I. Introduction: The Settlement Challenge in Tunnel Construction

One of the most significant challenges in building underground infrastructure and tunnels in urban environments is controlling the surface settlement caused by excavation. Any loosening and deformation of the surrounding ground will propagate upward, jeopardizing the safety of surface structures, utilities, and traffic routes.

Tunnel Pre-Support Systems, especially those based on the Pipe Umbrella System and other proactive measures, are the most effective technical means to actively control ground deformation and achieve Surface Settlement Control. They work by reinforcing the ground before the tunnel is excavated, keeping ground movement within acceptable limits.

II. Principle of Settlement Control by Pre-Support Systems

Pre-support systems (such as pipe umbrellas or pre-grouting) act by reinforcing and confining the ground before excavation, thereby reducing ground movement at the source and controlling surface subsidence.

A. Reduction of the Ground Loosening Zone (Ground Loss Reduction)

• Confinement: The stabilizing ring formed by Tunnel Roof Support Pipes or grout (e.g., the Pipe Umbrella System) exerts pre-confining pressure on the ground ahead of the tunnel face.

• Effect: This action effectively reduces the extent and depth of the loosened ground zone, consequently minimizing the volume of ground loss transferred to the surface. Reduced ground loss directly correlates with reduced surface settlement.

B. Enhancing Ground Self-Bearing Capacity

• Stiffness Enhancement: By using Forepoling Pipes in conjunction with grouting, the loose ground or rock mass is consolidated into a high-strength composite body, significantly increasing the ground's overall stiffness and load-bearing capacity.

• Timeliness: This "support first, then excavate" philosophy ensures that ground deformation is controlled in its earliest stages, preventing the large, delayed settlements typical of conventional excavation methods.

III. Key Pre-Support Methods and Settlement Contribution

Different pre-support systems are suited to different settlement control requirements, but all rely on high-quality Steel Casing Pipes as either support elements or injection conduits.

For detailed structural and design information on the pipe umbrella system, please refer to: 【Pipe-Design】 Pipe Umbrella System Design Principles and Applicable Conditions.

IV. Engineering Application and Monitoring for Settlement Control

In urban underground projects, settlement control often demands accuracy down to the millimeter level.

1. Tiered Control: Settlement control targets are set based on the sensitivity of surface buildings. Sensitive areas require more dense Tunnel Pre-Support and smaller excavation advances.

2. Real-Time Monitoring: High-precision, real-time monitoring of both surface and internal tunnel deformation is mandatory. The monitoring data guides adjustments to the excavation method, support timing, and support density.

3. Corrective Grouting: If monitoring reveals excessive settlement, Perforated Grouting Pipes (Sleeve Pipes) can be used for secondary injections, providing targeted consolidation of localized loosened zones for precise settlement remediation.

V. Conclusion: Pre-Support Systems Ensure Urban Safety

Underground Engineering Pre-Support Systems are core technologies for safe, efficient, and environmentally responsible tunnel construction. By precisely designing and implementing Tunnel Roof Support Pipes and Steel Casing Support methods, engineering teams effectively limit ground loosening, minimize the risk of surface settlement, and thus safeguard urban infrastructure and the surrounding environment.