Experimental investigation on grouting in 3D orthogonal fracture network with flowing water under coupled thermal-hydro-mechanical conditions

Underground engineering geological conditions are complex and concealed. Grouting technology utilizes the characteristics of fractures in rock masses to effectively seal major water-conducting fractures, achieving the objectives of water control and isolation. This paper presents an experimental investigation into the thermal-hydro-mechanic coupled effects on grout diffusion within a 3D orthogonal fracture network. The influence of hydrodynamic conditions, ambient temperature, and properties of different grouting conditions on both sealing efficiency and grout diffusion in a water-bearing fracture network is systematically analyzed. When injecting the same volume of grout at a fixed temperature, sealing efficiency remains high across all temperature levels under low-flow conditions. However, as the flow rate increases, relative sealing efficiency becomes more favorable at lower temperature. In main/bottom view, the diffusion pattern is divided into (I) pressure-driven diffusion phase/fracture-filling diffusion phase, (II) combined diffusion phase driven by gravity and downstream flow/near-circular diffusion phase, and (III) current-driven diffusion/downstream-oriented circular diffusion. This study introduces the concept of “grout pile effect”, which describes the overall sand-pile-like diffusion pattern of grout, exhibiting an angle of repose similar to that of granular materials. Sealing frequently occurs at critical “throat sealing” positions, providing advantageous position for field grouting operations. These findings provide valuable insights for more accurate prediction of grouting performance and more effective prevention and control of water inrush in practical engineering.