The influence of diagenetic and mineralogical factors on the breakdown and geotechnical properties of mudrocks
John C. Cripps, Mourice A. Czerewko, 2017. "The influence of diagenetic and mineralogical factors on the breakdown and geotechnical properties of mudrocks", Geomechanical and Petrophysical Properties of Mudrocks, E. H. Rutter, J. Mecklenburgh, K. Taylor
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Mudrocks comprise fine-grained, sediments, in which the modal grain size is <0.063 mm and clay minerals are often major constituents. In geotechnics the term defines a generic group of argillaceous lithologies ranging from stiff clay-soils to strong, partly metamorphosed rocks. In the UK outcrops occur extensively and they also lie concealed beneath later deposits. In engineering applications mudrocks can present challenging forms of behaviour, including rapid deterioration and structural breakdown during sampling and preparation for tests. Attempts to measure their geotechnical properties are often frustrated and misleading results appear in the literature. A review of the engineering properties of UK mudrocks and studies involving mudrocks of varying induration demonstrates the importance of composition and genesis in controlling physical behaviour and provides a framework for understanding variation in mudrocks. Various index tests have been appraised in terms of their value for predicting mudrock durability. It is newly proposed that style of breakdown provides guidance for predicting the mechanical properties and that simple index tests can supplant relatively expensive and time-consuming undisturbed sampling and testing, even where this is possible. This approach has potential for use in the prediction of fracture formation owing to changes in stress conditions and pore water pressure.
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A surge of interest in the geomechanical and petrophysical properties of mudrocks (shales) has taken place in recent years following the development of a shale gas industry in the United States and elsewhere, and with the prospect of similar developments in the UK. Also, these rocks are of particular importance in excavation and construction geotechnics and other rock engineering applications, such as underground natural gas storage, carbon dioxide disposal and radioactive waste storage. They may greatly influence the stability of natural and engineered slopes. Mudrocks, which make up almost three-quarters of all the sedimentary rocks on Earth, therefore impact on many areas of applied geoscience.
This volume focuses on the mechanical behaviour and various physical properties of mudrocks. The 15 chapters are grouped into three themes: (i) physical properties such as porosity, permeability, fluid flow through cracks, strength and geotechnical behaviour; (ii) mineralogy and microstructure, which control geomechanical behaviour; and (iii) fracture, both in laboratory studies and in the field.