Study On Pressure Distribution Characteristics Of Shield Tail Sealing System Of Shield Machine

The shield machine is currently the most widely used tunneling equipment to deal with complex construction environments.It is developing towards large section and intelligent tunneling technology.In the process of shield tunneling,various problems and even accidents often occur due to complex construction environments and changeable working conditions.Shield tail sealing system is one of the important systems for shield machine to respond to construction risks such as groundwater leakage and grouting leakage,and to ensure the construction safety of shield machine.On the basis of the main study method,computational fluid dynamics(CFD)method of this paper,the pressure distribution and variation characteristics of shield tail sealing grease cavity under normal and leaking conditions are studied in this paper.The leakage criterion based on pressure monitoring is designed by applying the pressure distribution law of grease cavities under different conditions,the surrogate model technology and optimization algorithm are applied for optimization of shield tail sealing system.The study work of this paper has the following points:(1)Taking the shield tail seal system of earth pressure balance shield(EPB)as the research object,the pressure distribution change characteristics in the shield tail sealing grease cavity are studied.According to the relevant structural parameters of shield tunneling machine used in actual project and the actual shield tail sealing principle,a full-scale watershed model of shield tail sealing grease cavity is built.The grid model is established by hybrid grid scheme and verified by grid independence.The initial parameters and boundary conditions of the simulation model are set in accordance with the real situation.The pressure distribution and flow characteristics of the grease cavity under normal conditions are obtained by simulation calculation.And the rationality and feasibility of each model setting and simulation method are verified.(2)Based on the local full-scale model and multi-phase flow model,the pressure distribution law of grease cavity under normal and leakage conditions and the influence law of operating parameters on pressure distribution are analyzed.The full-scale model is simplified to a local model and verified to be feasible.The pressure distribution law of circumferential section of the grease cavity 2 is analyzed in detail,and the circumferential pressure distribution function model and spatial pressure distribution parameter set are established.The influence rules of different operating parameters on pressure distribution are studied,and suggestions on structural design and control scheme of grease injection are given.Leakage simulation model is designed,the flow characteristics and pressure changes of grease cavity at different times during the leakage process are analyzed,and the change rules of circumferential pressure of grease cavity under leakage state are studied in detail.The influence laws of grease injection pressure and mud intrusion characteristics on the pressure distribution of grease cavity and the sealing failure time are also analyzed.(4)The leak criterion design of pressure monitoring system and the optimization of shield tail seal system aiming at reducing the difference of pressure distribution are carried out by applying the pressure distribution law and variation characteristics obtained from the analysis.Pressure sensor arrangement scheme of leakage detection system is given according to normal pressure distribution law,mud leakage criterion based on pressure monitoring is designed by comparing pressure distribution change characteristics of normal and leakage condition.The design of experiment(DOE)is conducted with the optimal Latin hypercube design method(OLHD),and the sensitivity of the variables is analyzed.The main influencing factors are obtained and the range of variation is designed.The polynomial response surface surrogate model is constructed by using the same method of DOE to generate sampling space.While getting at somewhat accuracy of surrogate model,the multi-objective optimization algorithm is used to optimize the pressure drop in both directions of the grease cavity,the optimization solution is verified by simulation.The validation results show that the optimized solution of response surface model make the pressure drop of grease cavity lower and thus enhance the sealing performance of grease cavity,which is of great reference significance to the setting of the grease injection pressure control and leakage monitoring system in shield tail sealing system.