Mudrocks as Soft Rocks: Properties and Characteristics

Abstract

Soft rocks comprise the geological materials with poor mechanical characteristics that span the range between soils and hard rocks. Mudrocks are part of the broader group of soft rocks which correspond to fine-grained, clay-rich detrital sedimentary rocks. As mudrocks constitute more than 60% of all sedimentary rocks and occur frequently in geological sequence, they are often encountered in construction sites either in their natural undisturbed state or as construction materials. Mudrocks can show a range of engineering behaviours as function of their composition and structural features; however, by reputation, they are regarded as poor engineering materials in construction displaying low strength and durability as well as susceptibility to volume changes. This chapter aims to provide a framework of the main geological and engineering geological aspects of mudrocks that control their engineering properties and behaviour. With this concern, the key controls on the formation of mudrocks, the terminology used to classify fine-grained sedimentary rocks and the main geological and geotechnical characteristics of mudrocks, including the relevant laboratory techniques are presented as well as the geological and engineering geological classifications of mudrocks are reviewed. Finally, a set of case studies of mudrocks encountered in commonly occurring civil engineering works are described.