Soil movement mechanism associated with arching effect in a multi-strutted excavation in soft clay

•The contours of soil movement and shear strain are obtained by full-scale test.•Plastic flow occurs as soil arching develops to the ground surface.•Ground settlement increases dramatically when plastic flow occurs.•The soil in the shear zone is disturbed and verified by cone penetration tests.•A new parameter is proposed to characterize soil arching development. Arching effect behind the wall in a multi-strutted excavation is a soil stress transfer process related to differences in stiffness between the well-braced soil and the underlying soil. This effect has been demonstrated by studies on soil stress transfer and lateral wall pressure in the literature. However, the soil movement mechanism associated with the arching effect is still unknown. In this study, a multi-strutted excavation in soft clay in Ningbo was closely monitored to determine the contours of the total soil movement and engineering shear strain, and these data were then used to produce a detailed interpretation of soil arching development and its influence on soil movement. It is found that plastic flow occurs behind the wall as soil arching develops to the ground surface, resulting in a large soil movement zone and a dramatic increase in ground surface settlement. The soil in the shear zone is also disturbed and verified by cone penetration tests. In addition, this study proposes that the ratio between soil volume loss due to ground surface settlement and soil volume gain due to wall deflection can be used to characterize soil arching development and its influence on soil movement. This study improves the understanding of the soil movement mechanism behind walls in multi-strutted excavations in soft clay, which is very important for protecting adjacent structures and facilities.