6.11 Application of corrosion protection

6.11.1 General

The principles of protection are the same for all parts of the anchor but different detailed treatments are necessary for the tendon bond length, the tendon free length and the anchor head.

The protective system shall not restrict any stressing or destressing operation nor be damaged by it. A lubricant or bond free contact shall be present within either the individual sheaths or the common sheath to ensure free movement of the tendon(s) during stressing.

Particular care shall be taken to seal transition points from one protection component to another and at end points.

The ground anchor or any part of it shall be handled in such a way that the corrosion protection system is not damaged.

6.11.2 Tendon free and bond lengths

Tendons shall be free of corrosion, in particular pitting corrosion, when they are encapsulated by a corrosion protection system. Slight surface rust is permissible, providing it can be wiped off, and the surface is subsequently covered by cement grout.

Tendon protection to the free length of a temporary anchor may be applied in situ, on site, or prior to delivery. Tendon protection to the bond length of a temporary anchor is generally applied in situ.

Where corrosion protection of permanent anchors is applied by means of plastic sheaths and ducts, permanent tendon sheaths, resin or cement grouts and corrosion preventive compounds prior to the installation of the tendon in the borehole, this should be done either under factory conditions or on site within specially constructed work areas where dry air and clean conditions can be assured. The environmental conditions shall be such that the application of corrosion protection may be undertaken in accordance with this standard.

Where corrosion protection of permanent anchors is applied in situ by means of plastic sheaths and ducts, permanent tendon sheaths, metal ducts, resin or cement grouts and corrosion preventive compounds, care should be taken to ensure that the tendon and metal duct are kept clean and free of corrosive materials during this operation.

Grouting of the encapsulation of permanent anchors shall be undertaken from the lower end of the sheath and shall be continuous until completed.

The tendon shall not be exposed to deleterious stray currents.

6.11.3 Anchor head

Where the environment is aggressive, early protection of the anchor head shall be applied to both temporary and permanent anchors.

The purpose of the inner head protection is to provide an effective overlap with the free length protection, to protect the short exposed length of tendon below and passing through the bearing plate.

Where injection techniques are employed, a lower injection pipe and upper vent pipe should be used to ensure complete filling of the void. Where no access for injection of the inner head is provided, a prepacked corrosion protection compound may be used.

Where restressability or load checking is not required, resins, grouts and other setting sealants may be used within the anchor cap. Where restressability or load checking is required the outer head protection including the anchor head cap and its contents shall be removable. It shall be possible to refill the cap with corrosion protection compound.

A suitable seal and mechanical coupling shall be provided between the cap and the bearing plate.

Where applied to permanent anchors the bearing plate and the other exposed steel components at the anchor head shall be protected in accordance with the relevant EN for the coating of steel structures prior to being brought onto site.

Steel caps for permanent anchors shall have a minimum wall thickness of 3 mm.

Reinforced plastic caps having a minimum wall thickness of 5 mm may be used, where approved by the Client's Technical Representative.

The protection system applied to the inner and outer anchor head shall be subjected to a system test (see 6.12).

EN 1537:1999 Execution of special geotechnical works – Ground anchors