Plate-load testing as a method of assessing the In-situ strength properties of Western Canadian coal

Abstract

The prediction of the in-situ uniaxial compressive strength of coal from the results of plate-load tests was investigated. The observed behaviour of coal at two test sites indicated that the theory of the expansion of a spherical hole in an “elastic-brittle-plastic” material was applicable; this was reinforced by the fact that similar relations between the peak bearing capacity and the modulus of deformation were derived from both the theory and the field results. Interpreted in this manner, the uniaxial compressive strength, Q u and the ratio q/Q u , where q is the peak bearing capacity, for each test site were: Test site 1: Q u = 3·48 MN/m 2 (504 lb/in 2), q/Q u = 1·3 Test site 2: Q u = 8·45 MN/m 2 (1225 lb/in 2), q/Q u = 1·6 The key to interpreting plate-load tests in terms of uniaxial compressive strength lies in selecting the theory applicable to any set of results; this selection is assisted considerably by careful recording of the load-deflection curves and by close observation of the coal response and appearance both during and after failure.