THE PREDICTION OF SURFACE SETTLEMENT PROFILES DUE TO TUNNELLING

Recent work has shown the importance of modelling the small strain stiffness of soil when predicting ground movements adjacent to excavations. This paper describes a simple constitutive relation for the undrained behaviour of overconsolidated clays. A power law expression determines the non-linear elastic stiffness of the soil at small strains. When the undrained shear strength is mobilised the soil yields according to the Tresca criterion. This model has been implemented in the geotechnical finite element program CRISP. The paper describes the application of this model to the prediction of ground surface movements caused by tunnelling. Comparison with analyses which do not model small strain stiffness demonstrate a dramatic improvement in the predictions. Comparisons with empirical relations based on field data indicate that although the 'ground loss' prediction is realistic, the overall settlement profile predicted is still too wide, the maximum settlement being about half that observed in practice. (A) For the covering abstract see IRRD 859983.