Shear Strength and Permeability Evolution during Shear-Holding in Single Rock Fracture

Abstract

This paper presents direct shear test results for single jointed granite and mortar specimens to investigate effects of long-term load holding on mechanical and hydrological properties of rock joints. From the test results, it was confirmed that shear strength increased and permeability decreased for mortar specimens through three days load holding. For granite specimens, however, significant change was not confirmed on mechanical and hydrological properties through up to twenty days load holding due to smallness of confining pressure compared with the strength of granite and shortness of load holding. Relationship between the time of shear holding (th) and the growth of shear strength during shear holding (Δτ) was examined for mortar specimens. When tn was shorter than 106sec, Δτ increased in proportional to the logarithm of th as Dieterich's log-linear model, which explains the time-dependency of Δτ as increase of contact area of fracture surface due to asperity creep. When th was about 106sec, however, Δτ was larger than the value predicted by the Dieterich's log-linear model. This result implies growth of adhesion driven by chemical action at contact area of fracture surface such as pressure solution and precipitation.