The effects of steel corrosion on the interface shearing behaviour of chalk

The ALPACA axial pile load tests conducted at St Nicholas-at-Wade in Kent, UK, proved axial pile shaft ca-pacity gains over time, or ‘set-up’, that were most rapid and marked for oxidizable steel piles installed with their tip depths above the water table. Comparable stainless-steel piles showed far less set-up under the same conditions, and all types of piles showed less long-term set-up beneath the water table. This paper describes laboratory research that examined hypotheses regarding the role of corrosion linked set-up in chalks under a range of environmental conditions. A series of metallurgical mass loss and electrochemical experiments was designed to assess the corrosion potential of the different steels used at the ALPACA site, in combination with different chalk strata and pore water chemistries. These tests, performed in collaboration with Tata Steel (Swansea, UK), were accompanied by steel-chalk interface tests involving combinations of steel types, chalk pore water chemistry and interface roughness that assessed how corrosion affected interface shearing behav-iour. Corrosion reaction rates with time for various steels and environmental conditions are reported along with short- and long-term trends for steel-to-chalk interface friction angles.