Weathering of pyritic mudrocks results in the oxidation of sulfides and generation of sulfates in concentrations potentially hazardous to civil engineering works. Geochemical and petrographic analyses undertaken on samples from sites underlain by the Kimmeridge Clay Formation and Oxford Clay Formation proved three distinct zones: an upper sulfur-leached zone, an intermediate weathered zone with sulfate-rich horizons and a lower relatively unweathered zone of low-sulfate, high-sulfide material. It was found that water-soluble sulfate and total potential sulfate may vary by up to 1500 mg SO42− l−1 and 8% SO42− respectively, over a depth interval of only 0.2 m. A targeted sampling strategy and ground aggressivity assessment approach can be applied to these formations based upon the sulfur species zones identified.

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