This posting may be a bit late to be useful, however:
Design the excavation as a rock cutting, with measures such as sprayed concrete, meshing, bolting or anchoring as appropriate, in order to maintain the self-supporting nature of the rock.
If you don't build a retaining wall then you don't...
Look at British Geological Survey sites (BGS have a global seismology and geomagnetism group based in Edinburgh)
e.g. for a study of seismicity and earthquake hazard in the UK including North Sea
http://www.gsrg.nmh.ac.uk/hazard/hazuk.htm
also...
Seek help from the tunnel lining manufacturers - ask them for names of projects involving their products and references to published papers.
Try for example sending an enquiry to the Charcon Tunnels division of Tarmac Precast - the email address is on their site at http://www.charcon.co.uk/
In a triaxial test the hydraulic pressure in the cell is the confining pressure sigma 3.
Sigma 2 is the same as sigma 3 in atriaxial cell.
Sigma 1 is increased above sigma 3 by applying a 'deviator' stress in the vertical (axial) direction by loading the top of the sample.
Sigma 1 - Sigma 3 is...
