The interaction between deep seated landslides and infrastructure facilities is a topic of relevant interest in the rock mechanics literature. This paper is to discuss the case of deep seated landslides reactivated during excavation of two large size twin tunnels in Italy. In each case, an overview of the geological, hydrogeological and geotechnical conditions is given. The efforts made in order to gain into the understanding of the complexities involved and the necessary quantification of the stability problems during tunnel excavation are presented. Two- and three-dimensional numerical modelling methods, used as means to back-analyze the reactivated landslide and the interaction with the tunnels, are discussed. It is shown how modelling associated with advanced real-time monitoring may contribute to the understanding of the problems under study.

1 Introduction

During excavation of two large size twin tunnels, in complex geological, hydrogeological and geotechnical conditions, along the new highway under construction through the Apennines in Italy, between Bologna and Florence, progressive ground movements were observed on the ground surface. These resulted from the reactivation of deep-seated landslides due to tunnel excavation.

Based on the working classification of landslides to assess the danger of natural slopes (Cruden & Lan 2014), the landslides of interest are "reactivated, complex, very slow moving rockslides, due to artificial causes" such as tunnel excavation. Surprisingly, however, the latter cause is not explicitly indicated in the checklist of landslide causes proposed by the Working Party on World Landslide Inventory (1994) as given in Cruden & Lan (2014).

Due to this, the main motivation for writing this paper stems from the above consideration. The aim is to bring the attention on this important "artificial cause", which need be considered with the most care possible, in view of the consequences that may derive when tunnels are excavated under inhabited areas and in the near vicinity of existing infrastructures. In addition, one is not to neglect the problems deriving for assessing the conditions for opening these tunnels to traffic and maintaining them in service in future years.

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