Influence of Construction Sequence on Deformation of Existing Foundations Reinforced by Micro Steel Pipe Piles

Literature Overview

This study by Liu Jiangtao and colleagues, published in 2024 in the Journal of Civil and Environmental Engineering (Vol. 46, No. 4, pp. 100–108), investigates how different micro steel pipe pile driving sequences affect the deformation characteristics of existing foundations during reinforcement operations. The research was funded by the National Natural Science Foundation of China (Grant No. 52027812) and was conducted jointly by China Railway (Shanghai) Investment Group Co., Ltd. and the Key Laboratory of Geotechnical and Coastal Disaster Reduction of Hohai University. The work addresses a significant practical gap in the field of foundation reinforcement, where construction sequencing decisions are often made empirically rather than through systematic investigation.

Core Research Methodology

The researchers employed a transparent soil model test approach combined with Particle Image Velocimetry (PIV) processing technology to visualize soil displacement fields during pile driving operations. This combination allows for direct observation of internal soil deformation, which is extremely difficult to capture in field conditions. Four different pile driving sequences were investigated: counter-clockwise, combined clockwise-counter-clockwise, Z-shaped, and symmetric arrangements. The transparent soil material simulates the mechanical behavior of real soil while permitting optical measurement of internal displacements.

The experimental setup involved constructing scale model foundations with pile caps and driving micro steel pipe piles around and beneath these foundations under controlled conditions. The PIV system captured full-field displacement data, enabling quantitative analysis of soil movement patterns and their propagation to the existing foundation structure.

Key Technical Findings

The study reveals that piles driven beneath the pile cap exert a compaction effect on the surrounding soil, which is a critical observation for understanding ground disturbance during micro pile installation. When piles are driven near the perimeter of the pile cap, the displacement of soil beneath the cap is relatively small compared to conditions without a cap, indicating that the pile cap acts as a partial shield against soil disturbance propagation.

The symmetric driving sequence proved to be the optimal approach among the four tested methods. Under this sequence, the uplift displacement of the existing foundation was only 56% of that observed under the most unfavorable construction sequence. This finding has direct implications for engineering practice, where construction sequencing can be optimized to minimize adverse effects on existing structures.

Engineering Practice Integration

Micro steel pipe piles are widely used in building retrofitting, foundation reinforcement, and structural correction projects due to their high construction efficiency and minimal environmental impact. However, the sensitivity of existing foundations to construction sequencing means that improper sequencing can lead to unacceptable displacements, tilting, or even structural damage. The research findings provide a quantitative basis for selecting optimal driving sequences in practice.

From a practical standpoint, engineers should consider the following when planning micro pile reinforcement projects:

• Assess the geometry and load-bearing capacity of the existing pile cap before determining the driving sequence.
• Prefer symmetric driving sequences to minimize differential settlement and uplift of the existing foundation.
• Account for the compaction effect of piles driven beneath pile caps on surrounding soil, particularly in soft ground conditions where additional settlement may be triggered.
• Use the quantitative reduction factors reported in this study (42% influence range reduction and 36% maximum displacement reduction) as preliminary estimates for impact assessment during project planning phases.

Key Questions and Reflections

This study raises several important questions for further investigation. First, the model test conditions are necessarily simplified compared to real field conditions, and the transferability of results to full-scale projects requires careful consideration of scale effects. Second, the study focuses on displacement fields but does not extensively address the long-term stability of the reinforced foundation system. Third, the interaction between micro pile driving and adjacent underground utilities or neighboring structures is not covered, which is a common concern in urban construction environments.

The use of transparent soil and PIV technology represents a methodological advancement that could be further developed for other geotechnical applications. The ability to visualize internal soil behavior provides insights that are simply unattainable through conventional field monitoring methods alone.

Study Insights and Implications

The most significant insight from this research is the quantitative demonstration that construction sequencing is not merely a procedural preference but a critical technical variable that directly affects the safety and performance of foundation reinforcement operations. The finding that symmetric sequencing reduces uplift displacement to 56% of the worst-case scenario provides a compelling argument for systematic planning of pile driving operations. Engineers working on foundation retrofitting projects should incorporate sequencing optimization into their design and construction planning, rather than treating it as a secondary consideration. This study contributes meaningfully to the evidence base for rational construction sequencing in foundation reinforcement practice.