In this paper, the porous polyurethane grouting material was prepared by solution blending method. The nano- SiO₂ was used as the reinforcing phase to study the structure, morphology, mechanical properties, flame retardancy and thermal conductivity of the modified porous grouting- based material. The results show that: After the nano-SiO₂ doping, it is bonded with the polyurethane matrix, which enhances the pore wall strength of the porous grouting material, makes the morphological structure more complete, and improves the tensile strength and viscosity of the porous grouting material. The increase of the amount shows a trend of first increase and then decrease. The tensile strength and viscosity of the porous grouting material with nano-SiO₂ doping content of 0.8% both reach the maximum value. With the increase of nano-SiO₂ doping content, the maximum heat storage temperature of porous grouting material first decreased and then increased, the cooling rate increased first and then decreased, and the thermal conductivity continued to increase. The flame retardant test shows that the vertical burning time of the 0.8% nano- SiO₂ doped grouting material is the shortest 20.8 s, and the flame retardant performance is the best. From the perspective of various properties, the optimal doping

amount of nano-SiO₂ is 0.8%. Under this doping ratio, the maximum heat storage temperature of the porous grouting-based material is 143 ℃, the cooling rate is 1.75 ℃/min, and the thermal conductivity is 0.368 W/（m · K）, the vertical burning time is 20.8 s, and it has broad application prospects in tunnel fire protection applications.

solution blending method, polyurethane, porous grouting material, mechanical properties, flame retardant properties, thermal conductivity