Abstract: The process of shield tunneling at Chengdu Metro Line 1 in sandy cobble ground is simulated in meso-scale and marco-scale by laboratory experiment and using particle flow code in 2D (PFC2D) and finite element software of Plaxis 3D, respectively. The settlement character and failure mechanism driving by earth pressure balance shield (EPBS) in sandy cobble ground are revealed. Based on the comparison of the estimated values from meso and macro simulation results with the in-situ soil settlements and construction parameters, the surface settlement trough and subsidence patterns are approached. The influence of the chamber pressure at the tunnel face and the grouting pressure at the tail gap on the ground surface subsidence are analyzed; and the suitable values for the chamber pressure at the tunnel face and the grouting pressure at the tail gap are suggested. Compared to the grouting pressure, chamber pressure has relatively smaller effect on both the shape of the curve and the maximum surface settlement based on the analysis results. However, much attention should be paid to the chamber pressure, which may have greatly influence on the stability of the tunnel face and result in abruptly collapse in sandy cobble ground due to the effect of arching.

Key words: sandy cobble, shield tunneling, surface settlement, meso-macro analysis