Advanced Trenching Techniques for Diaphragm Wall Construction

Introduction

Trenching is the most critical process in diaphragm wall construction, often accounting for over half of the total construction time. Optimizing trenching operations is key to improving efficiency and ensuring quality. With increasing demands for productivity, new equipment and methods continue to evolve.

Primary Trenching Methods & Equipment

1. Grab Bucket Trenching Method

Grab bucket trenching machines have become the dominant equipment for diaphragm wall construction in China, with over 100 units in operation (mostly imported).

Types of Grab Buckets:

• Wire rope grab buckets

• Hydraulic guide wall grab buckets

• Kelly bar grab buckets

• Hybrid grab buckets

Operation Principle:

The bucket cuts soil with its teeth, collects the material, and lifts it out of the trench for disposal. This cycle repeats until the desired depth is achieved.

Applications:

Widely used in construction and subway projects in major cities like Beijing, Shanghai, Tianjin, and Guangzhou. Notable projects include:

• Beijing National Grand Theatre

• Shanghai Jinmao Tower

• Tianjin Hongji Building

• Nanjing Xinjiekou Metro Station

• Shanghai World Financial Center

Technical Specifications:

• Slot width: 3.8-7.2m

• Single grab width: ~2.4m (maximum bucket opening)

Advantages:

• Low noise and vibration

• High efficiency

• Advanced models feature real-time inclination monitoring (accuracy up to 1/300)

Limitations:

• Restricted in hard strata

• Requires complementary methods for complete operation

Major Manufacturers:

• Italy: Soilmec, Casagrande

• Germany: Bauer, Liebherr, Leffer, Wirth

• Japan: Masago

2. Impact Drilling Trenching Method

One of the earliest diaphragm wall construction methods, still valuable when combined with modern techniques.

Variants:

• Conventional impact drilling (drill-split method)

• Impact reverse circulation (drill-suction method)

Applications:

Effective in complex strata with boulders and hard rock. Used in:

• Yangtze River Three Gorges Project

• Runyang Yangtze River Bridge

• Record depth: 101m (Yele Hydropower Station, Sichuan)

Advantages:

• Simple equipment

• Low cost

• Excellent for hard formations

Disadvantages:

• Low efficiency

• Moderate quality

Equipment Models:

• YKC series

• CZ-22/30

• CJF/CIS series

3. Rotary Drilling Trenching Method

Vertical Shaft Rotary Drilling:

a) Single-axis: For pilot holes
b) Multi-axis: For trench excavation

Horizontal Shaft (Cutter Machines):

The most advanced trenching equipment with two rotating wheels.

Cutter Machine Advantages:

• Exceptional strata adaptability (including 200MPa rock)

• High efficiency (20-40m³/hr in sediment)

• Precision (1/1000-2/1000 verticality)

• Deep trench capability (up to 150m)

• Automated operation with real-time monitoring

Limitations:

• High equipment cost

• Sensitive to obstructions like boulders

Notable Projects:

• Three Gorges Project

• Shenzhen Metro

• Nanjing Zifeng Tower

• Shanghai World Expo 500kV Substation

Manufacturers:

• Germany: Bauer (BC series)

• France: HF series

• Italy: Casagrande (K3/HM)

• Japan: TBW, EM/EMX

Innovative Trenching Combinations

Hybrid Methods for Complex Strata:

1. Grab-Impact Combination:

   • Impact drills main holes

   • Grab clears between holes

   • Efficiency improvement: 1-3x

2. Drill-Grab Combination:

   • Pilot holes are drilled first

   • Grab removes intermediate material

3. Cutter-Based Combinations:

   • Grab-Cutter: Soft upper layers with a cutter for hard strata

   • Drill-Cutter: For varied geological conditions

   • Cutter-Impact: For extremely hard formations

Specialized Techniques:

• Milling Joints: Creates superior wall connections

• H-beam Joints: For structural continuity

Conclusion

As urban underground construction grows more complex, combining trenching methods delivers optimal results in efficiency, cost, and quality. Advanced cutter machines, despite higher initial costs, offer unparalleled performance in challenging conditions and are poised to become standard equipment for demanding projects.

The evolution from single-method approaches to integrated solutions reflects the industry’s response to increasingly difficult construction environments, ensuring diaphragm walls remain a reliable choice for deep excavations and foundation support.