I. Introduction: Grouting as the Backbone of Modern Tunneling

Modern tunneling methodologies, such as Tunnel Boring Machines (TBMs) and Pipe Jacking (or micro-tunneling), rely heavily on precise ground treatment and void management. In these projects, the Tunnel Grouting Pipe and Pre-Injection Pipe are indispensable tools, serving two critical functions: stabilization ahead of the face and filling voids behind the lining.

The proper selection and use of these pipes ensure the stability of the tunnel face, mitigate water inflow, and prevent surface settlement—all vital for project success in dense urban environments or challenging geological conditions.

II. The Role of Pre-Injection Pipes for Face Stabilization

Pre-Injection Pipes are dedicated tools used for ground treatment ahead of the excavation face. This process is crucial in soft soils, fractured rock, or areas with high hydrostatic pressure.

A. Objectives of Pre-Injection

1. Water Control: Injecting grout through Pre-Injection Pipes creates a waterproof barrier, reducing water inflow and minimizing dewatering needs.

2. Ground Consolidation: Stabilizing loose soil or highly fractured rock masses, which increases the ground's cohesion and reduces the risk of collapse or large deformations during excavation.

3. Pressure Balance: In TBM operations, pre-grouting can help equalize pressure and prevent uncontrolled ground loss at the tunnel face.

B. Installation in Tunneling

These pipes, often high-pressure Steel Grouting Pipes, are drilled and installed in a fan-like pattern (known as "forepoling") around the perimeter of the tunnel profile, extending several meters ahead of the cutting face.

For detailed information on the various types of pipes that allow for controlled injection, see our main guide: 【 Pillar-Grouting】 Grouting Pipes: A Comprehensive Guide to Grouting Techniques, Perforated Pipe Selection, and Applications.

III. Tunnel Grouting Pipes in TBM and Pipe Jacking Projects

After excavation, Tunnel Grouting Pipes are essential for injecting grout into the annular void created by the TBM or the pipe jacking process.

A. Annular Gap Grouting (Synchro-Grouting)

When a TBM installs segments or a pipe jacking machine pushes a pipe, an annular space exists between the tunnel lining (or pipe) and the surrounding soil.

• Function: Tunnel Grouting Pipes (often permanently embedded in the lining segments) are used to quickly inject a specialized, fast-setting grout into this gap.

• Purpose:

1. Immediate Load Transfer: Ensures the lining segments are immediately supported by the surrounding ground.

2. Settlement Control: Fills the void, preventing the ground from relaxing and causing surface settlement.

3. Waterproofing: Provides an additional, permanent seal against groundwater ingress.

B. Lubrication Grouting in Pipe Jacking

In long-distance Pipe Jacking projects, a smooth pushing operation is critical. Specialized Grouting Pipes are used to inject a lubricating slurry (bentonite or polymer-based) along the exterior of the pipe string.

• Objective: To reduce friction and thrust forces needed to push the pipe string, which is a key technical challenge in long pipe-jacking drives.

IV. Material Selection: Steel Grouting Pipe Requirements

Due to the high pressures involved in TBM annular grouting and the potential for difficult ground conditions during pre-injection, Steel Grouting Pipe is the preferred choice for most permanent and critical tunnel grouting pipe installations.

• Pressure Resistance: Steel maintains its integrity under the high pumping pressures required to ensure the grout travels long distances and fills the entire annular void.

• Durability: Steel pipes are less susceptible to damage during the aggressive installation and pushing processes inherent in tunneling.

V. Conclusion: Precision Delivery for Subsurface Integrity

Tunnel Grouting Pipes and Pre-Injection Pipes are non-negotiable elements in safe and efficient underground construction. By utilizing the correct pipe type—from robust steel grouting pipe for deep pressure injection to specialized pipes for annular gap filling—engineers successfully achieve ground stabilization, minimize risk, and deliver high-quality infrastructure.