A Study on the Point Load Test of Irregular Lump Rocks

The point load test of irregular lump rocks is a very promising and simple method for obtaining the indexes and the compresstve and tensile strength of rock. In this paper, the rocks of five typical shapes (approximate spheroid, ellipsoid, rectangular parallelepiped, prism and tetrahedroid) are calculated and analyzed by the finite element method. The distributive laws of stress of irregular lump rocks under the pressure of point loads are discussed. The stress distribution in all of the lumps are similar, except for the tetrahedroid which is very rare. These tests have led to an important conclusion that the shape of irregular lump rocks has not a significant influence oa stress distribution.Six strength indexes are defined. In situ, a large number of irregular lumps of various sizes of four types rocks (limestone, sandstone, shale and coal) are examined. By the method of statistical analysis, the optimal strength index and its stable region are determined. The comparison of the strength indexes of the tests with the index of the conventional uniaxial compressive strength, tensile strength and the strength index suggested by E.Broch about rock core subjected to radial point loads demonstrates htat there exists the possibility for this test to take ISVA as the strength index of rock.