Fracture toughness was measured for a range of rock materials as a function of temperature between ambient temperature and 150°C. Measurements were made along all three principal crack orientations for the transversely isotropic Mancos shale and in single orientations for the more isotropic Darley Dale sandstone, Indiana limestone and Lanhelin granite. Fracture toughness was measured using a modified short-rod method with the sample and loading equipment enclosed within an elevated temperature chamber. A slight increase in KIc was observed in Lanhelin granite with increasing temperatures up to 54°C, before a steady decrease at higher temperatures. For the sandstone and limestone, little change was observed in KIc over the studied temperature range. In measurements on Mancos shale at elevated temperatures. Fracture toughness was seen to increase slightly with increasing temperature in the arrester orientation over this range, while remaining constant in the other two orientations. These observations can be explained in terms of the development of thermally induced microfractures parallel to the bedding planes in this material. A bimodal distribution of KIc values in the short-transverse orientation was not observed, as it has been for previously published measurements at ambient conditions.
Figures & Tables
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.