Physical simulation of the influence of the original rock strength on the compaction characteristics of caving rock in longwall goaf

The compaction characteristics of broken rock in a caving zone have a significant impact on the movement law of overburden and the prediction of surface subsidence. The mechanical properties of the broken rock were clearly affected by the original rock strength of the roof. Based on the similarity theory, the ‘quartz sand-gypsum-lime-water’ mixed material was used to make similar samples of original rocks with different strengths, and the compaction mechanical behaviour of broken loose rock masses with different original rock strengths was studied. The results show that (i) the greater the original rock strength of broken rock, the shorter the initial compaction stage, the earlier the transition and stable compaction stages and the lower the degree of compaction; (ii) the initial deformation modulus and ultimate axial strain had a linear relationship with the original strength of the broken rock; and (iii) under different axial pressures, the deformation modulus increased with the increasing original rock strength of the broken rock. The tangent modulus and axial stress change approximately linearly, the secant modulus and stress change linearly, and the tangent modulus and secant modulus exhibit an exponential/hyperbolic relationship with the strain. The research results have high engineering application value for using numerical method to predict the mechanical behaviour of roof rock mass with different strength in coal mining and analysing the surface subsidence.