Because of the harsh environment around city subways and the typically poor geological conditions, it is often difficult to ensure the stability of a tunnel, which makes it prone to collapses and other accidents. The influence of multiple factors on tunnel stability was analyzed under the same geological conditions and environmental factors by using a three-dimensional numerical simulation. Taking into account the objective environment and manual operation and other factors, construction sequence, support closure time, and reinforcement area and parameters were chosen as the main factors affecting the tunnel stability. Finally, based on ground deformation, tunnel convergence deformation, and surrounding soil stress as evaluation indicators, a fuzzy analytic hierarchy process (FAHP)-gray correlation degree-technique for order performance by similarity to ideal solution (TOPSIS) model was established. It was found that the higher the relative closeness of the construction parameter combination, the greater the tunnel stability. The best combination of construction parameters was applied to the Tiantongyuan Station project of Beijing Metro Line 17. All geological conditions being equal, reasonable selection of construction parameters can ensure optimal tunnel construction stability, reduce construction risks, and support sustainable tunnel development. In addition, the FAHP-gray correlation degree-TOPSIS method achieved multi-index evaluation of tunnel stability, which provides practical guidance for the construction of similar projects.

The tunnel collapse is one of the most frequent and harmful geological hazards during the construction of highway rock tunnels. As for reducing the occurrence probability of tunnel collapse, a new dynamic risk assessment methodology for the tunnel collapse was established, which combines the Cloud model (CM), the Membership function, and the Bayesian network (BN). During the preparation phase, tunnel collapse risk factors are identified and an index system is constructed. Then, the proposed novel assessment method is used to evaluate the probability of tunnel collapse risk for on-site construction. The probability of tunnel collapse risk in the dynamic process of construction can provide real-time guidance for tunnel construction. Moreover, a typical case study of the Yutangxi tunnel is performed, which belongs to the Pu-Yan Highway Project (Fujian, China). The results show that the dynamic evaluation model is well validated and applied. The risk value of tunnel collapse in a construction cycle is predicted successfully, and on-site construction is guided to reduce the occurrence of tunnel collapse. Besides, it also proves the feasibility of the dynamic evaluation method and its application potential.

In the upper soft and lower hard composite strata, it is very difficult to sample the rock and test the mechanical properties of the samples. The study of the mechanical properties of similar material samples by artificial manufacture may enable an alternative method to solve this problem. Therefore, the feasibility of artificial sample preparation and the test of mechanical properties of rock samples in the composite strata become the key to solve the study of mechanical properties of the upper soft strata and the lower hard composite strata. For this purpose, the artificial composite samples composed of two kinds of materials with different strengths were prepared by using cement and kaolin as similar materials. Through the uniaxial compression test of artificial composite rock samples, the effects of the strength ratio of similar materials and the thickness ratio of higher strength materials on the mechanical properties of composite specimens were analyzed. The results of uniaxial compression test show that artificial similar materials could be used to simulate the composite rock samples which are difficult to sample. Without considering the structural interface effect, the greater the strength ratio of similar materials, the greater the impact on the overall strength of composite specimens. The change of volume proportion of high‐strength materials has a significant impact on the overall strength of composite specimens. Moreover, the numerical simulation and the experimental stress‐strain curves both show a similar trend, indicating that the deformation of the composite strata mainly occurs in the soft part. The research results can provide reference for the test and analysis of mechanical properties in similar complex strata with difficult sampling.