Diving Inspection Methods. During the inspection, divers descend with underwater cameras equipped with lighting, carrying small magnets, shovels, steel rulers, lead fishing sinkers with a line, and spotlights. They utilize real-time video monitoring systems to capture images of underwater structures. Divers communicate with surface monitors in real-time to ensure the quality of the recorded images and the detailed identification of structural defects, as well as to respond promptly to any emergencies.
Underwater inspection methods can be selected based on the actual workload and the specific inspection locations on-site. Inspectors may opt for the combined underwater camera inspection method, diving inspection method, or underwater robot inspection method to examine the submerged portion of the pier foundation. Combined underwater camera inspection method. The combined underwater camera inspection equipment is composed of an underwater camera, underwater illuminator, transmission cable, monitor, voice-over system, hoisting equipment (used for the up and down movement of the camera lens), and a barge (used as the work platform). During the inspection, the workboat is secured to the pier being inspected with ropes, and marking points for each shot are made on the water surface below the foundation.
To ensure the stability of the bridge structure after demolition, the method employed is the simultaneous cutting of the three-span suspended beams of the entire bridge. During the removal of the first and second spans (with the main beam being the span and the second span including the suspended beam being the main beam), the main beam including the suspended beam of the second span is first removed. Before the removal, the front support point is placed on the 1# pier's Bailey frame, and the rear support point is placed on the corresponding Bailey frame of the 2# pier. The other two suspended beams are pre-hung using a 300T crawler crane on the temporary bridge to achieve the stability of the other bridge sections after removal.
Attach the camera to the starting point of the desired inspection area using a hoisting device, and capture vertically. Maintain a distance of approximately 20-30cm (as clear visibility of the target is ensured) between the camera lens and the surface of the target object during shooting, and aim for smooth and uniform movement. After completing a vertical capture, slide or circle at the specified intervals along the base surface and continue shooting in the opposite direction. During the shooting process, ensure accurate recording and description. The advantages of the modular underwater camera inspection method are its fast inspection speed, low cost, and relatively safe operation for the inspectors. The drawback is that it requires a specific environment for effective inspection, i.e., clean water quality, no aquatic vegetation or microorganisms on the base surface, and the base submerged depth not exceeding 5m. Therefore, it is more suitable for inspecting the foundations of mountainous bridges and medium to small span bridges in plain areas, rather than large span bridges in plain areas or bridge foundations over seas.
Inspection and reinforcement of underwater structures require the use of underwater equipment or temporary sheet pile cofferdams, which are both costly and time-consuming. Japan's Goyou Construction Company has developed the Neo-Dry Repair Method (NDR technique) for reinforcing bridge piers by using a sinking steel box method to address the challenge of reinforcing underwater structures. This technique is a construction method designed to reinforce the underwater sections of piers by creating a dry working environment. It involves assembling a steel sinker box that is sunk around the pier, with reactive supports placed between the sinker box and the pier to counteract deep water pressure. A waterstop device is set at the bottom of the sinker box to form a watertight space, creating a dry working environment for reinforcement projects, suitable for underwater structure inspection, repair, and reinforcement in rivers and ports. The sinker box is composed of double-steel plate units that can be adjusted using buoyancy and assembled into a flat annular box around a specially reinforced structure, placed on the outside of the reinforcement. Waterstop structures are provided for waterproofing, with internal drainage ensuring a dry working space. Internal support segments are arranged between the sinker box and the specially reinforced structure, providing lateral water pressure balance for the sinker box after water removal. As the supports on both sides balance each other out, the entire temporary facility is a self-balancing system. The new sinking box dry work method completes reinforcement through limited underwater operations with the steel sinker box temporarily placed outside the pier, isolating the surrounding water, creating a dry working space inside the sinker box. This ensures the workability and safety of the reinforcement work. Since the sinker box can be reused, it offers good economic performance.
Underwater Bridge Demolition Safety Measures
1. Conduct thorough briefings for all workers, ensure they are certified before starting work, and strictly follow procedures and plans during construction. Implement the responsibility system for crane operators, require certification, and assign specific cranes and operators. Non-crew members are strictly prohibited from operating without authorization. Crane operators must concentrate and follow instructions during operations. Adhere strictly to the "Ten Do Not Hoist" and "Ten Do Not Allow" regulations during lifting.
2. Prior to hoisting, develop a reasonable and safe hoisting plan. Verify the crane's lifting capacity and swing radius, review the lifting points of the components, conduct a trial operation of the crane, inspect the lifting cables, clamps, and other equipment to ensure they are in good condition and have spare parts available.
Before lifting, perform a trial lift check. When the component is raised 20-30cm, inspect if the crane is stable and the wire rope and clamps are secure. Only proceed with the formal lifting operation upon confirmation of good condition.
4. During hoisting, avoid prolonged suspension or stopping; securely pull the wind-rope when lifting. Do not loosen the rope or disconnect the hook before the beam is properly aligned and corrected.
5. Operators should immediately stop the machinery and investigate any malfunctions or abnormal conditions with the assistance of others, rectify the issues, and then resume work.
6. Pay attention to weather conditions; in case of strong winds or heavy rain of level 5 or above, halt hoisting operations.
