A Large Scale In-Situ Compression Test On A 1.5m Coal Cube

Results of a large scale compression test in situ are the subject of discussion. A cube of coal having an edge length of 1.5 meters was subjected to uniaxial compression tests in situ. At the same time both load and deformation were controlled. Deformations were measured on 60 short measurement bases, each 23 cm in length. The bases were uniformly distributed on the side surface of the cube, forming five horizontal rows and twelve columns on the development of the surface. Readings were taken from each gauge for each level of loading which was increased step by step. Due to heterogeneity of the rock, readings showed scatter. Scattered data were approximated by a plane, using the least squares method for each row separately and for the entire population of bases. Orientation of the planes are analyzed. The geometrical measure of the bending moment is introduced. It shows that the magnitude of the bending moment and the bending plane differed from row to row, thus implying that the cube was not only bent but twisted as well. This complex behaviour of the coal cube is apparently caused by its heterogeneity and vertical anisotropy. The results constitute a contribution to the verification of existing design criteria on the stability of mining pillars.