Prediction of ground vibrations due to a tunnel boring machine

Abstract

Changing social needs and increases in traffic have led to the demand for increased infrastructure. Due to the limitation of space in urban areas, underground structures, such as tunnels, are becoming more important for potential infrastructure. Tunnelling under city streets has now become a common activity for nearly all types of transportation. The construction of a tunnel induces ground vibration, which may affect the existing surface structures, particularly when the tunnel is constructed in hard ground, such as rock, or is at shallow depth. It is necessary to ensure that historically and economically important structures will not be adversely affected by tunnel construction and that any effects will be within acceptable limits. This programme of research involved carrying out laboratory tests to determine the dynamic properties, such as the small strain shear stiffness and the damping ratio, of Dublin boulder clay. It also involved predicting, using 3-D finite element modelling (FEM), the vibrations at the ground surface due to construction of the north bound Dublin Port Tunnel and the south bound Dublin Port Tunnel. Further, it also involved the development of a new semi-empirical method for estimating the vibration level at the surface above a tunnel boring machine (TBM). Finally, a comparative study was carried out to compare the vibrations predicted using the 3- D FEM and those predicted using the empirical methods with the measured vibrations. Several parametric studies were carried out to examine the sensitivity of the predicted vibrations to variations in the various input parameters including variations in the small strain stiffness and the damping ratio of soil.