Optimal control of an earth pressure balance shield with tunnel face stability

•The shield's tunnel face is optimally controlled by the speed of the screw conveyor.•A certain stable working range is determined for shield's stable tunneling.•A normal vector angle on the chamber pressure field is used to set the stable range.•The chamber pressure field is modeled by the shield's excavating data online.•The particle swarm optimization algorithm is used to find the optimal screw conveyor speed.

To ensure security during the excavation process of an earth pressure balance shield, this paper presents an optimal control method that accounts for the tunnel face's stability. The tunnel face is controlled by an optimal screw conveyor speed derived from the particle swarm optimization algorithm for a designed stable normal vector angle range on the distribution surface of the chamber pressure field. These normal vector angles can be computed online by measuring the changes to the earth pressure in the shield's chamber using a BP neural network model of the chamber pressure field distribution. An experimental example that uses excavation data from an actual EPB shield is given to illustrate the effectiveness of the proposed method.