Full-face water-rich gravel stratum is a large challenge during tunnel excavation with earth pressure balance shields (EPBs) because of accidents such as water spewing from the screw conveyor and ground collapse. Slurry and polymer have been used as conditioning agents to avoid such problems and thus ensure a successful tunneling. However, limited improvement of sandy gravel was achieved when traditional soil conditioner were applied. This study proposes a new conditioner (modified slurry) consisting of bentonite slurry, viscosity modifier, sodium silicate and polymer, which will enhance the properties of sand gravel stratum. Low reaction time, high apparent viscosity, good plastic behavior and low permeability were employed for investigating the optimum ratio of the ingredients. The proposed modified slurry has a good performance in conditioning sandy gravel soils and can be the reference for EPBs’ excavation in highly permeable, non-adhesive coarse-grained soil stratum.

Energy storage spring is an important component of the circuit breaker’s spring operating mechanism. A three-dimensional model of the opening spring and closing spring of the 126kV circuit breaker was established through COMSOL, and the stress and strain distributions in the stored energy state and the non-stored energy state were obtained through finite element calculation. The results show that the stress and strain of the inner ring of the spring is significantly greater than that of the outer ring, the maximum stress of the spring is lower than the yield strength of the spring steel, and the stress level meets the requirements. Based on the stress calculation results, the fatigue life analysis is carried out through the S-N curve. The minimum fatigue life cycles of the closing spring and the opening spring are 2×10 ⁴ times and 2×10 ⁵ times, respectively, which meet the life requirements of the circuit breaker operating mechanism.

The detent is an important component that affects the reliability of the spring operating mechanism of the circuit breaker. Three-dimensional modeling of opening detent, closing detent, energy storage retention detent and closing retention detent is carried out based on COMSOL. The stress conditions of them under the two working conditions of closing spring energy storage state and closing holding state are analyzed, and the corresponding stress and strain distributions are obtained through finite element calculation. The fatigue life analysis based on the S-N curve shows that the closing detents, opening detents and energy storage retention detents will not suffer fatigue damage, and the minimum fatigue life of the closing retention detents is 1.74×10 ⁴ times, which meets the requirements of mechanical life of circuit breaker operating mechanism.

A sealing grease plays a crucial role in the sealing of shield tails. Its pumpability and pressure sealing resistant sealing performance are greatly affected by the fiber content. In this study, discrete element method models were used to simulate the pressure-resistant tests of sealing grease in order to investigate the influence of viscosity grade and fiber’s aspect ratio on the optimum fiber content of sealing grease. Meanwhile, the rationality of the optimum fiber number determined based on the sealing performance was verified with the unbalanced force and fiber area proportion obtained in the simulation, of which the variation curves with the increasing fiber number were practically identical. The simulation results elucidated that the viscosity of grease had little effect on the optimum fiber content for sealing grease. However, the increase in viscosity can improve the sealing effect, and increasing the fiber’s aspect ratio can reduce the fiber number to reach a specific seal state. Based on the analysis of the total number of fiber spheres for the models with different fiber’s respect ratios, it can be concluded that the sealing grease sample made of the same fiber material and quality can reach the same seal state and seal effect, independent on fiber’s aspect ratio.