3.2.1.2 Irregular Lump
Numerous authors have investigated the loading of irregular lump samples to measure their strengths. The method involves testing a sample between two loading implements, which can be in the form of points or flat surfaces. The sample is then subjected to an increasing load until breakage occurs.
Work conducted by Hiramatsu and Oka [1966] compared the point loading of spherical specimens to irregular lump samples using a range of materials. They concluded that the tensile strength could be approximated to 0.9 times the critical load and can be represented by the following equation:-
Where F0 is the critical load and 2a is the distance between the loading surfaces.
Broch [1972] gives a detailed review of the work previously carried out and compared the point load test to that of the uniaxial compression test (UCS). He concluded that the point test could be considered a suitable replacement to the UCS method. Other benefits to the point load of irregular lump samples was the need for little sample preparation and the possible portability of the method due to the reduced forces required to induce failure.
Bieniawski [1974] compared the results of irregular lump loading to that of axially and diametral loading of core samples and concluded that the axial type test was the most suitable and that to avoid confusion this type of test be used in preference to other tests.