Implications for ground engineering through deterioration of landforms and geological materials caused by atmospheric reactions involving sulfide and sulfate minerals

The implications of sulfide and sulfate minerals on landforms and foundations vary significantly between temperate, arid and equatorial zones. Sulfur minerals, especially pyrite and gypsum, underlie significant engineering problems due to volumetric and mineralogical changes that occur following exposure to surface weathering environments. Whilst pyrite is stable under the anoxic reducing conditions in which it forms, exposure to oxygenated, damp environmental conditions result in rapid oxidation that produces chemically aggressive acidic, sulfate-rich solutions. If carbonates or cementitious material are present, potentially expansive selenite–gypsum is likely to be formed. In dry arid environments, these processes will occur more slowly, but their effects are often observed as dramatic slope failures. Dry environments are also conducive to the preservation of sulfate minerals such as gypsum and anhydrite in the ground. However, these minerals are liable to undergo dissolution and volume changes when disturbed by construction that may also create conditions that are chemically aggressive for concrete and other materials. The possibility of long-term impacts of weathering and changes brought about by the engineering works must be considered in ground investigation and geomaterials assessments, accounted for in the ground model, and addressed in the proposed design and method of construction. The intention of this paper is to outline some of the implications of sulfur minerals in geomaterials, provide guidance on the identification of potential problems in construction and landform evaluations, and suggest ways of avoiding difficulties.