Hydrogeological Prognosis with Regard to Realisation of the New Colle Di Tenda Road Tunnel

Problem statement: The doubling of Tenda pass road tunnel jointing SW France to Piedmont (Italy) was planned to penetrate a complicate rock structure in which several complex play an hydrogeologic role including carbonate-Karst aquifer between flysch impervious complexes. The main problem of the project is the presence of an hydraulic circulation feeding a spring of social and economic great importance discharging into a railroad tunnel below. Approach: The authors was charged by ANAS, Italian National Roads Authority, to execute a complete hydrogeologic prognosis of the situation that will be determinate by the excavation of the new tunnel and forecast as well as possible the hazard for the tapped spring. Results: Two years research have included a complete hydrogeologic and hydrochemical survey all the hypothesized structure feeding the spring, with several bore holes used as observation wells, the use of several monitoring device for the discharge and the chemical characters of spring, a lot of laboratory tests on cements and micro-cements and other materials used in waterproofing and sustain the rocks during the excavation and the concrete lining of the tunnel. Conclusion: The study ends with the evaluation of the vulnerability of the spring and the forecasting of contamination and depletion of the spring.