ABSTRACT
Vertical shafts are an essential component of tunnelling projects in urban environments and elliptical plan geometries are sometimes constructed. However, little is known about the performance of elliptical shafts and the associated adjacent ground movement during excavation; centrifuge testing of elliptical shaft excavation can provide valuable insight. Traditionally, excavation simulations in centrifuge testing mainly rely on the use of heavy fluid which is drained in-flight. This method assumes that the horizontal stress changes within the excavation are equal to the vertical stress changes which may not be the case in reality. More realistic stress changes could be achieved by carefully extracting sand from the centre of an elliptical shaft during excavation. This paper describes such centrifuge tests conducted at Cambridge University. The centrifuge model and the mechanism developed to excavate the shaft in-flight are described. Measurements are presented for strains in the elliptical shaft lining and associated ground displacements.
