The Pajares Lot 4 tunnel

Project Overview

The Pajares Lot 4 tunnel is part of Spain’s AVE high-speed rail link. The entire 49.5 km (30.8 mi) long tunnel connects Asturias to the Madrid-Valladolid high-speed link. The route was divided into four lots, with two tunnels for traveling both east and west.

Project owner, Administrador de Infraestructuras Ferroviarias (ADIF), awarded the construction contract for Lot 4, a 10.5 km long section of tunnel, to a joint venture of Constructora Hispanica, Azvi, Brues y Fernandez and Copcisa. The joint venture chose a 10 m (32.8 ft) diameter Single Shield TBM to bore the tunnel. The TBM was designed by Robbins and built by Mitsubishi Heavy Industries. The machine was pre-assembled at a shop in Spain and final assembly was completed onsite.

Geology

The machine began boring in August 2006 through sandstone, shale, limestone, molasse, and volcanic rocks with Unconfined Compressive Strengths (UCS) of 40 to 90 Mpa (6-13 ksi). Robbins’ Single Shield design allowed the machine to cope with this fractured and varied rock. The machine could also erect 500 mm (19.7 in) thick pre-cast concrete segments to support the tunnel walls in troublesome geology.

TBM and Tunnel Excavation

The TBM featured 17 inch (432 mm) cutters and was powered by 5,180 kW (6,946 hp) to generate a maximum cutterhead thrust of 16,814 kN (3,780,000 lb). The back-up system for the machine consisted of open gantries.  Tunnel excavation was completed in July 2009.