Geotechnical characteristics of the Borrowdale Volcanic Group

AS part of its investigations in the Longlands Farm area near Sellafield, w est Cumbria, Nirex has generated a database of geotechnical information on the Borrowdale Volcanic Group rocks. Information has been obtained to depth s of over 1000 m. The database was originally created to provide input to p ost-closure performance assessment studies for a potential radioactive wast e repository. However, the information gathered is of generic value in unde rstanding both the geotechnical characteristics of these deep rock units an d the techniques available for their characterization. Information on the l ithological characteristics of the rock units, the spatial properties of di scontinuities, rock material properties, in situ stresses and rock mass pro perties has been collected from investigations including surface mapping, b orehole core logging, borehole testing and geophysical surveys. The informa tion has been compiled into a series of data sheets summarizing the charact eristics of the identified rock units as a basis for subsequent modelling. Variations in rock mass properties, expressed as rock mass ratings, have be en mapped in three dimensions using information obtained from boreholes and from regional geophysical surveys. The paper describes the studies underta ken and presents a summary of the results obtained.