Vedeggio-Cassarate Road Tunnel - Section in Loose Material
The Vedeggio-Cassarate tunnel (L = about 2'630 m) connects the Vedeggio valley in the west with the Cassarate valley in the east, near the city of Lugano, Switzerland. The tunnel is flanked by a safety tunnel at a distance (interaxis) of 30 m along its entire length.
In the first 200 m from the Cassarate portal, the tunnel crosses extremely heterogenous quaternary deposits consisting of fine sands with silt, sandy and clayey silts, from medium to strongly consolidated and generally not very permeable. The paleochannels of the Cassarate river are interspersed in these soils, filled with coarser fluvial deposits with higher permeability which appear as layers or lenses in which pressurized aquifers (artesian groundwaters) with water levels reaching up to 20.0 m above ground level can be found. On the surface there are some residential buildings and the high school of Canobbio.
For the excavation, the ground was pre-consolidated both from the surface in the initial section (10 m for the safety tunnel, 30 m for the main tunnel) with a low covering, and starting from the heading face on the next section up to the contact with the rock.
The consolidation from the surface was achieved by using by-fluid jet-grouting forming vertical secant columns. The underground consolidation for both tunnels was performed in dvance of the excavation front with single-fluid jet grouting at the boundary of the excavation and in the excavation face. The jet-grouting columns are 15.0 m long and have an overlap of 5.0 m.
Due to the presence of several residential buildings and the Cantonal High School on the surface, an intensive measuring system (total station, extensometer, piezometer, etc.) with automatic data supply is set up. Part of this is the measurement- and intervention concept, which defines the structure and responsibilities of the monitoring team as well as intervention measures for the different alert levels.
Canton Ticino, Dipartimento del Territorio, Divisione delle Costruzioni
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Civil designs; Construction supervision