The role of TBM asymmetric tail-grouting on surface settlement in coarse-grained soils of urban area: Field tests and FEA modelling

This paper examines the role of TBM tail-grouting on surface settlement of coarse-grained soils in urban area. The influence of tail grouting on the ground surface settlement is firstly demonstrated through a challenging shield-driven tunnel project in Beijing City, China. FEA modelling incorporating the excavation sequence and tail grouting details is then set up to support the field observations, based on which the influences of different TBM tail-grouting parameters on ground settlement are investigated, especially the asymmetric tail-grouting in which one of the two grouting openings at the upper part of the shield tail is malfunctioned. It is shown that the grouting volume variation is inconsistent with the development of the grouting pressure, and the ground deformation in coarse-grained soils is directly related to the tail-grouting pressure rather than the grouting volume ratio. Asymmetric tail-grouting will result in notable offset of the maximum surface settlement point in settlement trough from tunnel centerline which correlates exponentially with the parameter ? defined to represent the asymmetry ratio of the grouting pressure.