Pressure distribution in EPB pressure chambers: New insights from computational flow simulations
In mechanized tunneling construction with Earth Pressure Balance (EPB) machines, the conditioned excavated soil paste inside the chamber is employed as the support medium. Information on the actual pressure distribution in the chamber is important to evaluate the effective safety of the tunnel face against loss of stability. On job-sites, pressure sensors are often installed on the bulkhead and the cutterhead to obtain information on the spatial-temporal evolution of the support pressure during the advancement and the standstill of the machine. However, the in-situ measurements based on sensors are very limited and the pressure distribution in the chamber as a whole is still unknown. Therefore, this motivates the use of numerical simulation as a means to gain insight into the spatial-temporal evolution of the pressure as well as to investigate the influences of various parameters on the pressure support ability. In this contribution, a finite element model of an EPB pressure chamber is used to analyse the transport process of the soil paste mixture inside the chamber and the conveyor. As a consequence of the flow simulation, a complete picture of the pressure distribution inside the chamber can be well observed. The numerical model of the chamber contains the realistic geometrical components including the cutterhead rotators, the mixing arms and the agitators in the chamber and the ribbon along the conveyor. Essential characteristics of the pressure distribution in agreement with practical observations reported in literature can be predicted by the numerical simulations. Based on that fact, the unbalanced pressure distribution in the chamber is investigated with respect to the operational parameters of different geometrical components including the cutterhead rotators and the agitator. These analyses provide a basis for assessment of pressure support and pressure stability during tunnel boring of EPB machines.