PERMEABILITY CHANGES IN GRANITE WITH CRACK-GROWTH DURING IMMERSION INHOT-WATER

Permeability tests and observation of induced as well as inherent, cra cks have been carried out to quantitatively explain permeability chang es in granite taking place during a weathering test in terms of micro- structure by cracks. To this end, permeability tensors were estimated from observations of crack systems using the Replica Method and of the crack apertures with a scanning electron microscope. The following co nclusions were reached: the drastic increase in permeability around an immersion of 1000 d in 90 degrees C tl,ater could not be explained by the existence of a percolation threshold because all the specimens we re percolative in the sense that the traces of crack tensor were above the critical density for percolation. On the other hand SEM observati on revealed that, with immersion, crack apertures widened and their di stribution spread. Permeability estimated using the third (not the fir st) moment of observed apertures showed the increase in measurer: perm eability well. When evaluating the connectivity parameter lambda to gi ve a quantitative accordance between measured and estimated permeabili ty, it had a constant value as low as 0.17, irrespective of the immers ion period, in spite of the higher density of micro-cracks than the pe rcolation threshold. It can be said that, in considering the natural t hree-dimensional crack system, the third moment of physical apertures plays a more important role in predicting the permeability, and lambda is greatly affected by the spread of crack apertures. (C) 1998 Elsevi er Science Ltd. All rights reserved.