To further enrich the side-filling structure system of goaf-retaining roadways and explore the compression reaction mechanism of the composite in the support environment of underground mine roadways, this paper introduces a double-wall hollow composite pier structure (FPRSC structure) that is composed of the fiber-reinforced polymer (FRP) composite and polyvinyl chloride plastic (PVC) as restraint materials and the infill material featured with a high water-to-powder ratio. A total of 16 circular specimens with a diameter and height of 100 mm were tested to explore the axial performance of the combined support structure. The main control variables in the present research included the water-to-cement ratio of the high-water material (e.g., 2:1, 3:1, and 4:1), the thickness of the FRP pipe (i.e., 6 mm and 3 mm), the inner diameter of the PVC pipe (i.e., 29 mm and 22 mm), as well as the thickness of the PVC pipe (1.5 mm and 5 mm). Test results showed that the high-water material was under triaxial stress due to the double-wall tube binding, and the bearing capacity of the composite was higher than that of the single material. Meanwhile, the FPRSC structure exhibited obvious strain-hardening characteristics when the infill material is under the combined constraints of double-wall hollow tubes. Moreover, the ratio of PVC-c, FRP-A, and high-water material with a water-cement ratio of 3:1 shows the best axial mechanical properties. The new composite pier structure with high toughness and strength has wide application prospects in the field of goaf retention in deep underground mines.
Keywords: composite support; fiber-reinforced polymer; high-water, fast-setting material; polyvinyl chloride plastic pipe; underground mine.