Experimental study of the effect of fracture size on closure behavior of a tensile fracture under normal stress

Tensile fractures that measured from 37.5 mm×37.5 mm to 260 mm×260 mm were created in sandstone perpendicular to the bedding plane by intending steel wedges, and closure of these fractures under normal stresses of up to 10 MPa was measured in the laboratory to investigate the effect of fracture size on closure behavior. Prior to the tests, the aperture distributions were determined by measuring the topography of the upper and lower surfaces using a non-contact surface profile measurement system with a laser profilometer, and the power spectral densities (PSDs) of the initial aperture and the surface heights were calculated by using a standard fast Fourier transform (FFT). The experimental results showed that at a given normal stress, closure significantly increases with an increase in fracture size. However, the relation between normal stress and closure, normalized by the standard deviation (SD) of the initial aperture, is almost independent of the fracture size, since the SD of the initial aperture also increases with fracture size. Thus, the size effect on the closure of a fracture under normal stress is governed by that on the SD of the initial aperture.