ABSTRACT:

A computer simulation of the tunnelling procedure carried out for the new underground railway lines in Madrid is presented in this paper. First the excavation procedure and the details of the construction of the tunnel structure is explained. Then the set of finite elements model including several materials is described. The settlements induced by the excavation were obtained using nonlinear structural analysis and the numerical results produced by varying several parameters are contained in the paper along with the conclusions.

THE MADRID UNDERGROUND RAILWAY TUNNEL

A vast extension of the network of underground railway has taken place in the city of Madrid during years 1996–1999. The whole process of tunnelling works was made using the same procedure, which is next summarized. The front section of the machine is moved forward by a set of cylinders and the equilibrium at the excavation front is obtained by an earth pressure balance system (EPB). A steel shield arranged around the machine allows placement of final tunnel structure. Segment lining elements of precast concrete compose the final tunnel structure. They are placed at the tailpiece of the machine and cement grouting is used to fill up the void between the concrete elements and the ground. Once the lining is finished the machine is advanced by thrusting on the tunnel structure.

FINITE ELEMENT MODELLING

Evaluation of settlements produced by tunnelling was based for many years on empirical or analytical formulae (e.g. Peck, 1969) and it took a few years for the finite elements method to be used in soil mechanics problems (e.g. Ghaboussi, 1978; Tan and Clough 1980). In this paper the excavation procedure was simulated by using a finite element model of the tunnelling devices, tunnel structure and surrounding ground.—Ground material: In some models the ground material was considered homogeneous.

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