TRD Construction Method Combined with High-Strength GZH Pipe Piles: A Cost-Effective Solution for Deep Foundation Excavation

Abstract

This innovative construction technique utilizes chainsaw-type cutters to horizontally excavate, trench, grout, and mix with in-situ soil to create cement-soil walls. By incorporating more economical GZH high-strength support pipe piles into the TRD uniform-thickness cement-soil walls, it achieves dual functionality as both retaining walls and water cutoff walls, significantly optimizing construction costs. This paper presents comprehensive research and practical applications of this technology, along with key conclusions and recommendations.

1. Introduction

With China’s rapid economic development, urban construction has witnessed unprecedented growth, leading to numerous high-rise buildings and a surge in deep foundation pit projects. However, traditional foundation pit support methods often fail to meet the demanding requirements of ultra-large, first-class deep foundation pits in terms of wall depth, uniformity, continuity, surface smoothness, thickness, wall stiffness, and water cutoff performance. To address these challenges and break through the technical bottlenecks in deep excavation construction, the adoption and continuous improvement of the TRD (Trench Cutting Re-mixing Deep Wall) method has become imperative.

2. Technical Characteristics and Principles

2.1 High Construction Precision

Through measures such as installing positioning frames and strictly controlling pile driving timing, this method ensures precise control over the verticality and elevation of GZH high-strength support pipe piles within the TRD cement-soil walls.

2.2 Cost Efficiency

Compared to traditional methods using H-beams, row piles with triple-axis cutoff walls, or underground continuous walls, the GZH pipe pile solution reduces steel consumption by 30-40%, significantly lowering project costs.

2.3 Enhanced Construction Stability

By driving GZH pipe piles 1-2 hours after wall formation, the method prevents quality issues caused by rapid pile sinking. Additionally, the cutter remains underground throughout the process, eliminating risk of equipment overturning.

2.4 Superior Wall Quality

The TRD method ensures uniform mixing, consistent wall thickness (typically 850mm), and high density, resulting in exceptional continuity and water cutoff performance (permeability coefficient ≤1×10⁻⁷ cm/s).

2.5 Wide Adaptability

Suitable for various applications including:

• Building foundation pit support and cutoff walls
• Foundation construction for structures and dams
• Landslide prevention for highway subgrades
  Compatible with diverse soil conditions (sand, silt, clay, gravel) and can penetrate soft, strongly weathered rock aquicludes with cutoff depths up to 53m.

2.6 Technical Principles

TRD Method:
Multi-section cutting boxes equipped with chainsaw cutters are inserted into the ground. As the cutters rotate and move horizontally, they inject cutting and solidifying fluids that mix with in-situ soil to form uniform-thickness continuous walls.

GZH Pipe Piles:
Specially designed for deep excavation support, these piles offer 40% higher bending moment resistance compared to standard PHC piles. Replacing traditional H-beams with GZH piles maintains structural strength while reducing steel usage by approximately 35%.

3. Construction Process and Key Operations

3.1 Construction Workflow

1. Site preparation → 2. Trench excavation & equipment positioning → 3. Soil cutting & grout mixing → 4. 1-2h curing & frame installation → 5. Pipe pile lifting → 6. Pile driving & verticality control → 7. Final driving & elevation control

3.2 Key Operational Points

3.2.1 Site Preparation

• Level the construction area and build temporary access roads
• Treat soft ground conditions (drainage, dredging, backfilling)
• Conduct precise surveying with ≤5mm positioning error

3.2.2 Trench Excavation

• Excavate along the wall alignment using excavators
• Compact the working area with 5 passes of tracked machinery
• Lay steel plates (20mm thick) to distribute equipment loads

3.2.3 Wall Construction

• Create starter pits (3m deep × 2m long × 1m wide)
• Inject cutting fluid (bentonite slurry) during initial penetration
• Achieve design depth (typically 30-60m) with verticality ≤1/250
• Implement real-time monitoring via inclinometers in cutting boxes

3.2.4 Pile Installation

• Use specialized positioning frames with 40 cm-spaced guide holes
• Employ the three-point lifting method for GZH piles (800-1000mm diameter)
• Control verticality within 0.5% using dual-axis theodolites
• Implement staged driving:
  • Phase 1: Self-weight sinking (first 1 hour)
  • Phase 2: Assisted driving (30-50cm/hammer blow)

4. Case Study: Nanjing Straits City Project

Project Parameters:

• Location: Plot E, Phase 1 Residential Community Center
• Wall depth: 53m
• Total length: 200 linear meters
• Wall thickness: 850mm
• GZH pile specification: Φ800mm × 25m

Performance Metrics:

• Construction speed: 8-12m/day
• Vertical accuracy: 1/300
• Cost savings: 28% vs. diaphragm wall method

5. Advantages and Conclusions

Key Benefits:

1. Economic Efficiency
   • 25-35% cost reduction compared to traditional methods
   • 40% less steel consumption than H-beam solutions
2. Construction Speed
   • 30% faster than SMW (Soil Mixing Wall) methods
   • Simultaneous wall formation and pile installation
3. Environmental Advantages
   • Zero vibration pollution
   • 60% less spoil generation vs. secant pile walls
   • Reusable positioning systems
4. Quality Assurance
   • Uniform wall thickness (±2cm tolerance)
   • Seamless joints (leakage <0.1L/m²/day)

This innovative combination of TRD and GZH technologies represents a significant advancement in deep excavation support, particularly suitable for urban projects with strict environmental requirements and complex geological conditions. Future development should focus on automated monitoring systems and hybrid solutions combining this method with jet grouting for ultra-deep applications (>60m).