Stress Responses Associated with Earth Pressure Balance Shield Tunneling in Dry Granular Ground Using the Discrete-Element Method

This study investigates stress responses associated with earth pressure balance (EPB) shield tunneling in dry granular ground. A numerical model using the discrete-element method (DEM) was employed to simulate both the advancement of EPB shield and the discharge of muck from the chamber. Some critical ground stress variations associated with tunneling were thus effectively captured. Numerical results show that the responses of the principal stress in dry granular ground, namely changes of magnitude and rotation angle, significantly depend on both the discharge rate of muck and the distance from tunnel face. The average value and distribution features of stress at the tunnel face are also subjected to the discharge rates of muck in the shield chamber. To be specific, in the case without muck discharge out of the chamber, the average stress at the tunnel face first increases with increases in advancement distance and subsequently tends toward a stable value. But for the case of discharging muck with an upper limit rate, the stress first decreases rapidly to a minimum value and subsequently increases to a stable value. Further, a significant stress release area is also found in the proximity of the tunnel face, and the changes in the contact forces among soil particles are far less than those in the case without muck discharge.