Clogging in earth pressure balance (EPB) shield tunnelling through highly cohesive strata critically undermines construction efficiency. Conventional foam agents exhibit limited conditioning effectiveness, even with increased dosage. This study developed a dispersed foam agent by combining anionic surfactant (AES) with nonionic dispersant (HDT). The effects of air pressure (0–2 bar) and HDT content (0–10%) on macro-meso characteristics of foam and adhesion characteristics of conditioned soil were quantified through an evolutionary mechanism investigation of the bubble size distribution of foam, half-life measurements, and mechanical tests on conditioned soils. Results demonstrated that the influence of HDT content on foam exhibited pressure-dependent behavior. Under 0 bar within 0–10 min, HDT increased the proportion of small bubbles while marginally reducing the mean radii. Although HDT accelerated the degradation of small bubbles, it extended the foam half-life. Conversely, under 1 or 2 bar, HDT demonstrated opposite effects on these parameters. The cohesion of conditioned clays was reduced to 1.8–4.3 kPa, and adhesion amounts decreased to 10–15 g, significantly mitigating clogging risks. The optimal injection ratio of dispersed foam was determined for different pressures and clays. Engineering application in an EPB shield tunnelling section of Jinan Metro successfully resolved clogging issues, demonstrating the effectiveness of dispersed foam agent.

In urban underground construction, Earth Pressure Balance (EPB) tunneling faces complex geological uncertainties and dynamic operational risks. Traditional safety management approaches often struggle under such conditions. This paper proposes an integrated safety resilience assessment framework for EPB tunneling that combines an entropy-weighted TOPSIS method, the Analytic Network Process (ANP), and an extension cloud model to capture interdependencies and uncertainties. A hierarchical indicator system with four primary dimensions (stability, redundancy, efficiency, and fitness) is constructed. The entropy-TOPSIS algorithm provides objective initial weights and scenario ranking, while ANP models the feedback relationships among criteria. The extension cloud model quantifies fuzziness in expert judgments and converts qualitative assessments into probabilistic resilience ratings. The methodology is applied to a case study of the EPB shield tunnel section of Jinan Metro Line 6 (China). The section’s resilience is classified as a medium level, which agrees with expert evaluation. The results demonstrate that the proposed approach yields accurate and robust safety resilience evaluations, supporting data-driven decision-making. This framework offers a quantitative tool for resilience-based safety management of shield tunneling projects, providing guidance for shifting from traditional risk control toward a resilience-enhancement strategy.

Given the prevalent issue of earth pressure balance shield tunneling encountering spewing in water-rich sandy strata, a dedicated soil discharge model test system was devised. Through comprehensive tests on both unconditioned and conditioned soil under submerged conditions, this system unveiled the temporal distribution patterns of water pressure throughout the soil discharge and discharge phases. The test results show that in the case of unconditioned soil, once the water pressure within the soil chamber (Pt) surpasses 100 kPa, significant fluctuations occur upon opening the soil outlet, leading to a heightened risk of spewing. The severity of spewing can be gauged by analyzing both the average water pressure at the measurement point and the coefficient of variation in water pressure. The water pressure and water flow in the soil chamber have a great influence on the water pressure distribution in the soil discharge process. Changing the spiral speed n and soil discharge opening ratio ξ cannot restrain the spewing. For conditioned soil, individual agents like foaming agent and bentonite are prone to being washed away under high water pressure. Bentonite combined with a high molecular polymer can effectively seal the dominant flow channels within the sandy soil gap. Through the use of a shield tunnel within the Nanchang Metro, the soil conditioning system underwent renovation, introducing a spewing prevention technology employing multiple pipeline quantitative injections. This conditioning approach effectively mitigated spewing issues and enhanced soil discharge efficiency, offering valuable insights for similar engineering endeavors.