Compressive behaviour of lump-grout material under lateral confinement: Laboratory tests

The lump-grout (LG) material consisted of coarse lumps and pumpable grout has been developed as an alternative infill material to cementitious grout (CG) material in secondary standing support for underground mines. This paper aims to further explore the compressive behaviour of the LG material under variable lateral confinements. A total of 30 LG specimens and 15 CG specimens, either under the active confinement via a Hoek cell or the passive confinement with a fibre-reinforced polymer (FRP) jacket, were prepared and tested. The main test variables included the confining pressure (i.e., 0, 2, 4, 6, 8, 12, 16 MPa) applied by a Hoek cell and the FRP jackets made of variable FRP composites (i.e., CFRP, GFRP and UHMWPE FRP). Test results demonstrated that both the compressive strength and the axial deformation of the LG material were obviously enhanced attributed to effective lateral confinement. The stress path independence assumption was also verified from this research, which provided a feasible access to build the relationship between the active- and passive confinement to the LG material. The in-depth comparison with the CG material, the LG material is much suitable as the infill material for the standing support, in terms of its cost-effectiveness and environmentally friendly.