The relevance of lithostratigraphy in the assessment and investigation of engineering ground conditions in UK mudstones = la pertinence du lithostratigraphy dans l'evaluation et la recherche sur les conditions au sol de technologie en argilite UK

Stratigraphy is the study of layered rock sequences, particularly in terms of their age and correlation with equivalent rocks elsewhere. It has many different branches of which some of the most fundamental are lithostratigraphy, concerning the subdivision of rock succession into units on the basis of their lithology and physical characteristics; biostratigraphy, involving the subdivision and correlation of the rock succession based on its contained fossils; and chronostratigraphy concerned with the subdivision and classification of rock successions according to their age. Lithostratigraphic subdivisions are those normally depicted on geological maps and sections and most commonly encountered in the ground engineering industry. However, because of local (site scale) lithological and property variations it is arguable that lithostratigraphic classifications are of only limited use for site-specific engineering, given that subdivisions are based on generally broad physical characteristics aimed at wider regional correlations. Practical use of stratigraphic subdivisions in ground engineering is further hindered by periodic changes to their nomenclature that has caused confusion to non-specialist users not fully aware of the reasons for making such changes. Despite these apparent limitations, recent research into the geotechnical characteristics of the Lias Group and Lambeth Group deposits in the UK has shown how lithostratigraphy can aid in anticipating regional trends in their characterisitics, properties and behaviour. The studies have also demonstrated how understanding regional geological controls can enhance site specific knowledge, leading to more focussed and cost effective ground investigation planning.