Hybrid roof standing supports in underground mining: concept and behaviour

ABSTRACT This paper presents a series of novel hybrid columns incorporating emerging materials, being the alternative to pumpable standing supports used in underground mines. The infill material of these hybrid columns is the cementitious grout material while the exterior containers are either made of polyvinyl chloride (PVC), fibre-reinforced polymer (FRP) composite, geogrid or the combination of each two materials. To investigate the mechanical response of these columns under the uniaxial compression loading, the systematic laboratory tests covering eight large-scale tubular columns were conducted and the test results showed that: (1) the strain constant behaviour of PVC-confined cementitious grout (PCC) column is mainly attributed to the relatively low confinement after the yielding of the PVC tube; (2) the high strength-to-weight ratio and linear tensile behaviour of FRP leads to the stress-hardening behaviour of FRP-confined cementitious grout (FCC) column and the enhanced compressive behaviour of FCC is mainly related to FRP thickness; (3) both the FRP-PVC confined cementitious grout (FPCC) columns and FRP-geogrid confined cementitious grout (FGCC) columns exhibited the superior compressive behaviour either in terms of the large axial deformation or the load carrying capacity, compared with the unconfined cementitious grout material (UCM) under uniaxial compression loading.