Progress with thermomechanical investigations of the Stripa site

The Stripa mine in Sweden has provided an unusual opportunity to investigate the thermomechanical behavior of a granitic rock mass and the effect on such behavior of the discontinuities that are a persistent feature. Experiments to simulate the thermal effects of burying radioactive wastes have been carried out at a depth of about 340m. All of the thousands of underground measurements of temperatures, displacements, and stresses in the rock, recorded continuously over this period, have been made available on digital tape and in hard copy. This paper presents some results of recent investigations. Although temperature fields predicted by calculations based on linear heat conduction compare well with measured field data, evidence for some convective heat transfer has been found. Measured values of displacements have been significantly less than those predicted by calculations. Evidence that these displacements are diminished by fractures in the granite has been found. A program of laboratory investigations has been started to measure coefficients of thermal expansion and elastic moduli for Stripa granite. USAP (Underground Structural Analysis Program) is a unique finite element program that has been developed specifically for the analysis of underground structures; it has the potential to be used effectively in general problems associated with the underground storage of nuclear waste