Publication Abstract

Proceedings-DFI-India 2016: 6th Conference on Deep Foundation Technologies for Infrastructure Development in India, (DFI)

Ground Freezing Combined Method for Urban Tunnel Excavation
Filippo Mira-Cattò, Rodio Geotechik AG, Urdorf, Switzerland, Andrea M. R. Pettinaroli, Studio Andrea Pettinaroli srl, Milan, Italy, Elena Rovetto, Studio ingegneria Balossi Restelli e Associati, Milan, Italy

The construction of Powisle station of Metro Warsaw Line 2, in Poland, required the execution of two shafts next to an urban road tunnel adjacent to the Vistula River. The shafts were linked by three conventionally mined tunnels to be excavated 10 m below the water table level, into an upper sandy and sandy silty layer and a lower stiff clayey stratum. After a failed dig attempt under the protection of jet grouting and forepoling, it was decided to deal with the tunnels excavation problem by using the ground freezing technique as a temporary, non-polluting geotechnical treatment, keeping in service the upper road tunnel. The planning of the activities and the executive phases had a significant importance for the success of the work. For work scheduling reasons the mixed system was adopted, i.e. using both the liquid nitrogen system and the brine freezing method. The freezing process management, with a real time evaluation of the soil temperature measured by thermometric strings and an accurate monitoring of the overlying road tunnel structure, allowed the tunnel excavation and lining stages to be performed under difficult conditions, without water leaking from the frozen ground shell, within the expected times and saving extra costs.

 article #2206; publication #1020 (INDIA-2016)