Geotechnical characteristics of the Borrowdale Volcanic Group

Abstract

SUMMARY As part of its investigations in the Longlands Farm area near Sellafield, west Cumbria, Nirex has generated a database of geotechnical information on the Borrowdale Volcanic Group rocks. Information has been obtained to depths of over 1000 m. The database was originally created to provide input to post-closure performance assessment studies for a potential radioactive waste repository. However, the information gathered is of generic value in understanding both the geotechnical characteristics of these deep rock units and the techniques available for their characterization. Information on the lithological characteristics of the rock units, the spatial properties of discontinuities, rock material properties, in situ stresses and rock mass properties has been collected from investigations including surface mapping, borehole core logging, borehole testing and geophysical surveys. The information has been compiled into a series of data sheets summarizing the characteristics of the identified rock units as a basis for subsequent modelling. Variations in rock mass properties, expressed as rock mass ratings, have been mapped in three dimensions using information obtained from boreholes and from regional geophysical surveys. The paper describes the studies undertaken and presents a summary of the results obtained.