Laboratory and distinct element analysis of the deformability behaviour of thin spray-on liners

Abstract

Thin spray on liners (TSL) are polymeric or cement-based products that have been used for underground rock support extensively. Although linear–elastic behaviour assumptions have been attempted during numerical modelling of TSLs by researchers, TSLs do not obey this behaviour in reality. The effect of curing time on the elastic material properties (Young's modulus, Poisson's ratio) and the compressive strength of flexible and rigid liners were studied. During the laboratory studies, samples from two different TSLs (flexible and relatively rigid) prepared in laboratory conditions with different curing times (2, 7, 14, 21 and 28 days) were tested based on the ASTM standards. It is concluded that an increase in curing time improves the compressive strength and modulus of the TSLs but decreases their deformation behaviours. The relationship between Young's modulus, the curing time and uniaxial compressive strength (UCS), and the curing time can be expressed with an exponential trend line for the rigid liner and a logarithmic trend line for the flexible liner, respectively. TSLs have no definitive constitutive behaviour revealed so far. In this study, distinct element modelling of TSLs on UCS test specimens were performed to be able to capture their true constitutive stress-strain behaviour under compression. Deformation behaviours of laboratory test specimens were simulated in a DEM code, PFC2D. Finally, a new scaling coefficient between macro and micro properties of PFC for deformability testing is calculated in order to decrease the laborious calibration process that one must go through in PFC modelling. If the strength and modulus of laboratory results of TSLs are known, their micro properties can be calculated using the presented scaling coefficient given in this study.