Report No. : GEO Report No. 135

Report Title : Long-term Durability of Steel Soil Nails (2003), 65 p.

Author : Y.K. Shiu & W.M. Cheung

Abstract

Steel soil nails are used extensively for slope improvement works in Hong Kong. A study has been carried out to review the effectiveness and reliability of the current corrosion protection provisions with regard to the long-term durability of steel soil nails.

The study comprises a review of relevant literature on corrosion of steel in soils and technical guidance documents from France, the UK and the USA. Based on this review and a survey of properties which reflect the corrosion potential of soils, it is found that a significant portion of the local soils tested could have a relatively high corrosion potential. However, the data available are fairly limited and only provide a general indication of the potential corrosivity of the soils tested. The corrosivity of a site depends highly on the site-specific conditions. As part of the study, five different types of corrosion protection provisions used for steel soil nails (viz. cement grout, sacrificial steel, sacrificial metallic coating, non-metallic coating and corrugated plastic sheath) have been examined. Two case studies on corrosion of steel soil nails (one in Japan and the other in Hong Kong) have also been reviewed.

It is concluded that at present there is not enough information to determine accurately the corrosion rates of steel and zinc coating in soils of different aggressivities.

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