Zhuojin Pipe Fitting Co., LtdApplication of Steel Pipe Static Pressure Pile Foundation Underpinning Reinforcement Technology
Literature Overview
This paper, authored by Zhang Tinghui, Li Xiaogang, and Ding Xiaoqiang from Shaanxi Tiandi Geology Co., Ltd., was published in Construction Technology (2016, Vol. 45, No. 16, pp. 53-56). The study addresses a critical geotechnical engineering challenge: foundation settlement and cracking caused by collapsible weak soil layers, using steel pipe static pressure piles as the underpinning solution. The case study focuses on a gas pump room and fan foundation at a coal mine in Shaanxi Province, where significant settlement deformation was observed due to the collapsible nature of the subgrade soil.
Core Technical Principles
The static pressure pile underpinning method operates on the principle of transferring structural loads from a failing foundation to deeper, more competent soil layers through driven steel pipe piles. Unlike conventional driven piles that rely on impact energy, static pressure piles are inserted using hydraulic jacking forces applied through the pile head, which minimizes vibration and disturbance to adjacent structures. This is particularly important when underpinning operational facilities such as gas pump rooms where continued operation must be maintained during construction.
The key technical parameters identified in the study include pile tip embedment depth, jacking force requirements, and construction process control. The authors emphasize that for collapsible soils, the pile must penetrate through the entire collapsible layer into competent bearing strata to achieve effective load transfer. The jacking force serves as both an installation parameter and an in-situ quality indicator, providing real-time feedback on soil resistance encountered during pile installation.
Construction Process and Quality Control
The construction methodology follows a systematic approach:
- Site survey and geological investigation to determine the thickness and properties of the collapsible layer.
- Design of pile layout, diameter, and required embedment depth based on structural load requirements.
- Pile insertion using hydraulic jacking equipment with continuous monitoring of jacking force.
- Pile head treatment and connection to the existing foundation structure.
- Load testing to verify underpinning effectiveness.
| Quality Control Parameter | Acceptance Criteria | Inspection Method |
|---|---|---|
| Pile tip embedment depth | Beyond collapsible layer into competent stratum | Downhole logging or measurement |
| Jacking force | Within design range (±15%) | Force gauge monitoring |
| Pile verticality | ≤1.0% of pile length | Plumb bob or inclinometer |
| Pile diameter and wall thickness | Per design specification | Dimensional measurement |
| Pile head connection | Full bond, no gaps | Visual and MT inspection |
The study highlights that process control during construction is more critical than post-construction testing for this application. The authors advocate for continuous monitoring of jacking force throughout pile installation, as variations in force profiles indicate changes in soil conditions and potential installation problems such as pile buckling or insufficient penetration.
Engineering Practice Insights
From a steel pipe perspective, the selection of pile material is critical. The study implicitly relies on standard steel pipe specifications, where the pipe must possess adequate yield strength, ductility, and corrosion resistance for long-term service in the ground. For coal mine environments with potential gas exposure, the steel pipe material grade and surface protection become additional design considerations. The pipe connection method at the pile head is equally important, as it must create a reliable load path between the existing structure and the new pile system.
The FMEA approach can be applied to identify potential failure modes in this system: inadequate pile penetration leading to continued settlement, insufficient connection strength causing load transfer failure, and corrosion of steel pipe reducing long-term capacity. Each of these failure modes requires specific preventive measures during design and construction phases.
Study Reflections
This paper demonstrates a practical and effective solution to a common geotechnical problem encountered in collapsible soil regions. The emphasis on process control during pile installation rather than relying solely on end-product testing reflects mature engineering practice. For steel pipe suppliers and fabricators involved in such projects, understanding the specific requirements for pile application—particularly regarding material properties, dimensional tolerances, and connection details—enables better product specification and quality assurance. The case study provides valuable reference data for similar applications in regions with collapsible loess soils.