Summary of Decades of Experience in Bridge Construction by a Senior Engineer

In this article, we present a comprehensive summary of decades of bridge construction experience by a chief engineer. The content is rich in practical insights and is a valuable resource for anyone in the construction field.

1. Site Preparation and Layout

No matter the size of the project, site leveling is essential. Upon entering the site, a thorough site preparation and layout should be carried out to ensure enough space for the main construction activities. In municipal engineering, where space is often limited, careful site layout is crucial. Once the site is leveled, it becomes conducive to machinery operations, maximizing the efficiency of machinery and reducing labor costs. In large-scale projects, building high-standard roads initially is an investment in long-term savings rather than waste.

2. Foundation Construction

Bridge foundations often use pile foundations, which can come in various forms. Large bridges typically employ bored piles and cast-in-place piles. Here, we will focus on bored piles and cast-in-place piles.

a) Bored Piles

Bored piles are commonly used in bridge construction, especially for underwater engineering. The construction process involves the following steps:

1. Process Flow:

   • Drilling and preparation

   • Reinforcement cage installation

   • Concrete pouring

2. Quality Control During Construction:

   • Ensuring proper hole alignment and depth.

   • Checking reinforcement cage fabrication and placement.

   • Preparing the drilling mud and performing secondary cleaning before pouring concrete.

   • Strictly inspect materials before use to ensure compliance with quality standards.

Quality control for pile foundations is essential and requires dedicated site management. The focus should be on prevention, with detailed attention to every phase of construction to ensure top-notch quality.

b) Rotary Drilled Piles

Rotary drilled piles, compared to bored piles, have distinct hole-forming techniques. This method is highly effective for environmental protection and is widely used in municipal projects.

1. Construction Requirements:

   • Pile verticality should be maintained with a deviation of no more than 0.5%.

   • Reinforcement cage fabrication tolerances should be within ±10mm for main bars and ±20mm for ties.

During the installation of rotary drilled piles, care must be taken to avoid deformation and misalignment of the reinforcement cage. Post-construction, a curing period of 24 hours is necessary before proceeding with adjacent piles.

c) Manual Excavated Piles

Manual excavation piles are widely used due to their large bearing capacity and relatively easy construction. These piles are particularly suitable for soil conditions with good compaction, where the pile length is approximately 10 meters. However, this method requires significant labor and poses risks, such as hole collapse during excavation.

3. Foundation Pit Excavation

Excavation of foundation pits must follow specific guidelines:

1. Precise Measurement:

   • Establish the center and control stakes based on construction drawings.

   • Use machinery and manual labor to carefully excavate the pit, avoiding damage to pile foundations.

   • After excavation, check and verify the pile positions and mark the required levels.

2. Soil Compaction:

   • Ensure that no soil is over-excavated. Excessively loose or unstable areas should be compacted to guarantee a stable foundation.

3. Pile Entry Preparation:

   • For piles embedded in bridge abutments, markings should be made on the pile top to ensure proper cutting to the required height.

4. Pile Foundation Testing

Testing of pile foundations ensures compliance with standards and verifies the integrity of the construction. This is a crucial step in maintaining quality assurance.

5. Bridge Substructure (Pier, Cap, and Beam) Construction

The substructure includes elements such as beams, caps, and piers. The construction process is similar across various components and involves reinforcement, formwork, and concrete pouring.

1. Reinforcement Placement:

   • Clean the base layer and mark the reinforcement layout according to construction drawings.

   • Use appropriate supports to prevent sagging of surface reinforcements.

2. Formwork:

   • Typically made from bamboo plywood or steel, formwork needs to be checked for stability and proper alignment. Ensure that the joints are sealed to prevent leakage during concrete pouring.

3. Concrete Pouring:

   • Use high-quality concrete, ensuring it is pumped and poured continuously to avoid seams and air pockets. Perform regular inspections to verify the mix quality and cure the concrete properly.

6. Foundation Hardening and Soil Treatment

For projects that require foundation stabilization, methods like compaction and reinforcement are utilized to ensure a solid base. Water drainage around the foundation is also essential to prevent water accumulation and soil erosion.

7. Support Systems

For bridge construction, adjustable scaffold systems like the cup-lock scaffolding system are commonly used. This system is versatile and can withstand varying loads depending on the design.

1. Load Calculations:

   • Ensure that the design of the scaffolding can handle the load of materials and workers. Each vertical support should be analyzed for capacity, with detailed calculations to prevent collapse.

2. Scaffolding Layout:

   • Proper spacing and secure connections must be ensured throughout the scaffold, with safety measures to protect workers during assembly and disassembly.

8. Pre-Loading Support Systems

Before heavy concrete work, the scaffolding system must be pre-loaded to simulate the stress conditions during the construction process. This helps test stability and ensures safety.

1. Pre-Load Testing:

   • Apply the designed loads incrementally to monitor the system’s response and adjust accordingly to prevent issues during the actual construction.

2. Monitoring and Observations:

   • Use high-precision tools to measure any deformation or movement in the scaffold system, ensuring that adjustments are made promptly.

9. Formwork Engineering

For large-scale concrete elements like box beams, formwork is usually made from high-quality materials such as bamboo, plywood, or steel.

1. Fabrication and Installation:

   • Pre-fabricate and install formwork as per the structural requirements of the project. Regular inspection ensures that the forms remain stable and precise during the pouring of concrete.

2. Formwork Removal:

   • Wait for the concrete to reach the necessary strength before removing the formwork. Follow the specific timing outlined in the construction plan to avoid damaging the structure.