I. Project Overview and Construction GoalsDuring the process of sealing the well bottom, the steel cage may require underwater cutting due to design changes, construction errors, or cleaning requirements. The cutting target is:
Precisely cut the specified section of the reinforcing cage to ensure smooth subsequent construction of the sinking well.
2. Maintain precise cutting to prevent damage to the well casing structure or adjacent steel bars.
Ensure safety during cutting operations, prevent risks such as collapses and electric shocks.
II. Construction Preparation and Conditions Confirmation
1. Technical Preparation
Verify the cofferdam design drawings, confirming the diameter and specifications (model, spacing) of the reinforcing cage, as well as the concrete strength grade.
Diver or ROV underwater inspection: Record the position, misalignment, and distribution of underwater obstructions.
Develop a specialized cutting plan, specifying the cutting sequence, equipment selection, and emergency response measures.
2. Equipment and Materials
○ Cutting EquipmentUnderwater plasma cutting machines, underwater grinding machines, conical iron abrasive grinding wheel drills (mechanical cutting), high-pressure water jet equipment (optional).
○ Auxiliary ToolsDiving equipment (including ROVs), underwater welding equipment (spare), tension force measurement devices.
○ MaterialsRapid-setting cement (temporary sealing), sacrificial anode (corrosion prevention and backup).
3. Job Conditions
The working area is temporarily closed, and warning signs are set up to prevent vessel interference.
Construction during low water levels or slow flow periods; diversion and pressure reduction as necessary.
Divers have completed decompression sickness prevention training and equipment safety inspections.
Section 3: Cutting Construction Process Rebar cage positioning and cutting point marking
Divers or ROVs should precisely locate the cutting point (preferably near the concrete surface).
● Mark cutting lines using underwater marking pens or laser locators to ensure precision.
2. Cutting Method Selection (Based on Rebar Diameter and On-site Conditions)
● Mechanical Cutting (Recommended)：
Use conical iron sandwheel drill bits or hole-bottom enlargement drill bits to gradually grind the rebar.
○ Key Operations:
The drilling machine centers the drill bit and gently lowers it to the cutting area.
Move the drill machine forward, backward, left, and right to ensure full circumferential cutting of the rebar (multiple cycles required).
After grinding, tensile force test is conducted: If there is no elongation at 18t tensile force, the steel bar has not been cut, and further grinding is required.
● High-pressure water jet cuttingSuitable for small to medium diameter rebars, with no thermal effects, but requires high-pressure equipment support.
● Underwater Plasma CuttingHighly efficient with smooth cuts, but significantly affected by water flow; requires professional operation.
3. Cutting Implementation and Inspection
● Cut in segments according to the predetermined sequence to prevent the overall structure from becoming unstable.
After each cut, use a tensile force device to check if the steel bar is completely severed.
If the tensile force is low and the elongation is significant, the steel bar has been cut.
If the tensile force is high with no elongation, continue to grind until it is cut through.
After cutting, divers clean up the debris to ensure no remnants affect subsequent construction.
4. Temporary Sealing and Reinforcement (Optional)
If local concrete is exposed due to cutting, quick-setting cement can be used for temporary sealing to prevent leakage or collapse.
● Sacrificial anodes can be added to critical areas to enhance the structural anti-corrosion capability.
4. Key Technical Points
1. Cutting Precision Control
Prefer cutting close to the concrete surface to minimize slippage or drill jamming caused by steel reinforcement deflection.
Utilize a positioning ruler or ROV for real-time monitoring of cutting depth.
2. Equipment Operation Guidelines
○ Submerged grinding wheel machines must be equipped with a protective shield to prevent debris from flying and causing injury.
Pay attention to current control in plasma cutting to avoid arc ignition of surrounding combustible materials.
3. Steel Reinforcement Cage Stability Monitoring
During cutting, assign a dedicated person to monitor the settlement well structure for deformation, and immediately halt operations upon detecting any anomalies.
In case of necessity, temporarily reinforce uncut steel bars to prevent overall toppling.
V. Safety & Quality Control
1. Safety Measures
Divers strictly adhere to the "Safety Regulations for Underwater Operations of Divers" (GB/T 26123) and are equipped with emergency oxygen supply systems.
Construction areas are equipped with double-layer protection (warning buoys + fences), and high-voltage equipment is operated by designated personnel only.
○ Equipped with backup cutting equipment and rapid water-stop materials to handle unexpected leaks.
2. Quality Control
After cutting, the flatness of the cut and the steel cutting effect are confirmed through underwater camera inspection or non-destructive testing (ultrasonic).
Before the concrete pouring for the well-casing, verify that the reinforcement cage cutting position meets the design requirements.
6. Common Questions & Solutions
1. Card drillReduce initial cutting speed to prevent the drill bit from being caught by rebar; if the drill bit is caught, use reverse rotation or a jack to assist in releasing it.
2. Low cutting efficiencySelect drill bits with appropriate diameters (e.g., a conical iron sand wheel with a diameter of 0.9m is suitable for a 1.3m steel cage), and allocate the grinding paths reasonably.
3. Water Flow InterferenceTemporarily redirect flow or add weight blocks to stabilize the drilling rig, and use ROV for auxiliary positioning if necessary.
Section 7: SummaryCaisson underwater bottom steel cage cutting requires precise positioning, efficient equipment, and strict safety measures. Ensure construction safety and quality through step-by-step cutting and real-time monitoring. It is recommended to be carried out by a professional underwater construction team and refer to the "Underwater Welding Code" (AWS D3.6M) and "Port Hydrological Structure Construction Code" (JTS 215).
