Experimental investigation of the failure of shield grease seals under the influence of environmental factors: A case study

Shield tail sealing is a critical problem that influences work safety during shield tunneling processes. In recent years, the number of accidents caused by the failure of shield grease during shield tunnel construction has gradually increased. Taking Foshan Metro Line 2 accident as the research background, this study adopts the indoor model test and Ansys computational fluid dynamics (CFD) to estimate the grease sealing performance under the influence of environmental factors. The results indicate that, temperature increase, seawater, and sand mixing will greatly weaken the sealing performance of grease. In fact, the grease viscosity has been greatly weakened due to environmental factors. Using the numerical model, a simulation study was carried out on the sealing performance of the shield tail under the conditions of different grease viscosity and length of grease cavity. Grease viscosity and length of grease cavity have a linear positive relationship with the time of initial water leakage. Finally, a grease sealing performance evaluation model is proposed. Based on the above research results, the environmental impact coefficient k can be determined. The results of this study can be beneficial in both the selection and evaluation of the shield tail grease.