Experimental Study On Tensile Strength Of Maokou Limestone Based On Brazilian Test

With the development of the national economy, the development and utilization of underground space are becoming key areas in human studies. Tensile strength is one of the important parameters of rock strength properties, as we know, the compressive strength of the rock is larger the tensile strength. Most of engineering rock mass destroyed from the tensile area, Maokou limestone is widely encountered in the southern mining engineering medium, therefore, to determine the peak tensile strength Maokou mouth limestone has important significance.We do Brazilian test under different loading condition, loading rate and thickness-to-diameter ratios, then discussed the influence of these factors.Base on Mohr theory, under different confining pressure, triaxial compressive strength of Maokou limestone tested by MTS 815 testing machine and we get the basic mechanical parameters. Through the experimental study, the results shows that:(1) Under different loading condition, Tensile strength decreased and present linear relation with the increase of thickness size. Tensile strength increased and present linear relation with the increase of loading rate. Under low loading rate, the specimen occurred stress-line drop phenomenon, with the increase of loading rate, stress-line drop phenomenon disappeared. The load contact condition has an important influence on the tensile strength of rock, because of less stress concentration, the tensile strength of arc load is 1.59, 2.52 times larger than plate loading and steel loading. Under different loading conditions, the failure modes of specimens are different, the disc broken into two parts in plate loading, the failure of disc formed a main crack into one or two secondary crack growth in steel loading, many secondary crack occurred under principal stress direction in arc loading. Compared the above test results, recommend to arc load as the best loading way to test rock tensile strength.(2) With the increase of confining pressure, triaxial compressive strength increase and present linear relation.Expansion rate increase with the confining pressure increasing, when confining pressure is 12 MPa, rock samples is from brittle transiting to ductile, when confining pressure rise to 17 MPa, rock samples turn to ductile.Through triaxial compression test. Maokou limestone’s cohesion is 22.9 MPa, internal friction Angle is 44.7 °.(3)Discussed the influence of different factors through FLAC3 D, we find that the first fracture starting point is at the center of the disc ends, which proved the disc is broke form the center.The more close to the ends,the higher of the horizontal stress. The larger of the thickness-to-diameter ratios,the lower of the horizontal stress of the central point of the specimens, Tensile strength increased with the increase of loading rate, which matched physical test well.Finally, Tensile strength correction formula are presented, eliminated the influence of the thick diameter ratio and loading rate on rock tensile strength,the validity of the modified formula is verified.