Introduction to Diaphragm Wall Construction
Diaphragm walls are critical components in construction, particularly for underground structures, providing support for excavation sites and ensuring stability. Their application is widespread in projects such as subways, dams, and high-rise buildings, where deep excavation is required. Below, we explore the advantages, disadvantages, and the detailed process involved in diaphragm wall construction.
Advantages and Disadvantages of Diaphragm Wall Construction
Advantages:
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High Stiffness and Integrity
Diaphragm walls offer excellent rigidity, ensuring the structural integrity of the excavation site during construction. -
Versatility Across Geological Conditions
These walls are adaptable to various soil and geological conditions, making them suitable for complex sites. -
Reduced Environmental Impact
The construction process for diaphragm walls minimizes environmental disruption, particularly in terms of noise and vibration. -
Faster Construction with Lower Costs
Reverse construction methods allow for quicker completion and reduced project costs.
Disadvantages:
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Mud Waste Management
Handling slurry waste can increase project costs. Improper slurry treatment or disposal may also result in environmental pollution. -
Wall Instability
The potential for wall collapse is a concern, particularly in unstable ground conditions or during improper construction methods. -
High Cost for Temporary Walls
When used as temporary barriers, diaphragm walls can be expensive, making them less cost-effective for short-term uses.
Diaphragm Wall Types and Structure
Diaphragm walls are classified based on their structural and load-bearing characteristics. These include:
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Temporary Walls
These are used for short-term support during construction, offering flexibility in their application. -
Reinforced Concrete Wall Panels
These include cast-in-place steel-reinforced concrete walls, varying in thickness depending on geological conditions, excavation depth, and equipment. Typical thicknesses range from 1000 mm to 3000 mm. -
Prefabricated Reinforced Concrete Walls
These walls are prefabricated and installed, offering efficiency and speed in construction.
Diaphragm Wall Construction Sequence
The process of diaphragm wall construction involves several stages to ensure precision and stability. These include:
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Guide Wall Construction
The purpose of the guide wall is to control construction precision and prevent soil movement during excavation. It is typically made of reinforced concrete or steel. -
Mud Wall Protection
Slurry is used to stabilize the excavation pit, support the soil structure, and reduce friction during drilling. Bentonite slurry is most commonly used for this purpose. -
Excavation and Slotting
Excavation is performed with precision, ensuring vertical alignment and accuracy. Slot lengths depend on factors such as geological conditions and equipment capabilities. -
Reinforcement Installation
Steel reinforcement cages are fabricated and placed into the slot, ensuring the wall’s strength and stability. -
Concrete Pouring
After placing the steel reinforcement, concrete is poured into the slot using specialized equipment, ensuring consistency and structural integrity.
Detailed Construction Process
Guide Wall Construction:
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Purpose and Function
The guide wall helps maintain excavation accuracy and serves as a support for the equipment. It is also used to keep the slurry level consistent, ensuring the stability of the mud wall. -
Materials Used
Guide walls are constructed using either cast-in-place reinforced concrete or prefabricated steel structures. -
Construction Methods
Guide walls are constructed in stages: site leveling, layout marking, trenching, reinforcing, formwork setup, pouring concrete, and curing.
Mud Wall Protection:
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Mud Composition and Function
Bentonite slurry is typically used for its ability to support the walls and carry sand and soil particles. The slurry helps to cool the drilling equipment and reduce wear. -
Slurry Preparation
Slurry is mixed using high-speed machines, and its properties are carefully controlled to maintain the right density and viscosity. The slurry should be replaced or treated regularly to ensure consistent performance.
Excavation and Slotting:
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Key Considerations
The accuracy of excavation is crucial, particularly for maintaining vertical alignment. The depth and precision of the excavation should meet the required specifications to avoid wall instability. -
Slot Length Determination
Factors such as soil conditions, machinery capacity, and time constraints impact the length of each excavation segment, typically ranging from 3 to 8 meters. -
Slurry Wall Stability
Maintaining proper slurry density is vital to prevent the walls from collapsing during excavation. Regular checks ensure the slurry’s consistency.
Reinforcement Installation:
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Reinforcement Cage Construction
The steel reinforcement cage is assembled and placed into the excavation slot. This cage must be precisely aligned and securely placed to ensure the strength of the final wall. -
Concrete Pouring Process
Concrete is poured into the reinforced slot using a concrete pipe system. The pour must be continuous and evenly distributed to avoid air pockets and ensure a solid, uniform structure.
Conclusion
Diaphragm wall construction plays a vital role in providing support for deep excavations and large underground structures. Despite the challenges, including the high cost of temporary walls and the management of slurry waste, the advantages of using diaphragm walls, such as increased structural integrity, adaptability to various geological conditions, and faster construction times, make them an invaluable solution in modern construction projects.
Proper planning, execution, and attention to detail during each phase of construction ensure that diaphragm walls are both cost-effective and reliable, contributing significantly to the overall success of the project.
