| This paper applied theoretical analysis, laboratory experiments and computer programming to investigate the relations between point load strength, uniaxial compressive strength and uniaxial tension strength.According to the theory of stress distribution in a semi-infinite body, the axial stress of point load test was analyzed. Then combined with the strength theory of rock failure, the fundamental causes of rocks failure under point loading were discussed. Rock sample surface contacts with indenters under the interaction of compressive stress and tensile stress, tensile strain reaches its limit, and then tensile failure forms firstly near the indenters. After undergoing partial failure, the stress concentration occurs rapidly, and is transferred to the deep part of rock sample by cracks, when the two cracks get across, rock sample will fail completely. Point load strength is the comprehensive reflection of uniaxial compressive strength and tension strength.Using self-designed point load tester and RMT-150B rock mechanics testing system to test point load strength, uniaxial compressive strength and tension strength of the six kinds of rocks common in coal seams. According to test results, the influence of indentation depth on point load strength was analyzed; a new calculation method without considering the indentation depth was put forward; the linear model and power function model were built.Empirical formulas for cylinder rock sample were fitted by Mathematica software and error analysis, a new program of conversion of point load strength into compressive and tensile strength was developed.The method of converting point load strength into uniaxial compressive strength and tension strength were verified. The rock mechanics parameters can be achieved faster, cheaper and accurately by the high accuracy method. Finally, it can provide important basis for rock mass classification of seams. |
PDF Full Text Request