25 YEARS OF SUBWAY CONSTRUCTION IN MEXICO-CITY

Construction of Mexico City's subway system began. in 1968. At that ti me, the nature of the Mexico City subsoil, as well as aggressive regio nal settlements and seismicity conditions, posed serious challenges to the project. Despite the obstacles, to date more than 150 km of subwa y line have been constructed. The first lines were constructed using t he underground, open caisson method; Eater lines were built overhead, in tunnel (successfully using the NATM) and on the surface. In some ca ses, excavations down to more than 15 m depth were executed close to b uildings of significant historical and architectural value. To accompl ish this, accurate construction procedures were used to cross the exis ting lines without discontinuing their operation at any time. This pap er summarizes these experiences and offers some reflections on the fut ure of underground excavations in Mexico's capital city for uses such as parking lots and commercial passageways.