Coatzacoalcos is a port city in the southern part of the Mexican state of Veracruz, on the western bank of the Coatzacoalcos River. The city has a population of about 250.000, making it the third-largest city in the state of Veracruz. The largest community in the municipality, aside from Coatzacoalcos, is the town of Allende, with a population of about 25.000. The town of Allende is situated on the east bank of Coatzacoalcos River.
The city's industry is dominated by the petrochemical sector. The main petrochemical complexes are however located on the east bank of Coatzacoalcos River and can only be reached via an old and heavily congested bridge south of Coatzacoalcos. Work is now under way on a tunnel to directly connect the towns of Coatzacoalcos and Allende. The main challenging design aspects are the rather poor soil conditions and the seismic hazard which are the subject of this paper.