为保证隧道洞口段的施工安全,在小寨山隧道洞口段塌方成因分析的基础上,利用尖点突变理论和PSO-ELM模型评价了隧道洞口段围岩的稳定性现状及其发展趋势;另外,根据洞口段塌方成因,对塌方处理措施进行了系统研究,并综合分析了处理效果,以评价各类处理措施的有效性。小寨山隧道洞口段塌方成因研究表明:洞口段的塌方成因主要是偏压原因和降雨原因,且突变分析过程的突变特征值均<0,得出隧道洞口段围岩处于不稳定状态,加之变形预测结果显示其后期变形仍将持续增加,进而隧道洞口段的稳定性趋于不利方向发展,有必要采取切实措施保证施工安全;同时,塌方处理措施应结合工程实际,先对各施工阶段和步骤进行针对性加固,再调整隧道支护所受的宏观应力状态,保证其受力平衡,且通过塌方处理,小寨山洞口段围岩变形处于可控范围内,验证了各类处理措施的有效性。

To ensure the construction safety of tunnel's entrance segment, the causes of collapse at the entrance segment of Xiaozhaishan Tunnel are analyzed. On such basis, the status and development trend of surrounding rock stability are assessed using the cusp catastrophe theory and PSO-ELM (Particle Swarm Optimization based Extreme Learning Machine) model. The collapse treatment measures are systematically studied, and the treatment effects are analyzed to evaluate the effectiveness of measures. Results demonstrated that the major causes of collapse are deviatoric pressure and rainfall. The catastrophe characteristic values in the process of catastrophe analysis are less than zero, indicating that the surrounding rock of entrance segment is in an unstable state. In addition, deformation prediction results suggest that the deformation would continue, which is unfavorable for the stability of the entrance segment. Collapse treatment measures should be comprehensive and systematic to maintain the deformation of surrounding rock within controllable range. The effectiveness of various treatment measures is verified. The research findings offer a new idea for the prevention and control of hazards at such entrance segment of tunnels. Moreover, the collapse treatment measures should be implemented according to the practice of actual project. Targeted reinforcement should be carried out on surrounding rock in each construction stage, and then the macroscopic stress state of the tunnel support should be adjusted to ensure the stress balance. After treatment, the deformation of surrounding rock in Xiaozhaishan tunnel entrance is within controllable range, which verifies the effectiveness of the treatment measures.