Planning and Estimating Data for Steel Pile Maintenance Using Cathodic Protection
Description of Task: Install a sacrificial anode on a steel pile below low waterline. A 40-pound anode is attached to the pile with a welded connection.
Size of Crew: Dive station, one laborer.
Special Training Requirements: Familiarity with removal of marine growth, underwater lifting procedures, and underwater welding.
Equipment Requirements: High-pressure waterblaster, hydraulic grinder with Barnacle Buster attachment, high-pressure pump for wateiblaster, hydraulic power unit, welding machine with leads, welding torch, lift bags/rigging gear, float stage or work platform.
Procedure: The location and attachment method will vary depending on the specific application site. The system should be designed by an experienced corrosion engineer. Attachment methods may include bolting, welding, or explosively-actuated fasteners.
Productivity of Crew: 1-1/2 hour per anode. Materials:
Anodes - A sacrificial anode should be placed on each pile to be protected for maTimnm protection. Wire leads can be run to diagonal or horizontal bracing members between piles and bonded in place for further protection.
Small holes in steel sheet pile structures, 1/2 inch to 1 inch, can be covered with epoxy patches as described in Table 5-13 with planning and estimating guides in Table 5-14. Manufacturers of underwater curing epoxies are listed in Appendix A.
A successful bond between the epoxy and steel surface requires thorough cleaning of the sheet pile surface. All marine growth and loose rust must be removed and the surface cleaned to bare metal. A rough surface provides better gripping power for the epoxy patch. Mechanical cleaning tools and a high-pressure waterblaster can be used for cleaning below the waterline. The epoxy material must be applied within 72 hours (less for warm waters) following cleaning before new growth has a chance to form. Epoxies will not stick to wet surfaces. Therefore, the technique used is to smear the epoxy (kneaded and pressed) over the surface to drive off the water and produce an intimate contact between the epoxy and sheet pile surface.
Each manufacturer has a specific set of instructions which will include application methods, hazard warnings, pot life after mixing, and minimum cine temperatures.
Most underwater epoxies will not cure below 50 °F. However some manufacturers have special formulations of resins to cure at temperatures down to 40 °F. The cure time increases as temperature drops: a low temperature epoxy might take 24 hours to achieve an initial cure and up to 14 days to achieve maximum strength. It is also noted that the maximum strength of epoxy cured at 40°F will be significandy less than the same epoxy cured at 60 °F.
Underwater epoxies are hazardous materials and require appropriate shipping and handling procedures. Wear protective gloves during mixing and applying.
Epoxies can be used as gasket material in conjunction with steel, wood, or plastic sheet patches. Various mechanical fasteners are used to join the patches to the sheet pile (toggle bolts, stud gun, etc.). Care must be taken to ensure that the patch and fastener material does not create accelerated corrosion problems. The use of nonmetal-lic patch and fastener materials is preferred.
Where there are too many holes to cover practically with small patches, a technique that may be used is to cover the large holes with patches and use pressure grouting techniques to fill voids behind the wall as illustrated in Figure 5-19. Pressure grouting requires specialized equipment which may not be readily available for UCT operations.
A number of techniques can be used to repair a deteriorated sheet pile wall. Before proceeding with the repair, it is important that a structural analysis be made to validate the soundness of the existing sheet pile to carry additional load from a new cap or concrete face and determine the need for additional tiebacks.
Replacement of die deteriorated top of the steel sheet pile retaining wall structure may be accomplished by installing a cast-in-place concrete cap on the wall as described in Table 5-15. The repair may also require partially coating the front and back surfaces with concrete.
As in the case of partial concrete encasement of pipe and H-piling, accelerated corrosion can occur at the bottom of a partial concrete encasement of sheet steel piling. Ideally, the encasement should be terminated above MHW and continued to below the mudline. Alternatively, cathodic protection should be installed to control the accelerated corrosion attack.
Patching Small to Medium Holes in Steel Sheet Pile
Problem: Small to medium holes exist in sheet pile wall, condition of sheet piling is sound with minor corrosion (Figure 1).
Description of Repairs: Thoroughly clean area to be repaired removing all marine growth, rust scales, loose materials and debris.
Epoxy Patch: Use only for minor repair of small holes/pits. Follow manufacturer's directions. Use protective rubber gloves while mixing materials. A rough irregular surface will provide a better bond. Technique generally not effective below 55°F water temperatures.
Smear mixed epoxy material over area to achieve uniform coverage. The smearing action displaces water at the surface providing necessary contact between epoxy and surface. Fiberglass cloth may be used for reinforcement
Steel Plate Patch: Determine size of patch and prepare patch to fit needed contour. Select method of attachment. Fabricate gasket and install patch.
• Alternative Patch Materials:
- Cut and bent steel plate is fitted over damaged sheet pile
- Locate a section of steel or plastic sheet pile with the same contour as the seawall.
• Methods of attaching patch to sheet pile wall include:
- Drive studs with stud gun and bolt patch in place
- Use a Tucker Patch technique on larger holes
- Weld patch in place if experienced underwater welder available (generally not recommended)
- Use toggle type bolts or bolts with L-shaped ends to catch pile wall
A gasket between patch and seawall can provide a seal to reduce surge or current-induced washout of back fill material. Gasket materials include:
• Fabricate a gasket from sheet rubber
• Apply wide grouting bead of flexible material to patch and allow to set before installing
• Apply underwater epoxy grouting material to seawall just prior to installing patch
Alternatively install patch without gasket and use pressure grout techniques either through die patch or from the surface to fill behind patch and seawall.
Application: This technique will not prevent further corrosion and its success is dependent on the soundness of the surrounding sheet pile. Continued deterioration particularly near wale and tieback rods could lead to seawall failure. Obtain engineering assistance for guidance.
Epoxy Patching of Steel Sheet Pile Wall
Was this article helpful?