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Soil Fracturing Induced by Land Subsidence in Mexico City
Fracturation des sols induite par la subsidence de la ville de Mexico
Auvinet G., Méndez E., Juárez M.
Instituto de Ingeniería, UNAM, Mexico
ABSTRACT: Updated information concerning land subsidence and associated soil fracturing in Mexico City is presented. Subsidence
was estimated from the evolution of the elevations of 2064 benchmarks and other references located in former Texcoco Lake.
Geodesic and topographic surveys carried out in the middle of the XIXth century proved to constitute an excellent initial reference for
subsequent measurements of land subsidence. Extensive use was made of new geocomputing tools to process these data. Results of
surveys of soil fracturing associated to subsidence are also presented and discussed.
RÉSUMÉ: On présente des données récentes sur la subsidence et la fracturation des sols à Mexico. La subsidence a pu être évaluée
grâce à des levés topographiques portant sur 2064 points de nivellement et d’autres repères situés dans l’ancien lac de Texcoco. Les
relevés géodésiques et topographiques du milieu du XIXème siècle constituent une excellente référence initiale pour les mesures
suivantes. On a utilisé de nouveaux outils informatiques pour traiter ces données. Des résultats de relevés concernant la fracturation
des sols sont également présentés et commentés.
KEYWORDS: Subsidence, soil fracturing, soft clays, surveys, geocomputing.
1 INTRODUCTION.
The demographic development in Mexico City has created an
accelerated demand of services, mostly of potable water. One of
the cheapest ways to meet this demand has been the exploitation
of the local aquifer by pumping water from deep wells. This has
produced a water pressure drawdown in the subsoil that in turn
is causing general subsidence of the former lacustrine area and
soil fracturing. This problem has been around for almost a
century but is now reaching new worrying dimensions.
Today, the subsidence phenomenon, at eighty years from
Roberto Gayol’s discovery (1925), and at more than sixty years
from its scientific explanation by Nabor Carrillo (1947), persists
with cumulative effects through time which cause differential
settlements in colonial and modern structures of Mexico City.
Installations as important as the subway system, the Gran Canal,
and the water system network are also severely affected.
During the last decades, an increasing number of soil
fractures have been detected in Mexico City valley. Such cracks
are a matter of growing concern for the population and
authorities since they have caused a series of accidents and
serious damage to constructions and public services. It is now
acknowledged that the soil fracturing problem is an important
risk factor and that the best scientific tools and techniques
should be mobilized to define prevention and mitigating
measures.
Soil fracturing can occur as a consequence of any condition
leading to large tensile stresses or extension strains in the soil.
Accordingly, cracks in the soil have different origin, including
contraction of compressible clays by drying, stresses induced by
the weight of constructions, hydraulic fracturing of soft soils
(Auvinet & Arias, 1991, Figure 1), seismic movements, etc.
However, the largest and more destructive fractures are
generally a direct consequence of land subsidence associated to
pumping of water in the local aquifer.
Figure 1. Crack in Chalco
1 LAND SUBSIDENCE
1.1 Assessing regional subsidence
Although regional land subsidence is an old phenomenon, it has
not been possible to control it. In fact, it is expected to continue
in the future for many more years since, due to the high cost of
other alternatives, water pumping from the local aquifer cannot
be suspended. Studies and analyses are thus necessary to rethink
criteria and strategies to mitigate future effects.
1.2 Local values of subsidence
Thanks to the historic information which was gathered with
the support of different institutions among which stands out the
Water System of Mexico City (SACM) of the Federal District
Government (Pineda & Pelaez, 2009), the subsidence history in
three sites of the Historic Center of Mexico City could be
reconstituted (Figure 2).
