Abstract: Shield-soil interaction is a complex multiphase coupling problem during the change of shield attitude. According to the critical attitude parameter of the shield pitch angle, based on the ground reaction curve, the shield-soil interaction relationship is simplified by using an equivalent soil spring, and a shield-soil interaction model is established. The initial boundary problem of shield-soil interaction is solved by the improved method of the loosening earth pressure of Terzaghi's theory. A theoretical calculation method of shield pitch angle is further obtained. Moreover, the effects of the vertical coefficient of subgrade reaction and upper-soft lower-hard ground on shield-soil interaction are analyzed and discussed. The results show that the upper-soft lower-hard ground is unfavorable to the control of the shield attitude, and the requirements for shield attitude control become high. Finally, the measured data of the pitch angle of the R2 line shield tunnel project of Jinan Metro are compared and analyzed. The results show that the deflection moment applied by the jacks cannot fully act on the shield, resulting in the measured values are generally slightly smaller than the theoretical value. The theoretical calculation method of shield pitch angle can provide theoretical guidance for shield attitude control.

Key words: shield, pitch angle, shield attitude, interaction