Centrifuge modelling of shaft excavations in clay

Circular shafts are an integral component of tunnelling projects and can be located very close to buildings and services in urban environments. They enable access of equipment, personnel and material to the tunnel horizon and also provide ventilation and/or emergency access to the completed tunnel. The current state of knowledge concerning the behaviour of circular shafts and the ground movement associated with their construction is limited. Consequently, any conservative assumptions made in the design of the shaft lining or to estimate ground movement due to their construction can have considerable cost implications for tunnelling projects. This paper describes a small-scale model test performed in a geotechnical centrifuge to simulate shaft excavation in clay. The centrifuge model and procedure developed to excavate the shaft in-flight are described. Measurements are presented for instruments used to monitor the response of the shaft lining as well as the adjacent ground