Zhuojin Pipe Fitting Co., LtdEffect of Steel Pipe Concrete Column Positioning Deviation on Underground Structure Displacement
Literature Overview
This 2013 paper by Wang Ke, Li Shunqun, and Yin Changquan, published in the Journal of Guangxi University (Natural Science Edition), investigates the influence of steel pipe concrete column-pile positioning deviations on underground structure displacement in a cover-excavation inverted construction method subway station project in Tianjin. Using Midas/GTS three-dimensional construction process simulation, the study analyzes three different positioning deviation scenarios and their effects on column, pile, diaphragm wall, and floor slab displacements.
Technical Framework
The cover-excavation inverted construction method (also known as cut-and-cover with inverted construction sequence) involves constructing the roof slab first, then excavating beneath it while constructing lower structural elements. Steel pipe concrete columns serve as temporary and permanent support elements, and their positioning accuracy directly affects structural performance.
Construction Process Modeling
The Midas/GTS simulation captures the sequential construction stages:
- Stage 1: Diaphragm wall construction and ground anchor installation
- Stage 2: Roof slab construction with embedded steel pipe concrete columns
- Stage 3: Sequential excavation and floor slab construction (inverted sequence)
- Stage 4: Backfill and completion
The positioning deviation scenarios examined include:
| Deviation Type | Description | Magnitude Considered |
|---|---|---|
| Type A | Deviation perpendicular to track axis | 50, 100, 150 mm |
| Type B | Deviation parallel to track axis | 50, 100, 150 mm |
| Type C | Combined planar deviation | 50, 100, 150 mm |
Displacement Response Analysis
The study reveals important patterns in displacement behavior:
| Structure Element | Effect of Deviation on Horizontal Displacement (⊥ to track) | Effect on Vertical Displacement |
|---|---|---|
| Steel pipe concrete column | Increases with deviation magnitude | Slight decrease |
| Pile foundation | Increases with deviation magnitude | Minimal change |
| Diaphragm wall | Increases with deviation magnitude | Slight decrease |
| Floor slab | Moderate increase | Negligible change |
The key finding is that positioning deviation perpendicular to the track axis has a more pronounced effect on horizontal displacements than deviation parallel to the track axis. This anisotropic response is attributed to the asymmetric boundary conditions created by the subway station geometry relative to the excavation boundaries.
Engineering Practice Implications
Positioning Tolerance Standards
Based on the study's findings, positioning tolerance requirements for steel pipe concrete columns in inverted construction should consider:
| Tolerance Category | Recommended Limit | Basis |
|---|---|---|
| Plan position deviation | ≤100 mm | Acceptable displacement increase <10% |
| Vertical alignment | ≤50 mm | Minimal effect on vertical displacement |
| Column inclination | ≤1:300 | Prevents eccentric loading effects |
Construction Control Measures
For steel pipe concrete columns in inverted construction, the following construction control measures are recommended:
- Survey control: Establish high-precision control points with accuracy ≤±5 mm
- Guide tube method: Use steel guide tubes for pile/column positioning with inner diameter tolerance ±20 mm
- Real-time monitoring: Implement inclinometer and displacement monitoring during excavation stages
- Compensation design: Design connection details with sufficient flexibility to accommodate minor deviations
Materials and Welding Considerations
Steel pipe concrete columns used in underground construction typically employ seamless steel pipes (GB/T 8162) or welded steel pipes (GB/T 8163) with wall thicknesses of 8-16 mm. The welding connections between steel pipes and embedded steel reinforcement require careful attention to:
- Pre-weld preparation: Ensure clean, deburred pipe ends with proper fit-up gap (2-4 mm)
- Welding process selection: GTAW (gas tungsten arc welding) for root pass, SMAW or FCAW for fill and cap passes
- Weld quality requirements: 100% ultrasonic testing per GB/T 11345, no level II or higher indications
- Post-weld treatment: Stress relief for critical connections in thick-walled pipes (>12 mm)
Summary and Study Insights
This research provides valuable quantitative data on the sensitivity of underground structure performance to steel pipe concrete column positioning deviations. The finding that perpendicular deviations have greater impact than parallel deviations offers practical guidance for prioritizing survey accuracy in different directions. For steel pipe contractors and construction engineers, the study reinforces the importance of precise positioning control and suggests that deviations exceeding 100 mm may require design review or compensatory measures. The research methodology using construction process simulation represents a modern approach to construction engineering that can be extended to other complex underground construction scenarios.