use roller bits, and need no scraper bits.
  • Mixed ground TBMs incorporate both types of tools.
• TBMs are also classified by working method as slurry type, earth pressure balance type, etc.
  • Slurry TBMs stabilize using pressurized slurry (bentonite suspension).
  • Earth Pressure Balance TBMs use soil as a stabilizing medium (additives are added).
  • Earth pressure is adjusted by controlling the cutter head rotation.

TBM Components

• The TBM consists of a cylindrical steel structure that advances along the tunnel axis.
• The shell is called a shield, offering temporary support to the tunnel section while soil is excavated.
• The shield protects from surrounding earth pressure and water.
• Excavation, soil removal, and lining take place under the shield's protection.
• Main components include the shield body, cutter head drive, double chamber airlock, segment erector, and soil removal system.

Shield Body Components

• The shield body consists of the front, middle, and rear shields.
• All three components are cylindrical with a diameter of 6.25m.
• The front shield and pressure bulkhead are welded together to support the cutter head drive and isolate the soil bin.
• Jacks apply pressure to the excavation face through the bulkhead for support.
• Earth pressure sensors are installed to measure pressure at different heights in the bin.
• The jacking device is on the rear with 30 hydraulic jacks.
• The jacks push against segments already installed, moving the TBM forward.
• Four groups of jacks control movement, allowing the machine to turn.
• The rear shield via hydraulic cylinders are connected with the middle shield for steering.

Cutter Head

• The cutter head is a rotating disc with material slots that cuts soil.
• The opening ratio is about 28%, diameter is 6.28m.
• A flanged plate connects the cutter head to the drive.
• Hard rock or soft soil tools can be installed based on soil conditions.
• An overcutting knife, operated by a hydraulic cylinder and extend radially to enlarge the cut diameter, is along the cutter.
• All types of cutting tools are bolted on and replaceable from the soil bin.

Cutter Head Drive

• A rotating joint transmits foam, bentonite fluid, and hydraulic oil to the overcutting knife cylinder.
• The cutter head has clockwise and counterclockwise rotation at 0-6.1 r/min which is achieved with hydraulic motor.
• The cutter head drive with variable axial piston motors combined with water-cooled gearboxes.
• A brake is installed in one of the gearbox sets for cutter head braking.
• A volumetric screw hydraulic pump is installed to drive the main gear oil supply and lubricate the main gearbox to cool it.

Airlocks

• The dual-chamber airlock is located on the front shield, consisting of front and main chambers.
• It used where personnel perform in the soil bin.
• Airlocks are needed to avoid face collapse or regulate the soil pressure.
• The pressure in the airlock is set for normal and excavation pressure.
• Only qualified personnel under high pressure can go through through airlocks.
• If workers need into the soil bin at pressure, they enter the chamber, closing the front chamber and main chamber.
• Airlock pressure will be increased, and both pressures need to be same before opening the gate to the soil bin and enter.
• If workers need to exit the chamber, that worker would enter the main chamber first, and another worker would enter the front chamber.
• The airlock will pressurize the chamber to the same pressure, thus allowing for exiting to the operation zone.

Segment Erection Equipment

• The segment erector comprises a beam, support, rotating frame, and erection head.
• The erector uses a flange connection on the rear of the middle shield.
• Rollers are installed on the beam through the channel, where gears are rotated on both sides.
• The erector head is connected to the rotating frame using hydraulic cylinders and crossbeams.
• Two hydraulic cylinders move the erector, rotating frame, and head along the tunnel axis.
• Slew motors drive bearings to rotate and angle the erector and erection head.
• Hydraulic cylinders lift the erection head and allow it to grab tubing; it can be adjusted around 6 axes.
• A wired or wireless control can be used.
• Each ring uses 6 segments (three standard, two adjacent, one cap which has multiple positions) is installed.
• The segments are sealed with gasketed materials installed through bolts.

Discharge System

• The discharge system includes a screw conveyor and belt conveyor driven by motors.
• Soil from the soil bin is transported to a belt conveyor at the conveyor head.
• This conveys it the length of the fourth section, which can be transported onto bogies.
• The bogies are transported to a crane and hauled out.
• The screw conveyor is equipped with front and rear brakes, the front brake is locked to stop the TBM in case of a power shutdown.
• The rear brake is closed down during excavation or repair, to limit the force of excavation.

Additional Equipment

• Back equipment components: Segment transport equipment including a fourth stage, but also: Operator room/Electrical Component/Hydraulic component/Grouting Equipment/Foam Equipment/Bentonite Components/Circulation and ventilation equipment.
• Segment transport includes small transport cars, but also: Electric hoists and connecting bridges including gantry cranes.
• There is a control room where machines are installed, an automatic control system, laser system, monitors and more.
• Two units contain hydraulic pumps that provide power for the disk, lubrication pumps, hydraulic equipment, lubrication equipment, the segment assembly and more.
• The cylinders, lubrication pumps and the rest are all installed with water cooled equipment.
• The grease pump provides grease for 12 lines during excavation, as well to prevent the injection of slurry behind the pipe sheets.
• Lubricating systems pump oil into the hull.
• It injects this into three lip seals - to grease the lip seal work areas and help to prevent contamination.
• The mixing cylinders have 2 air compressors, 1 m3 air tank, electrical cabinets.
• The system can provide eight bar for earth improvement and has appropriate mixing levels.

Technical Parameters and Key Definitions

• The following table lists various parameters related to the shield machine
• Terms include: Earth Pressure Balance shield, Cutters, Cutter Drive Unit, Segments, Segment Assembly Machines, Spiral Conveyors, Shield Shell.
• The table defines several factors for these different terms.