Alguns problemas da construçao e modelaçao numérica de tùneis pouco profundos

The construction of shallow tunnels has today a large development, mainly in urban an sub-urban areas. This kind of tunnels put important stability problems, particularly those excavated in soils or soft rock. These problems are presented here together with techniques for their solution. Also the case of numerical modelling of a railroad tunnel excavated in an aluvial soil is presented. Techniques of back analysis are applied using finite elements conceming escavationlconstruction processes for two distinct cases. Two finite element solutions are considered: one elastic with reduced Young moduli at zones of large shear; and another elasto-plastic