When constructing bridges and other structures in deep water, safety, ease of foundation work, minimizing environmental impact, and construction costs are paramount. One of the most effective solutions for achieving these objectives is the use of a steel pipe pile underwater platform system for drilling piles in submerged areas. This method ensures ease of construction and reliability while reducing disruption and costs.
Key Features of the Construction Method
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Efficient Land-Water Connectivity: The method ensures seamless connection between land and water, effectively solving transportation issues in underwater environments, with a focus on safety and reliability.
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Simple Platform Construction: The construction process involves building simple platforms that are easy to set up. Even workers without prior experience in aquatic environments can successfully operate on these platforms without issues such as seasickness.
Applicable Scenarios
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Deep Water Foundation Construction: This method is ideal for foundations in waters up to 30 meters deep.
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Bridge Foundations in Reservoirs, Rivers, or Bays: It is well-suited for deep water foundations of rail and highway bridges crossing bodies of water like reservoirs, rivers, or bays.
Construction Process
Process Principle
The construction process involves assembling floating cranes using floating boxes, I-beams, trusses, winches, and rotary bases. The floating crane is used to position the guide ship made of floating boxes and I-beams. This guide ship acts as a frame for steel pipe pile installation. The construction process is carried out in stages, starting from pile installation, platform construction, drilling, and then moving on to reinforcement cage installation and concrete pouring.
Process Flow
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Production of Steel Pipe Piles and Steel Casing: Steel pipes and steel casings are fabricated on-site. Typically, 10–14 mm-thick steel plates are rolled into smaller sections, which are then welded together to form larger sections. The steel pipes are welded with an internal and external circumferential weld with a minimum width of 2 cm.
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Assembly of Floating Boxes: Floating boxes, composed of several smaller steel boxes, form the base for the floating crane. Each box is rectangular with rounded corners on the bottom. The steel plates used for the boxes are 3mm thick, and internal steel partitions are included. The boxes are bolted and pinned together, and anchor bolt holes are left for future equipment connections.
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Assembly of Floating Crane: The floating crane is made up of floating boxes and a CWQ20-type dismountable mast crane. The crane consists of arms, vertical columns, bracings, a turntable base, and a driver’s cabin. The crane has a maximum lift capacity of 20 tons, with a lift range of 4.54 to 20.67 meters.
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Platform Construction in Water:
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Anchoring the Floating Crane: The crane is used to anchor a concrete block (weighing around 10 tons) at a distance of 60–100 meters from the designated pile location. A float tube marks the location.
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Positioning the Guide Ship: The guide ship is anchored at the designated pile position. The crane is used to position the ship and install the steel pipe piles using a winch system.
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Installation of Steel Pipe Piles: Once the guide ship is positioned, steel pipe piles are transported by a tugboat and lifted into position using the floating crane. The piles are gradually lowered into the riverbed, with adjustments made to ensure vertical alignment.
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Installation of Steel Casing: After positioning the piles, the next step involves installing a steel casing at the pile location. The casing is carefully lowered into place using the crane and vibratory hammer until it reaches the required depth.
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Drilling and Pile Foundation Construction: Once the casing is installed, a drilling machine is positioned to start drilling the pile foundation. This is followed by slurry removal using a reverse circulation method, ensuring that the hole is cleaned and ready for concrete pouring.
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Concrete Pouring: Concrete is mixed on-site and delivered to the project area via a temporary dock. A conveyor system is used to transport the concrete to the barges, where the floating crane is used to pour it into the drilled pile hole.
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Platform Demolition: After the pile foundation is completed, the construction platform is dismantled in stages, starting from the top and working down to the base.
Case Study: Construction of the Youxi Interchange Bridge
The Youxi Interchange Bridge spans the Youxi Reservoir and is a key infrastructure project with 6 underwater foundation piers. The foundation piles are 2.2 meters in diameter and up to 49 meters long. The water depth at the construction site is up to 18 meters, and the reservoir’s water level can fluctuate by up to 3 meters during heavy rains. The project used the steel pipe pile underwater platform method to efficiently construct the piles in the challenging deep-water environment.
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Overall Approach: The bridge’s small span and scattered piers made the steel pipe pile underwater platform method the most efficient and cost-effective solution.
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Construction Platform: The platform for the bridge’s piers was constructed based on the steel pipe pile layout, with adjustments made to accommodate varying pile distances. Each underwater pier required a 15×8-meter work platform.
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Floating Crane Specifications: The project utilized a CWQ20-type crane with a lifting capacity of 20 tons and a lifting range of up to 20 meters.
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Production of Steel Pipe Piles and Casing: Each steel pipe pile was fabricated on-site, with lengths ranging from 16 to 23 meters. The casing was fabricated to the required lengths and welded together before installation.
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Pile Installation Process: Steel pipe piles were carefully lowered into the riverbed, with monitoring equipment ensuring that they reached the required depth and remained vertical during installation.
Conclusion
The use of steel pipe piles and floating platforms for underwater pile foundation construction provides an efficient, safe, and cost-effective solution for bridge and other infrastructure projects in deep water. This method offers several advantages, including reduced construction time, lower environmental impact, and greater ease of use for workers with minimal water-based experience. Through careful planning, proper equipment, and innovative techniques, this approach ensures the successful completion of complex underwater foundation projects.
