ABSTRACT
Regional subsidence seriously affects urban infrastructure in Mexico City. Subsidence and subsidence rates vary depending on geographical location, site-specific geotechnical conditions, structural types and characteristics, and the mutual interactions between buildings or infrastructure elements. When the effects of the regional subsidence became more evident, municipal engineers in Mexico City realized that in order to assess the magnitude of the phenomenon, it was necessary to have reliable topographical references. As part of the underexcavation project for the Cathedral and the Sagrario church, deep benchmarks were installed to determine how settlements within the subsoil are distributed at the Cathedral and at the Sagrario, and also to measure the total regional subsidence. They are constructed with concentric twin pipes; the internal one acts as a reference mark, and it is continuous and rests at the selected depth. The external pipe is deformable, and hence, it absorbs axially the vertical deformations suffered by the soil between the surface and the depth of the benchmark.
