Use of Rubber Airbags in TBM Breakout and Ground Pressure Sealing

Industry Knowledge

In tunnel construction projects using Tunnel Boring Machines (TBMs), one of the most critical and technically demanding stages is the breakout process, when the TBM exits the soil or rock strata into a shaft or working chamber.

During this stage, controlling ground pressure and preventing soil or water intrusion becomes a major engineering challenge. To address this issue, inflatable rubber airbags are widely used as a flexible pressure-blocking and sealing solution between the TBM and surrounding ground layers.

Engineering Background: Pressure Control During TBM Breakout

When a TBM approaches the exit point

Ground pressure remains active around the shield

Soil or water may rush into the working space

Rigid structures alone cannot fully adapt to irregular gaps

Excessive stress may damage sealing systems or structural components

Therefore, a flexible and controllable sealing medium is required to temporarily block ground pressure and stabilize the breakout area.

Installation Position of the Airbag

In practical engineering applications, the rubber airbag is:

Installed between the TBM shield and the surrounding ground layer

Positioned at the breakout interface, where the TBM exits the tunnel

Located between the shield structure and rubber sealing plates or surrounding soil

This placement allows the airbag to act directly against ground pressure while maintaining controlled deformation.

Main Function: Ground Pressure Blocking and Sealing

The primary role of the airbag is to:

Block pressure from the surrounding soil or rock layers

Act as a temporary sealing structure

Prevent sudden inflow of soil, water, or slurry

Stabilize the working environment during TBM breakout

In engineering terms, the airbag functions as a flexible pressure barrier, similar to a deformable seal.

Working Principle of the Airbag

During operation:

The airbag is installed in its designated position before breakout

Inflation begins gradually, typically starting at around 0.01 MPa

Once internal pressure is applied, the airbag quickly becomes firm and load-bearing

The airbag expands to fill irregular gaps between the TBM and ground

Ground pressure is evenly resisted and redistributed through the airbag surface

Unlike rigid components, the airbag adapts to uneven surfaces and maintains effective contact.

Advantages of Using Airbags in TBM Breakout

Compared with traditional rigid sealing methods, rubber airbags offer several advantages:

Flexible deformation under pressure

Uniform load distribution

Reduced risk of local stress concentration

Improved sealing performance in irregular spaces

Simple inflation control and on-site adjustment

These characteristics make airbags particularly suitable for complex geological conditions.

Typical Engineering Experience

In multiple shield tunneling projects, airbags have been successfully used to:

Assist sealing during TBM breakout

Support rubber sealing plates by providing upward force

Stabilize the interface between the TBM and ground layers

Enhance overall safety during critical construction stages

Their performance has proven reliable under real construction conditions.

Conclusion

In TBM tunneling projects, especially during breakout operations, rubber airbags play a vital role as a flexible sealing and pressure-blocking solution.
Installed between the TBM and surrounding strata, they effectively resist ground pressure and improve construction safety.

As tunneling projects continue to increase in scale and complexity, customized rubber airbags designed for breakout sealing will remain an important auxiliary component in modern TBM engineering.