Closed shield tunnel boring machines

Service Specifications for Closed-Shield Tunnel Boring Machines (EPB and Slurry)

Closed-shield tunnel boring machines (EPB and slurry) are used in soil conditions where it is necessary to control the pressure from the front to ensure ground stability and minimize surface settlement. This service is defined by the following technical parameters and application criteria:

• Main applications: Microtunnels and mechanized tunnels in loose, sandy, silty, clayey, mixed, or saturated soils; projects beneath sensitive urban areas, existing infrastructure, waterways, roads, and areas at risk of landslides.

• Types of shields:
– EPB (Earth Pressure Balance): It works by balancing the pressure at the face using the excavated material that has been processed.
– Slurry / Hydro-shield: It uses pressurized slurry to stabilize the face in granular, saturated, or high-water-pressure soils.

• Compatible land conditions: Non-cohesive soils, materials prone to collapse, saturated sands, mixed soils, and conditions with a high water table. The choice between EPB and slurry depends on the permeability, strength, and behavior of the soil.

• Range of diameters and lengths: Suitable for microtunnels and medium- or large-diameter tunnels, with lengths determined based on the construction method, the jacking system, and the structural design of the lining.

• Construction method: Mechanized excavation in a pressurized chamber, with control of torque, thrust, and advance; material extraction via an auger (EPB) or a slurry circuit and separation plant (Slurry). The lining is typically constructed using reinforced concrete segments or driven pipe, depending on the project.

• Civil Engineering and Logistics Requirements: Shafts or tunnel portals with sufficient space for the tunnel boring machine, grouting systems, a slurry/bentonite plant, electrical equipment, and ventilation. Requires areas for the storage, assembly, and transport of tunnel segments or pipe.

• Control and Guidance Systems: Continuous monitoring of chamber pressure, thrust, cutting torque, excavated volume, support pressures, and alignment using lasers or gyroscopes, ensuring geometric tolerances and stability.

• Quality control and safety: Monitoring of excavation parameters, pressure balance control, face stability, joint sealing, ventilation, safe access, and compliance with HSE protocols in confined spaces and urban environments.