Non-excavation Construction Method:
1. Directional Pipe Method Construction Process
Geological Survey → Crossing Curve Design → Measuring Magnetic Azimuth → Drilling Position → Drilling Guide Hole → Reaming → Returning → Environmental Protection → Landform Restoration
2. Working Principle of the Guiding Pipe Method
The horizontal directional drilling rig operates by following a pre-designed curved trajectory from the surface to drill an approximately horizontal guide hole. Once the guide hole is completed, a larger reamer is used to enlarge the borehole. The working pipe, which has a smaller diameter than the reamer, is then pulled back through the borehole during the reaming process. This method ensures minimal disruption to the surrounding environment. In this project, graded reaming was applied in two stages, allowing for a more controlled and efficient installation of the pipeline.
3. Equipment Setup, Installation, and Commissioning
Before placing the drilling rig, the construction site (20m × 30m) was leveled to ensure smooth equipment movement and access. The storage area for materials was kept no more than 15cm above ground level, compacted, and equipped with side ditches of at least 0.3m × 0.3m. After marking the axis, the rig was positioned accurately based on the site conditions and angle. All equipment—drilling rigs, mud systems, and solid control devices—was installed, tested, and checked for safe operation. The steering device was also calibrated to ensure precision in the guide hole. Two mud pits were excavated—one measuring 2m × 4m × 2m at the entry point and another 2m × 3m × 2m at the exit. Excess mud was collected and transported using suction trucks.
4. Drilling the Guide Hole
The geological conditions of the crossing section were assumed to be Type II soil, and the guide hole trajectory was designed accordingly. Preventing landslides was a critical concern, so a suitable mud ratio was formulated based on the soil structure. Different mud formulas were used depending on the geological conditions. To enhance mud performance, macromolecular polymers and multifunctional agents were added to increase viscosity and reduce water loss, maintaining a density between 1.02–1.05 g/cm³, a viscosity of 45–55 seconds, and a water loss of 10 mL. A lubricant was also added to the mud in inclined sections to reduce friction and prevent the drill from sticking.
To ensure smooth pre-reaming and back-drag operations, the guide hole was drilled strictly along the design curve. After verifying the alignment and positioning the rig correctly, the pilot drill bit was connected to the drill pipe and tested for signal transmission. Once the drill reached 2 meters, it followed the designed trajectory. A cable steering system was used to improve accuracy. After completing the pilot hole, pre-reaming was carried out.
5. Pre-reaming and Hole Expansion
a. The pre-reaming was performed using an FDP-30 directional drilling rig, with mud being circulated while expanding the hole. The reaming level was gradually increased based on rotating and pulling pressures.
b. The number of reaming steps depended on the rig's torque and back pressure. The reaming levels included:
- Using a φ320mm spiral reamer for one pass.
- Using a φ450mm spiral reamer for another pass.
c. Before reaming, the mud circulation system was prepared. The FDP-30 rig supported a flow rate of 5 m³/hour, and the mud pump could handle up to 120 m³/day. Mud pits were dug at both the entrance and exit points, and special equipment was used to clean the mud. This ensured a clean and organized construction site.
6. Towing the Pipe
a. A specialized return device was used for towing the pipe, combined with rotation and mud injection to protect the anti-corrosion layer.
b. The rotary transfer case had a unique structure for enhanced performance.
c. Connections between the centralizer and the working pipe, as well as between the working pipe and the puller, were made secure, safe, and sealed.
d. High-viscosity, low-weight mud was used, along with appropriate additives and lubricants tailored to the geological conditions, to reduce drag resistance and ease the load on the drilling machine.
e. Before pulling back the φ273×9 steel pipe, it was verified that sufficient mud was present in the hole to lubricate the walls.
f. After confirming the welding and anti-corrosion of the steel pipe, it was connected to the tractor and the human end, and all towing systems were checked for optimal condition.
g. Before pulling, rollers were placed every 20 meters along the pipe to prevent damage from dragging, and a crane was used to assist.
h. During the pulling process, a steady speed of 0.08 m/s was maintained, avoiding any stops. Operators monitored back pressure changes and took timely action to ensure a smooth return.
i. Most of the mud was recycled, and temporary pits were dug for storage and purification.
7. Landform Restoration
After the pipeline work was complete, the site was cleaned, and all equipment was removed, restoring the original topography.
The construction process is illustrated in Figure 1.
The successful completion of this project marks a historic milestone for Zhongshan City, as it is the largest gas pipeline project ever undertaken, involving river crossing via directional drilling and non-excavation techniques. This will provide residents and businesses north of the Shijie River with a continuous, safe, and clean supply of natural gas from Hong Kong, promoting economic growth and improving living standards. It also lays the foundation for future natural gas infrastructure in the region.
3. Conclusion
Non-excavation technology not only minimizes road disruption and reduces costs but also overcomes challenges that traditional excavation methods cannot address, especially when repairing complex or difficult-to-access pipelines. This method is widely used in large-scale projects such as the West-East Gas Transmission and Guangdong LNG pipeline networks. With the increasing adoption of natural gas as a clean energy source, non-excavation techniques are essential for gas replacement projects, ensuring uninterrupted supply and enabling efficient pipeline upgrades. By replacing traditional trenching methods, this technology advances gas construction practices and reflects the rapid development of modern engineering and technological innovation.
Bazhou Lutong Engineering Co., Ltd.: http://
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