Tri‐axial compressive behavior of high‐water material for deep underground spaces

Abstract Attributed to its superior water‐to‐solid ratio and quick setting time, the high‐water material is widely adopted in underground spaces as a cost‐effective and environmentally friendly backfill material. To elucidate the bleeding mechanism of high‐water material under the high confining pressure, a total of 57 tubular specimens were prepared and tested, critical parameters of which included the water‐to‐solid ratio, curing time, and lateral confinement pressure. Test results showed that no obvious cracks were observed from the surface of confined high‐water material, which is different from that of unconfined high‐water material, which featured shear cracks. Moreover, the volume of these confined high‐water materials under compaction exhibited a continuous shrinkage associated with the water bleeding. The threshold values of the water bleeding are significantly affected by the water‐to‐solid ratio, followed by the confining pressure and curing time. When other parameters are constant, the higher confinement is requested for these specimens with a small water‐to‐solid ratio. Meanwhile, the mass of bleeding water increased with the lateral confinement, showing a quick increase at the initial stage. During the bleeding process, the free water stored in the pores was compacted, the evidence of which is the transformation of the hydration products (calcium aluminate hydrate) from its natural fibrous structure into the rod‐shaped or dense agglomerate structures. These research outcomes provide an in‐depth insight into the fundamental mechanics of the high‐water material under the high lateral confinement when it is used for underground spaces.