To address the issues of excessive air volume and insufficient targeting effectiveness in traditional subway tunnel make-up air systems, a novel composite ventilation method was proposed. This approach integrated side-supply in the breathing zone with bottom-supply ventilation based on occupant evacuation behavior patterns, with the objective of investigating its effectiveness in controlling smoke dispersion in evacuation passages. A physical model of a metro tunnel section was constructed using numerical simulation. Comparative analysis was conducted on the distribution patterns of CO mass concentration, temperature, and visibility in evacuation pathways under four distinct ventilation conditions: natural air replenishment, breathing-zone lateral air supply, bottom air supply, and combined ventilation modes.The study found that natural make-up air had the worst effect on controlling fire smoke in the evacuation channel, with visibility, CO mass concentration, and temperature all failing to meet personnel evacuation requirements.Breathing zone side-feeding make-up air could control the CO mass concentration in the evacuation channel below 62 mg/m³, but the mixing of make-up air and smoke caused the average temperature in the evacuation channel to reach 227 ℃, which did not satisfy the requirements for safe personnel evacuation. For bottom make-up air, the average temperature in the evacuation channel exceeded 300 ℃, and the average CO mass concentration was 100 mg/m³, both higher than the safety parameters required for personnel evacuation. When the combined make-up air of breathing zone side-feeding and bottom-feeding was applied, with the air volume ratio of side-feeding to bottom-feeding being 6∶1 and the corresponding wind speeds being 1.8 m/s and 0.3 m/s respectively, the CO mass concentration in the evacuation channel was 34.6 mg/m³, the temperature was 59.2 ℃, and the visibility was 18.6 m—all meeting the standards for safe personnel evacuation. The combined make-up air method of side-feeding in the breathing zone and bottom-feeding can effectively control fire smoke in metro tunnel evacuation channels, providing a theoretical basis for precise make-up air design in underground spaces aimed at ensuring personnel safety.

In order to investigate the interaction mechanism between a shield machine and concrete pile foundations during cutting, the cutting-pile project at the Zhonghe Building group on the East Line of the Haizhu Bay Highway Tunnel was selected as the case study. Based on on-site exploration data, a finite-element model was employed to simulate the process of cutting a single pile with the disc cutter. The cutting forces on the disc cutter and the dynamic responses of both the soil and the pile were analyzed in detail. The simulation results showed that the pile's displacement response during the penetration phase was significantly greater than during the cutting phase, with the responses during penetration being concentrated mainly in the y and z directions. Moreover, the mean normal force acting on the disc cutter was higher in the penetration phase than in the cutting phase; when the strength contrast between adjacent media was large, the cutter force exhibited a pronounced discontinuity at their interface, thereby increasing the possibility of fatigue damage. The responses of the pile, the surrounding soil, and the cutter were thus characterized throughout the cutting process, and the findings were expected to provide valuable guidance for reducing safety risks in similar shield tunneling projects.

The deformation control mechanisms in underground caverns were investigated through systematic analysis of splitting phenomena within the surrounding rock's loosened zone. An elastic-brittle-plastic constitutive model was developed to formulate stress and deformation field expressions, enabling the derivation of a quantitative characterization for loosened zone dimensions. Stress relaxation mechanisms at rock mass discontinuities were analyzed, leading to systematic characterization of deformation and splitting processes within the loosened zone. Clear logical relationships between shear failure and splitting failure mechanisms were established, with a stress criterion for splitting failure in the loosened zone being proposed. Critical external load conditions were identified for four typical failure modes: shear failure, shear fragmentation, slab fracturing, and splitting in the maximum support pressure zone. Key findings revealed that radial unloading induced localized tensile stress fields in surrounding rock. Plastic shear deformation was confirmed as a prerequisite for internal rock mass splitting failure. A positive correlation was observed between modulus differences during loading-unloading cycles and splitting susceptibility. Comparative analysis demonstrated that the occurrence threshold for shear fragmentation significantly exceeded that of splitting failure, suggesting limited practical occurrence of shear fragmentation in engineering applications. These findings provide theoretical foundations for predicting and controlling surrounding rock stability in underground excavation projects.

To address the issue that the traditional arch cover method relies on the support of hard underlying bedrock and is difficult to function in soft and broken strata, the steel pipe pile column arch cover method, which can effectively exert the efficacy of the arch cover method in soft and broken strata, was proposed based on the Jinjiang Road Station project of Guiyang Rail Transit Line S1, and its construction mechanical characteristics were studied. The research results showed that steel pipe piles were added below the arch cover foundation in the steel pipe pile column arch cover method. On the one hand, the steel pipe piles served as the foundation of the arch cover to improve its bearing capacity; on the other hand, when the lower half section of the station was excavated, they played the role of “advanced support”, constrained the deformation of the sidewall rock mass, and ensured the overall stability of the main structure. Compared with the traditional arch cover method, the steel pipe pile column arch cover method could effectively reduce stratum settlement, and the steel pipe piles shared the surrounding rock pressure, thereby reducing the maximum and minimum principal stresses of the initial support structure system. During the construction of the steel pipe pile column arch cover method, the construction of the arch cover part was the key to the method. After the construction of the arch cover and the station's initial support was completed, the maximum structural stress was located in the junction area between the sidewall and the inverted arch, which was the focus of attention during construction. The steel pipe pile column arch cover method, which uses a support system combining four pilot tunnel double-sidewall drift excavation, steel-reinforced concrete arch cover, and steel pipe pile columns, was successfully applied in the Jinjiang Road Station of Guiyang Rail Transit Line S1. Relying on the efficient coordination of the divided pilot tunnel construction mode, special trolley mold casting, and synchronous pouring technology, the construction period was shortened by approximately 10 months compared with the traditional arch cover method, the operation efficiency was significantly improved, and the impact on urban traffic was reduced.