Optimizing Polyurethane Using As a Buffer Layer for Supporting Soft Rock Tunnels

Highway tunnels play a vital role in connecting cities and regions. Usually, lining structures with larger permissible deformation is considered a feasible solution to support soft rock tunnels. In this study, an optimized Polyurethane (PU) material was developed by conducting multiple laboratory trials, aiming to achieve a balance between low density, high compressive strength, high tensile strength, and low permeability. Such material is expected to serve as a buffer layer, facilitating stress release in the surrounding rocks and reducing support resistance. The optimized polyurethane is made up of 140:50:50:1.2:0.6:0.8:1.5:2.8 elements, which are composed of polyisocyanate, polyether triol, polyether tetrol, catalyst X, catalyst Y, foaming agent, chain extender, and foam stabilizer. The resulting polyurethane has a density of 145.4 kg/m3, solidifies in 58 s, exhibits a yield strength of 1.38 MPa, a tensile strength of 2.129 MPa, an elongation at break of 12.897 %, and a permeability coefficient of 1.24 & times; 10-5 cm/s. This work partially compensates for the limitations of foam concrete materials and provides an optimized support solution for large deformations in soft rock tunnels.