Abstract
For earth pressure balance (EPB) shield tunneling, the stability of tunnel face is controlled by the excavation and discharge rates of soil within tunnel pressure chamber. To ensure continuous discharge of soil from pressure chamber, the soil is required to have favorable plastic flow. However, the plastic flow of conditioned soil primarily relies on experience that lacks relevant theoretical guidance. Additionally, when EPB shields are used for tunneling in deeply buried sandy strata, common soil conditioners may struggle to make the conditioned soil have ideal plastic flow. By assuming the conditioned soil as an ideal Bingham fluid, a simplified soil slump model and a calculated model for passive soil discharge are developed in this study to assess the plastic flow of conditioned soil using yield stress and dynamic viscosity coefficient. By incorporating macromolecular polyacrylamide (PAM) along with fine particles, the conditioned soil could have favorable plastic flow at any slump. Based on the measured soil discharge rate from Hengli - Panyu Square Station of Guangzhou Metro Line 18, the ideal plastic flow and slump of conditioned soil under various tunnel burial depths are derived. The results indicate that as the tunnel burial depth increases, the yield stress of the conditioned soil must be systematically increased, and consequently, the slump must be reduced to ensure the integrity of the earth plug and anti-spewing safety. This study provides a systematic inversion methodology for determining optimal soil conditioning parameters based on burial depth, offering a theoretical framework and safety thresholds for the adaptive management of soil conditioning in deep-buried EPB shield tunneling.