Research Status and Prospect of Polyurethane Used in Soil Pretreatment for Trenchless Repair of Drainage Pipelines

Polyurethane (PU) soil pretreatment in non-excavation sewer rehabilitation faces compatibility conflicts between its hydrophobic properties and water-saturated soil environments in high-water-content, weak strata. This leads to reduced consolidation efficiency, weakened interfacial bonding, and long-term performance degradation, limiting the reliable application of this technology. Based on this, this paper systematically reviews research progress on polyurethane for soil pretreatment. First, its performance characteristics are outlined. Subsequently, the current state of research is systematically introduced, focusing on strategies to enhance PU reinforcement strength and stability, as well as optimize the interface transition zone (ITZ) structure. These approaches include material modification (e.g., inorganic/silane composites, molecular chain regulation) and process innovation (e.g., grouting parameter optimization, curing process design), seeking breakthroughs through multifunctional composite modification and refined process control. Finally, this article points out that future development should focus on the research and development of low-cost, high-performance polyurethane materials, and strengthen the research on their durability in complex environments, thereby promoting the further development of polyurethane materials in the field of trenchless repair.