Stability Analysis Method for Initial Support Structure of Tunnel in Swelling Loess

The stability of tunnel is greatly affected by the changes in volume and strength of swelling loess caused by humidification. Quantitative reflection of the influence of humidification on stability in mechanical model has important engineering significance for the design of support structures. Based on the fact that parameters related to swelling and strength are functions of water content, the water content was introduced into the classical surrounding rock–support model, and a safety factor was employed as the index of stability. Thus, a stability analysis framework of swelling loess tunnel was established by considering the swelling and softening of swelling loess. In an engineering case, the theoretical models presented in this paper were introduced to investigate the change rules of surrounding rock deformation and tunnel safety factor, as well as the sensitivity of the safety factor of tunneling in swelling loess. Analysis results showed that the change rules of surrounding rock response curves and safety factors obtained by the models were consistent with the actual situation, and the predicted maximum radial displacement of free face was close to the measured value. These indicate that the models are applicable to the stability analysis of initial support of swelling loess tunnel.