Assessment of pyritic Lower Lias mudrocks for earthworks

Abstract

The weathering of pyritic mudrocks can have serious consequences for construction, and in particular for earthworks. Prediction of the likely behaviour of pyritic mudrocks involved in earthworks tends to be overlooked, with only the determination of aggressivity to steel and cementitious materials carried out. British Jurassic mudrocks tend to be soil-like overconsolidated deposits, typically with significant calcite and pyrite content. They may have appropriate engineering properties for earthworks under certain conditions, but they are susceptible to rapid atmospheric deterioration in the presence of both oxygen and water. The rate and products of pyrite oxidisation are dependent upon the mineralogy and fabric of the host material, its hydrological setting, and its immediate environment following exposure. This ultimately controls the rate and impact on construction. This paper outlines the construction through an area of Lower Lias mudrocks of Jurassic age for the A46 Newark to Widmerpool Improvement Scheme. The approach adopted allowed an understanding of the likely reactions and implications for construction at a site-specific level. This provided confidence for the client, designer and contractor that the adopted methodology was appropriate for long-term performance.