Karst is an unfavorable geology that is very undesirable in tunnel construction. It is extremely risky due to the complexity and fuzziness of shield excavation in karst strata. To reduce the construction risk of shield tunneling in karst strata, a risk assessment method based on cloud model and fuzzy analytic hierarchy process (FAHP) is proposed. A risk assessment index system is established, including four first‐level indices of karst geological conditions, hydrogeological conditions, tunnel design, and shield construction, as well as seventeen second‐level indices. Fuzzy analytic hierarchy process is used to determine the evaluation indices weights. The numerical characteristics of each index and the risk cloud diagram are obtained via the backward cloud generator and forward cloud generator, respectively. The certainty degrees of the assessment indices corresponding to each risk level are calculated, and the final risk level is determined based on the comparison of the risk cloud diagram and the principle of maximum certainty. The proposed model is applied to the risk analysis and calculation of shield tunnel engineering, and the risk assessment results indicate that the comprehensive risk level of shield tunnel construction in karst strata is level II, which is consistent with the actual project. It demonstrates that the proposed method can provide a reference for the risk assessment of shield tunnels construction in karst strata.

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.

Rock mass blasting is a complex process that involves the coupling of both discontinuous and continuous media. This paper aims to reveal the dynamic failure process between adjacent boreholes under an elliptical bipolar linear charge structure using the SPH‐FEM (smooth particle hydrodynamics and finite‐element method) coupling algorithm numerical simulation method. The numerical simulation results are compared with the existing experimental results, which proves the rationality of the algorithm. According to the numerical simulation results, the shaped jet will first shock the hole wall and form a stress concentration zone that will guide the formation of cracks during the stress wave propagation process. In the case of double‐hole blast loading, there is a tendency for cracks coalescence to develop between adjacent boreholes due to the superposition of stresses between the double holes and the increase in damage and plastic strain. The best blasting results will be achieved with this structure when the distance between adjacent holes is 110 cm. Finally, the superiority of elliptical bipolar linear blasting in engineering blasting was verified through field experiments. The results of this study provide a reference for subsequent applications of elliptical bipolar structures in the field of rock blasting.

The construction risk of deep foundation pit (DFP) engineering is high, and accidents occur frequently. It is necessary to evaluate the risk of deep foundation pits before construction. At present, although there are many risk assessment methods, there is not one with strong applicability and high accuracy. Based on expert scoring, this paper analyses the risk from two aspects (the severity of consequences and the probability of occurrence), divides the severity of the consequences into five indexes, calculates the risk by using the analytic hierarchy process (AHP), and sets the expert weight index so that the subjective expert scoring result can obtain the best possible objective calculation result. In addition, this paper uses the membership function from fuzzy mathematics to establish the level of risk and optimize the evaluation criteria of risk events. An engineering example is introduced, and the result of the risk assessment shows that the evaluation result R (risk value) obtained by the optimized risk assessment method in this paper is 7.9 and that the level of risk is grade III. The risk assessment method proposed in this paper has strong applicability and can obtain more accurate evaluation results. This method can provide a reference for the risk assessment of deep foundation pit engineering.