Theoretical and Experimental Validation of Point Load Strength Test for Irregular Lumps

The possibility of testing irregular lumps under the point load strength test (PLST) was investigated theoretically and experimentally. In particular, a new analytical solution for stress distribution within a sphere under the diametral PLST was obtained by incorporating the classical solution with the Hertz contact stress. The stress distribution within the spheres was then compared with those of cylinders under the axial and diametral PLST, which were calculated by using the analytical solutions derived by the authors in 1999 and 2001, respectively. Numerical results showed that, if the dimensions of the spheres and cylinders are comparable, the stress distributions, especially the tensile stress distributions along the axis of loading within spheres and cylinders, are similar, both in terms of the magnitude and the pattern of stress distribution. The point load strength index was approximately the same for all three kinds of specimens. In addition, over 100 plaster specimens with different shapes (spheres, cylinders, hexagons, and cubes), three sizes (50, 60, and 75 mm), and two different strengths were tested using the axial or diametral PLST. The theoretical predictions agreed well with the experimental results. Thus, first by means of theoretical analysis, it was concluded that the point load strength index is not sensitive to the exact shape of the specimen, and secondly, it was further verified by experiments on plaster specimens.