Reducing settlement caused by shield tunnelling in alluvial soils

Shield tunneling methods have become the main methods for tunnel construction in urban areas. However, under extremely unfavorable geological conditions, adjacent structural damage may occur by face instabilities and tail void. It is, therefore, necessary to develop the technology to repress as much as possible the ground deformation caused by shield advancing. This paper describes two sites of the Lyons Metro D line extension (1993-1995). They were intensively monitored and were bored with slurry shield. Based upon numerical modeling and site measurements of the behavior phases of the ground related to the shield advancement, this paper also presents the specified requirements for an inert and very economical back-fill together with a summary of the grouting operations. They have been proved to be very successful in reducing ground settlement caused by shield tunneling in alluvial soils.