TBM And NATM Combined Solution For A Very Deep Tunnel?The ?Pajares? Case

INTRODUCTION The high speed rail link between Madrid and Asturias, in the North of Spain, has encountered in the Cantabrian range the biggest challenge of the whole line, a very deep tunnel, 25 km long through a foreseen difficult geology. This tunnel was divided in the following four lots for construction: ¦Lot 1: Pola de Gordón- Folledo. L=10,7 km ¦Lot 2: Folledo-Viadangos. L=4,166 m ¦Lot 3: Viadangos- Los Pontones. East tube. L=10,4 km ¦Lot 4: Viadangos- Los Pontones. West tube. L=10,4 km. Dragados S.A. leading a JV was contracted to design and built the Lot 2 on the captioned Pajares High Speed Railway Tunnel. The Lot 2, comprising the middle third section of the 25 km long tunnel has an additional challenge: the construction of one access from the surface to allow it own construction. Feasibility reports and preliminary design do not foresee the use of TBM due to the risk of squeezing ground at the deepest area of the tunnel. On the other hand, conventional NATM excavation of the twin tunnels and ancillary works, including access shafts were against the expected construction schedule by the client, due to the poor ground foresee at the early stage.