Introduction

The middle of the 19th century, pumping from deep wells induced regional subsidence in the city and additional differential settlements were brought about on the old buildings. Underexcavation of buildings in Mexico City was first used in the early seventies. In 1989, damage that accumulated in the Metropolitan Cathedral prompted local authorities to initiate a project to salvage and preserve it and the adjoining Sagrario Church, which were underexcavated between August 1993 and June 1998. The Cathedral and Sagrario suffered differential settlements during the 20th century in spite of underpinning campaigns that were carried out to prevent their occurrence. Geotechnical work was developed in five major stages: preliminary studies: detailed design and its experimental demonstration; execution of the underexcavation; experimental grouting; and mortar grouting of the soil mass. The success of the field tests justified the execution of an experimental section at the western atrium and the preparation of a project for soil hardening under the Cathedral and the Sagrario.