Ground Subsidence due to a Shallow Tunnel in Dense Sandy Gravel

Finite-element procedures have been applied to predict ground subsidence caused by tunneling; however, the calculated results are strongly dependent on the adequacy of the model used. The construction of a shallow tunnel in the typical gravel of Santiago (Chile) is herein back-analyzed using a finite-element method based on a modified version of the hyperbolic model. Observed ground subsidence as a function of distance to the face and to the tunnel axis is examined and related to the construction procedure. Although the ratio of overburden cover to excavation width was 0.52, the maximum settlement measured was only 9 mm. It was found that, as a result of the excavation process, a certain thickness of soil behind the excavation line experienced a significant alteration. The hyperbolic parameters of the disturbed soils were determined by fitting the calculated subsidence to the observed results. From the good agreement obtained, it is concluded that the model used represents reasonably well the construction stages of the tunnel and the stress–strain behavior of the materials involved.