In which situations is the use of open or closed tunnel shields recommended?

Open tunnel shields: Characteristics and applications

The open tunnel shields are those that do not have a pressurization system at the excavation face, which means that the ground is self-supporting and stable without the need for additional support. This type of excavation allows faster progress in certain types of soils and reduces the need for specialized machinery to stabilize the face.

When is its use recommended?

The use of open tunnel shields is most appropriate in situations where the terrain presents high cohesion and stability. Some of the ideal conditions include:

• Land cohesive and stableThe excavation face can be maintained without risk of collapse.

• Areas with low water tablewhere the presence of water does not affect soil stability and does not require additional containment measures.

• Excavations in urban infrastructures with controlled spaces and without major geotechnical variations, such as the installation of sewage and water supply pipes.

• Construction of road and rail infrastructurewhere the tunnel crosses consistent and well compacted soils.

In these cases, open shields allow for efficient excavation, with lower operating costs and shorter execution times. However, detailed geotechnical studies are essential to evaluate the feasibility of this technique for each specific project.

Eurohinca application example

Eurohinca has implemented open tunnel shields in various microtunneling projects, especially in urban infrastructure crossings and in the installation of supply and sewage pipes. These techniques have allowed the development of efficient solutions with minimum impact on the surface and optimization of resources.

Closed tunnel shields: Characteristics and applications

The closed tunnel shieldsalso known as tunnel boring machines with face pressurization, use a containment system to stabilize the ground during excavation. This can be by means of sludge pressure (EPB - Earth Pressure Balance) or carrier liquids such as bentonite (Slurry Shield). These systems are essential in projects where the soil presents high risks of instability.

When is its use recommended?

Closed tunnel shields are recommended in scenarios where greater control over the terrain and water table is required. Some of their applications include:

• Excavations in granular, sandy or heterogeneous soilswhere the stability of the excavation face is more difficult to maintain.

• Conditions with high water tablewhere it is necessary to avoid water infiltration to ensure the safety of the excavation.

• Construction of large diameter tunnelssuch as subway systems or large sewer mains, where ground pressure and water require specialized containment.

• Works in dense urban environments where a strict settlement control and minimal damage to nearby buildings.

The use of closed shields ensures that excavation can be performed without risk of collapse, even in challenging terrain. However, their implementation requires more planning and higher operating costs due to the need for advanced containment systems.

Eurohinca application example

Eurohinca has used closed shields on the construction of submarine outfalls, guaranteeing the stability of the tunnel in marine conditions and low cohesion soils. Thanks to this technology, it has been possible to minimize the environmental impact and guarantee the structural safety of outfalls in various coastal areas.

Key differences between the two types of shields

Open and closed shields have different applications and benefits, and their selection depends entirely on soil characteristics and project objectives. While open shields are more suitable for compact and stable soils, closed shields are used in loose and water bearing soils.

One of the most important factors to consider is the safety of personnel and the stability of the excavation face. In projects where the risk of collapse is high, closed shields represent a reliable solution, although with higher costs and execution times. On the other hand, open shields can be faster and more economical in suitable terrain.

Considerations for choosing the appropriate method

To determine which type of shield is most suitable for a tunneling project, several key factors must be analyzed:

• Geology and soil compositionEvaluate whether the soil is cohesive, granular or heterogeneous.

• Presence and control of groundwaterIdentify whether a high water table exists and what control measures are required.

• Tunnel size and purposeConsider the diameter of the tunnel and whether it will be used for sanitation, transportation or drainage.

• Project environmentDetermine whether the construction is in an urban area with sensitive infrastructure or in an area with low building density.

Based on these criteria, the engineers at Eurohinca select the best option for each project, guaranteeing the efficiency and safety of the construction process.

To learn more about our tunneling solutions and trenchless technologies, visit our section on projects.