Grout holes in precast jacking pipes serve multiple purposes throughout the pipe jacking process:
Lubricant Injection: These holes facilitate the injection of bentonite or other lubricants, crucial for reducing frictional resistance between the pipes and surrounding soil. In cohesive soils, the lubricant creates a barrier that prevents soil particles from adhering to the pipe, ensuring the shearing plane remains within the lubricant itself, as outlined by R. N. Craig (1983). For granular soils, the lubricant mixes with the soil, significantly decreasing friction. This lubrication enables the jacking of longer pipe lengths without the need for intermediate jacking stations, enhancing the efficiency of the process.
Post-Jacking Grouting: After completing pipe jacking, the grout holes become access points for subsequent grouting operations. Grout is injected through these holes to fill the annular space between the pipes and surrounding soil completely. This grouting process stabilizes the pipeline, prevents soil settlement, and protects the pipe from external forces.
Lifting Holes: During the initial placement of precast jacking pipes onto rails within the jacking pits, the grout holes also function as lifting points. This simplifies the handling and positioning of the pipes, ensuring a smooth and accurate installation process.
In summary, the strategic placement of grout holes in precast jacking pipes is a multifaceted design element. These holes enable efficient lubrication, facilitate post-jacking grouting, and assist in the initial pipe placement, collectively contributing to the successful and smooth execution of pipe jacking projects.