Standing support incorporating FRP and high water-content material for underground space

The integrity and stability of underground space mainly depend upon the coordination of primary and secondary support system. This paper presents a novel secondary standing support system, termed fibre-reinforced polymer (FRP)-confined high-water content cementitious grout material column (FCCM), being an alternative structural form for underground space. The attractive feature of the FCCM is its exterior container made of FRP composite with high strength-to-weight ratio and high corrosion resistance. A total of 30 FCCM specimens were prepared and tested to demonstrate its expected structural behaviour under compression. The critical parameters covered the type and the thickness of FRP tube as well as the strength of infill material. Test results verified that the cementitious grout material in the FCCM was effectively confined by the exterior FRP tube, resulting in the significant enhancement of load carrying capacity and deformation ability. The test results also indicated that the water expulsion of confined cementitious grout material may be the other reason for the superior compressive behaviour of FCCMs. The strain hardening FCCM with large axial deformation is particularly suitable for these underground spaces where the integrity and corrosion are the main concerns.