Study of subcritical crack growth of rocks and threshold values in different environments

Subcritical crack growth is one of the main causes of time-dependent behavior in rocks. Applied the constant displacement relaxation method, subcritical crack growth in specimens made of marble and granite which were in dry and water-saturated environments was studied in double torsion test. The relations of the stress intensity factor K1 versus the subcritical crack growth velocity V were obtained under the two different environments. The behavior of subcritical crack growth was analyzed. The threshold values of subcritical crack growth in rocks were obtained under the two different environments-dry environment: marble K0=1.365, granite K0=2.305; water-saturated environment: marble K0=1.118, granite K0=1.490. The results showed: the relations between lgK1 and lgV accorded with linear rules; but it were discrete because of inhomogenous mineral composition, etc, it was more discrete under water-saturated environment; water can accelerate the subcritical crack growth; the effect degree was different in different rocks; the threshold values were reduced by water; the reduction was different in different rocks.