Back analysis of the measurements performed during the excavation of a shallow tunnel in sand

The results of back analyses based on the displacements measured during the construction of a railroad tunnel in an alluvial sand deposit are presented. After illustrating the characteristics of the construction technique, the main aspects of the in situ measurement programme and of the finite element approach used for back analysis are summarized. Then, the results of a series of calculations are discussed that concern both the determination of the elastic moduli of the soil deposit and the attempt to identify the mechanism governing the development of the surface settlements. On the basis of these results some comments are presented on possible improvements of the adopted excavation/construction procedure.