Non-Excavation Construction Method:
1. Directional Pipe Method Construction Process
The construction process of the directional pipe method includes: geological survey, crossing curve design, measuring magnetic azimuth, drilling position setup, drilling the guide hole, reaming, backtracking, environmental protection, and landform restoration. This method ensures minimal disruption to the surface while effectively installing underground pipelines.
2. Working Principle of the Guiding Pipe Method
The horizontal directional drilling rig operates by following a pre-designed curved trajectory from the surface. A drill bit is used to create an approximately horizontal guide hole, after which the diameter is increased using a reamer. The working pipe, which has a smaller diameter than the reamer, is pulled back through the borehole during the reverse reaming process. In this project, graded reaming was applied in two stages to ensure smooth pipeline installation.
3. Equipment Setup, Installation, and Commissioning
Before placing the drilling rig, the site (20m × 30m) must be leveled to allow for equipment movement and access. The storage area for materials should not exceed 15cm above ground level and must be compacted with a side ditch of at least 0.3m × 0.3m. Once the site axis is determined, the rig is placed accurately based on the site conditions and angle. After installation of the drilling, mud, and solid control equipment, all systems are tested to ensure safe operation. The steering device is also calibrated for precision. Mud pits (2m × 4m × 2m and 2m × 3m × 2m) are dug at both ends for waste collection, and excess mud is transported via suction trucks.
4. Drilling the Guide Hole
The crossing section is assumed to have Type II soil conditions. The guide hole trajectory is designed based on ground conditions. Preventing landslides is crucial during this phase. A suitable mud ratio is formulated according to the geological structure, with macromolecular polymers and multifunctional agents added to increase viscosity and reduce water loss. The mud density is maintained between 1.02–1.05 g/cm³, with a viscosity of 45–55 seconds and a water loss of 10 mL. Lubricants are added in inclined sections to reduce friction and prevent sticking. The guide hole is drilled strictly along the design curve, with the steering system using a cable-based approach for accuracy. Pre-reaming follows once the pilot hole is completed.
5. Pre-Reaming and Hole Expansion
a. The guide hole is expanded using an FDP-30 directional drilling machine, with gradual reaming levels based on rotating and pulling pressures.
b. Reaming is performed using a φ320mm spiral reamer and a φ450mm spiral reamer.
c. Before reaming, the mud circulation system is prepared. The FDP-30 rig supports 5 m³/h of mud flow, with a maximum of 120 m³/day. Mud pits are dug at both ends, and specialized equipment is used for cleaning. This ensures a clean and organized construction site.
6. Pulling Back the Pipeline
a. A special returning device is used, combining rotation and pulling back with mud to protect the anti-corrosion layer.
b. The rotary transfer case is specially designed for stability.
c. Connections between the centralizer, working pipe, and puller must be secure and sealed.
d. High-viscosity mud with appropriate additives is used to reduce resistance and load on the rig.
e. Before pulling back the φ273×9 steel pipe, it’s essential to verify that sufficient mud is present in the hole to lubricate the wall.
f. After confirming the welding and anti-corrosion of the steel pipe, all towing systems are checked for optimal performance.
g. Rollers are placed every 20 meters to prevent damage to the steel pipe during dragging.
h. The pulling speed is controlled at 0.08 m/s, ensuring a smooth and uniform motion. Operators monitor back pressure and take necessary actions as needed.
i. Most of the mud is recycled, requiring temporary storage pits for purification.
7. Landform Restoration
After completing the pipeline installation, the site is cleaned, and all construction equipment is removed to restore the original topography.
The construction process is illustrated in Figure 1.
This project marks a milestone in Zhongshan City's history, being the largest gas pipeline project to cross a river using directional drilling and non-excavation techniques. It will provide residents and businesses north of the Shijie River with a safe, clean, and continuous supply of natural gas from Hong Kong, boosting the region's economic growth and improving living standards. It also lays the groundwork for future gas infrastructure.
3. Conclusion
Non-excavation technology offers numerous benefits, including reduced road excavation, lower costs, and the ability to install pipelines in areas where traditional methods are impractical. It is particularly useful in projects like the West-East Gas Transmission and large-scale LNG pipeline networks. As natural gas becomes a more widely used clean energy source, non-excavation methods play a key role in gas replacement projects and maintenance of existing pipelines. They also help ensure uninterrupted gas supply when installing zone valves and pipes. This technology not only advances gas construction methods but also reflects the rapid development of modern engineering practices.
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