The effects of strain rate and saturation on a micro-cracked marble

It is well known rock masses contain several types of weakness planes varying from micro-fissure to fault in size. The fracture frequency, degree of saturation and time are the basic rock parameters affecting its behaviour. However, in most cases, it is practically difficult to test heavily fractured rock in laboratory environment. In this study, the effects of micro cracks, strain rate and water saturation on strength are discussed using a small-scale physical experiments. It is attempted to detach the grain boundaries of coarse-grained rock specimens of the Muǧla marble by thermal treatment that would serve as a small-scale physical simulation of fractures in rock masses and enable a discussion of the variations in time dependent mechanical behaviour. An experimental study was conducted on marble specimens induced thermally by micro-cracks in different frequencies. The thermal treatment periods being 24 h in inert atmospheric condition were varied for each test specimen except categories A and G. Effective porosity increased up to 2.4% after the last thermal cycle of category F. Then conventional compression tests with different strain rates were carried out using a servo-controlled testing machine on both dry and saturated specimens. It is concluded that both lowering strain rates and increasing porosity related with thermally induced micro cracks have important effects on strength and failure path. The progressive failure entirely occurs along the grain boundaries fissured by cyclical treatment and inter-granular deformation depends upon degree of thermal influence. The small-scaled laboratory model enabled to demonstrate that parameters such as joint frequency, time and saturation have a significant effect on mechanical behaviour of rock masses.