ATG - Gotthard Base Tunnel - Settlement calculations cut-and-cover section Bodio
The Bodio Portal at the southern end of the 57 km long Gotthard Base Railway Tunnel consists of a cut and cover section with two tubes of approx. 380 m length. Both cut and cover tunnels connect the actual portal with the underground section, advancing through a section with heterogeneous blocky soil. Based on the local geology and geological history, no time depending settlements were expected at the beginning of construction.
However, after initial settlements a continuation at a constant low rate, showing almost no changes for years, was observed. As consequence, further ground investigations with deep core drillings up to a depth of approx. 200 m were carried out. Lombardi Ltd. was charged with the interpretation of the results of these additional ground investigations as well as the analysis of possible mechanism including the prediction of the future development of these settlements.
Two mechanisms or the combination of both of them could be identified as possible cause for the still ongoing ground deformation. One possibility is that the settlements are caused by an ongoing consolidation of the deep lacustrine deposits (between 100 m and 160 m beneath the tunnel.
The ongoing deformation could, however, also be referred to creep phenomena within the cohesive formations.
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