I. Project Overview and Construction Objectives
Dock ramp slide tracks (commonly used in ship launching or docking slopes) are prone to corrosion from seawater, mechanical wear, and biological fouling when submerged for extended periods, leading to reduced surface flatness and weakened structural integrity. Underwater maintenance objectives include:
Repair surface damage to the slide track (cracks, dents, corrosion pits).
2. Restore the track flatness and friction coefficient to ensure safe passage for vessels.
Enhanced track durability, extending service life.
II. Construction Preparation and Conditions Confirmation
1. Technical Preparedness
Verify design drawings: Confirm slide material (steel/concrete), structural type, and damaged areas.
○ On-site Inspection: Conduct detailed checks on the slide surface, welds, and junctions using divers or ROVs (underwater robots), recording the type and extent of damage.
Develop a specialized construction plan: Specify repair methods, materials, equipment, and safety measures.
2. Materials and Equipment
○ Repair Materials: Non-dispersive concrete underwater, epoxy mortar, anti-corrosion coatings (such as epoxy glass flake), stainless steel repair plates, etc.
○ Construction Equipment: Diving Equipment (including ROVs), underwater cutting tools (plasma cutters), welding equipment (wet welding or localized dry chamber), high-pressure washers, grouting equipment, etc.
○ Auxiliary Tools: Total Station (Positioning), Sonar (Water Depth Detection), Underwater Grinding Machines, etc.
3. Operating Conditions
Temporarily close off the operational water area and set up warning signs.
Choose to conduct construction during low tide or when currents are calm. Drainage or pressure reduction may be necessary.
Divers must complete decompression sickness prevention training and equipment safety checks prior to operation.
Section 3: Maintenance and Construction Process
Area with damage cleaned
Remove marine organisms, rust layers, and loose concrete from the surface, then wash with high-pressure water jets to expose a solid base.
○ For steel structural tracks, use sandblasting to achieve Sa2.5 rust removal, and clean the oil污 around the weld seams.
2. Local Repairs and Reinforcements
Concrete滑道修复：
Crack Treatment: Infiltrated with underwater epoxy grout to seal the cracks.
凹坑修复: Pour underwater non-segregating concrete, control the pouring area with molds, and compactly vibrate.
■ Large-scale Repair: Remove damaged areas, re-pour high-strength concrete, curing period of not less than 7 days.
Structural Steel Sliding Track Repair
Weld Seam Repair: Wet welding or local dry tank welding, non-destructive testing (MT/UT) to confirm weld quality.
Corrosion pit repair: Cut away the corroded area, weld in stainless steel patch plate, and grind the surface smooth.
3. Surface Treatment and Protection
The overall slide track is coated with anti-corrosion coating (such as thick film epoxy coating + polyurea topcoat), enhancing resistance to seawater corrosion.
For high-wear areas, embed wear-resistant ceramic particles or apply a stainless steel wear-resistant coating.
4. Functional Verification
Flatness Measurement: Utilizing a laser scanner to measure the track surface flatness, error is controlled within ±3mm.
Friction Coefficient Test: Meets ship passage safety standards (typically ≥0.35).
Underwater Camera Inspection: Verify no leaks or cracks in the repaired area.
4. Key Technical Points
Submerged Concrete Casting Technology
Select concrete with high anti-dispersion properties to prevent cement loss.
Cast using the pipe method, controlling the pouring speed to prevent bubble entrapment.
Avoid water flow erosion during maintenance; cover with a protective net if necessary.
Welding Quality Control
○ Wet welding requires special welding rods (such as AWS D3.6M) and controlled current to prevent brittleness.
Seal the welding area for dry hold welding, then vacuum and weld to ensure weld quality.
3. Corrosion-proof coating application
Coating thickness as per design specifications (typically ≥300μm), layered application to prevent wrinkling.
Avoid mechanical damage during curing of the coating; no entry allowed.
V. Safety and Quality Control
Safety Measures
Divers operate in strict compliance with the "Safety Regulations for Diving Operations Underwater" (GB/T 26123) and are equipped with emergency oxygen supplies.
The construction area is equipped with dual protection (warning buoys + fences) to prevent unauthorized vessels from entering.
High-pressure and welding equipment are operated by trained personnel to prevent electric shock or fire.
Quality Control
Material Incoming Inspection: Verify the qualification certificate and take samples for mechanical property testing.
On-site supervision during construction, 100% acceptance for critical processes (such as welding, pouring).
After repair, conduct functional testing in accordance with the "Port Civil Engineering Construction Code" (JTS 215).
6. Common Questions & Solutions
Low underwater visibility: Use ROV for auxiliary positioning; divers equipped with lighting equipment.
2. Stream Impact on Construction: Install temporary diversion plates or use air bags to seal upstream to reduce water flow.
3. Insufficient coating adhesion: Resurface and achieve the required roughness if the preliminary treatment is inadequate.
Section 7: Summary
Dock apron slide track underwater maintenance requires precise detection, efficient repair, and long-lasting protection. Ensuring the track's functionality is restored and durability enhanced, strict quality control and safety measures are employed. It is recommended to be carried out by a professional team with port engineering qualifications and regular maintenance inspections should be conducted.
