Steel Piles

As described in Section 3.4, there are a number of different causes of deterioration of steel in the marine environment. There are also many methods for the repair and maintenance of steel piles. Selecting the method to be used depends on: (1) the extent of the damage, (2) economics of the repair, and (3) physical and environmental factors at the site.

The pile plays an important role in the integrity of the overall structure and deterioration can result in serious reduction of the capacity of the pier or structure. Therefore, it is important that an engineering structural analysis be conducted to verify that the repair method will provide the needed structural support for the intended application.

CAUTION Before beginning construction operations, block off construction area from all traffic. Notify port authority to secure marine traffic in the area and obtain clearances to proceed from appropriate local authority.

Repair and maintenance methods fall into five general categories:

• Concrete encasement

• Partial replacement

• Complete replacement

• Coatings/wrapping

• Cathodic protection

5.5.1 Concrete Encasement

An outline of the procedures for repairing steel piles using concrete encasement is provided in Table 5-7. Planning and estimating data are included in Table 5-8. Some general information is provided below. Refer to the figures in Table 5-7 for an outline of the procedure. The repair procedure involves:

• Cleaning the pile

• Installing steel reinforcing, spacers, and forms about the pile

• Pouring concrete to fill the space between the pile and the form

Nonmetallic spacers are used to: (1) maintain a uniform concrete thickness, and

(2) ensure a minimum (1-1/2 indies) distance between pile and reinforcing steel and reinforcing steel and form. Each form manufacturer provides detailed instructions relating to installing their specific designs.

Both flexible and rigid forms are available and manufacturers are listed in Appendix A. Forms may also be fabricated from materials on site. Selecting the form type will depend primarily on availability and choice of the designer or construction crew.

Flexible forms fabricated from a porous fabric are usually left in place. Both open and closed top models are available. Open top fabric forms are usually suspended from the piling or overhead structure. A method for suspending open top flexible forms from sheet H-piling is shown in Figure 2 of Table 5-7. Open top forms are filled to overflowing. The concrete grout fill is topped with an epoxy cap or nonshrinking grout at a 45-degree angle as shown in Figure 5-17.

Rigid forms are open top and bottom and are normally removed and reused after the concrete has completely cured. Rigid forms can be commercial or fabricated from material found at the construction site. Translucent form jackets are recommended, as they provide the ability to view the level of the concrete, and to make corrections if there are any discontinuities in the repair material. Rigid forms require a bottom seal and base plate to hold the form in place. A temporary friction clamp and base plate conforming to the pile contour can be fabricated and attached to the pile at the bottom of the repair area (Figure 3 of Table 57). The rigid form rests on the base plate to form the bottom seal which prevents leakage of the concrete.

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Table 5-7

Repairing Steel Pile with Concrete Encasement

Procedure

Problem: Slight to moderate deterioration (less than 35 percent) of the cross-sectional area has occurred; or protection against corrosion and abrasion is required.

Description of Repairs: Flexible or rigid forms together with reinforcing are used to provide a concrete encasement around damaged pile. Follow form-manufacturer's directions. Install casing extending from 1 foot above MWH to 1 foot below mudline.

• Clean the steel pile of marine growth and loose rust. Use high-pressure water blasting if necessary.

• Install steel reinforcing mesh around the pile, using spacers to provide minimum 2-inch clearance between the pile and reinforcing, and between form and reinforcing.

• Blocking between form and pile (Figure 1) may be needed to seal bottom of form and prevent concrete leakage during filling.

• Pump concrete using 15-psi minimum pressure through suitable pipes or hoses extending to lowest point. Keep discharge end submerged in concrete.

Flexible Form Closed Bag Type: Figure 1 - Wrap the form around the pile with blocking at bottom; close zipper; secure form to the pile at top and bottom with mechanical fasteners or banding. Insert fill tube to bottom of bag and fill to overflow with concrete.

Flexible Form Open Top Bag: Figure 2 - Suspend fabric form from structure or friction clamp as shown in detail using turnbuckles, or chains to steel hanger ring. Install blocking and secure form to pile at bottom using banding or clamps. Fill with concrete.

Rigid Form Open Top: Figure 3 - Fabricate and install base plate to seal bottom and hold form in place. Install bands every 12 inches; install pump band at lowest possible point. Fill form with concrete grout pumping through lower pump band. Vibrate form to ensure full concrete placement within form. Leave forms in place; remove bands only after concrete has set.

Backfill mudline. Cap open top forms with epoxy grout to provide a 45-degree cap.

Application: The method will not restore full bearing capacity lost due to deterioration. Partial restoration may be gained by bolting steel angles, channel or plate to the piles before the concrete encasement (Figure 4). Obtain engineering guidance for strengthening requirements.

Pile Cap Construction Underwater

Table 5-7 Figure 1. Flexible form closed bag.

H-pile

Angle iron brackets friction clamps

Hook bolts, turnbuckles, or suspension chains

Suspender ring with swedge connector

Zipper

H-pile

Angle iron brackets friction clamps

Hook bolts, turnbuckles, or suspension chains

Suspender ring with swedge connector

Zipper

Mortar fill pipe Standoff

4x6 blocking

Caulking Mudline may be

Clamp over fabric

4x6 blocking

Caulking Mudline may be

DETAIL te<*uircd

Suspension hook

H-pile

Fabric

Cutaway view

Mortar fill pipe Standoff

Cutaway view

Clamp over fabric

Pile Cap Arranment

Suspension hook

H-pile

Fabric

Blocking as required for pile contour (see detail)

Reinforcing steel as required Bend in all tie wires ottom standoff

Bend in reinforcement steel top and bottom

Blocking as required for pile contour (see detail)

Table 5-7

Figure 2. Open top form arrangement.

Existing Pile Cap

Wire mesh or steel reinforcing

Existing Pile Cap

Detail Wrapping Mesh Concrete Encasement

Friction clamp-assembly to hold base plate

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Responses

  • tesfay
    How to form a seal around concrete pile underwater?
    3 years ago
  • senait
    How to repair steel h piles underwater?
    2 years ago

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