Steel Pipe Jacking in Yangzhou Water Plant Turbid Water Pipeline Project

Literature Overview

This paper published in China Water Affairs (2014, Vol. 30, No. 10, pp. 100–102) by Zheng Quanxing, Yue Bing, and Xu Yingwu from Yangzhou Water Company and Shanghai Foundation Engineering Group, documents the practical application of pipe jacking technology for a DN2000 turbid water pipeline crossing the Beijing-Hangzhou Grand Canal at Yangzhou's first water treatment plant. The project involved substantial jacking distances, challenging geological conditions, and complex surrounding environments, making it an instructive case study for engineers involved in large-diameter pipeline jacking operations.

Core Technical Content

Project Background and Challenges

The DN2000 turbid water pipeline required to cross the Beijing-Hangzhou Grand Canal, one of China's most important waterways. The project faced several distinctive challenges:

Large diameter: DN2000 represents a significantly larger jacking diameter than typical municipal pipelines, requiring greater jacking forces and more robust equipment.
Special geological conditions: The strata encountered required careful analysis to determine appropriate excavation methods and support systems.
Complex surroundings: Proximity to the Grand Canal and urban infrastructure imposed strict deformation and settlement control requirements.
Substantial jacking volume: The total jacking distance and number of pipe segments created cumulative friction and alignment challenges.

Key Technical Measures

The paper details several critical technical measures that ensured successful project execution:

Technical Measure	Purpose	Implementation Detail
Intermediate jacking stations	Reduce cumulative friction force	Strategically placed along the jacking route to break the jacking force into manageable segments
Tool head breakout	Ensure controlled and safe exit from shaft	Careful ground improvement and gradual breakout to prevent ground collapse
Pipe welding	Achieve structural integrity of the jacked pipeline	Field welding of pipe segments with strict quality control
Grouting and friction reduction	Minimize jacking resistance	Synchronous grouting behind the tool head to reduce skin friction
Tool head entry into receiving shaft	Controlled and damage-free entry	Precise alignment and gradual entry to prevent pipe damage or misalignment

Intermediate Jacking Station Design

The most technically significant aspect of this project was the design and implementation of intermediate jacking stations. For a DN2000 pipe, the cumulative friction force over a long jacking distance can exceed the capacity of a single jacking station. The intermediate stations effectively divide the jacking force into segments, with each station bearing only the friction force for the pipe length between it and the next station.

Key design considerations for intermediate jacking stations include:

Foundation capacity: The station must resist the full jacking reaction force without excessive settlement.
Structural integrity: The reaction wall must be designed to withstand repeated loading cycles.
Accessibility: Equipment must be able to enter and exit the station for maintenance and operation.
Waterproofing: In underground conditions, the station must be watertight to prevent water ingress.

Pipe Welding in Jacking Operations

The field welding of DN2000 pipe segments is a critical quality control point. The paper emphasizes that the welding must achieve:

Full penetration and fusion to ensure structural continuity.
Acceptable residual stress levels to prevent distortion during jacking.
Proper alignment to minimize eccentric loading on the jacking system.

For large-diameter pipes, the welding procedure typically involves:

Pre-fit and alignment of pipe ends with precise gap control.
Root pass welding using GTAW (TIG) for full penetration.
Fill passes using SMAW or FCAW.
Cap pass welding with proper profile finishing.
Non-destructive testing (RT or UT) of critical welds.

Engineering Practice Implications

This case study provides valuable lessons for engineers planning large-diameter pipe jacking projects:

Friction force estimation must be conservative, and intermediate jacking stations should be designed with adequate safety margins.
Grouting strategy is not merely a support measure but a critical friction reduction technique that directly affects the required jacking force.
Welding quality in jacked pipelines is particularly important because the pipe is subjected to compressive axial loads during jacking and subsequent service loads.
Tool head control during breakout and entry operations requires careful planning to avoid ground collapse, pipe damage, or misalignment.

Key Questions and Reflections

One question that arises from this case study is the long-term performance of the welded joints under sustained compressive loading. While the initial welding quality may be satisfactory, the cyclic loading during jacking and the sustained service loads could potentially affect the weld integrity over time. Additionally, the paper's emphasis on construction measures rather than detailed material or welding procedure specifications suggests that the project relied heavily on experienced workmanship, which raises questions about reproducibility and standardization.

Summary

The Yangzhou water plant pipe jacking project demonstrates the successful application of large-diameter pipe jacking technology under challenging conditions, with intermediate jacking stations, controlled breakout and entry procedures, field pipe welding, and grouting-based friction reduction as the key technical pillars. The case study underscores that large-diameter jacking operations require careful integration of geotechnical analysis, structural design, welding quality control, and construction management to achieve successful outcomes in complex environments.