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Mexico City has a decades-old problem with severe consequences: its lacustrine zone is subsiding due to pumping of potable water from the main aquifer. The geotechnical team assigned to work on the problem assessed the situation by using remote-sensing methods. This article describes the present situation as well as a new approach to mitigate the effects of subsidence. The new approach combines several actions, but consists mainly in progressively modifying the pumping strategy to avoid exceeding the soil preconsolidation pressure in the clayey compressible layers, including the superficial aquitards and in most of the main aquifer.

espanolLos acuiferos estan siendo severamente sobre-explotados en muchas partes del mundo conforme al continuo aumento de las poblaciones urbanas. Ademas, la excesiva extraccion del agua subterranea de los acuiferos ha acelerado dramaticamente la consolidacion de los acuitardos sobre-yacientes, creando severos hundimientos del terreno y muchos otros problemas relacionados. La Ciudad de Mexico, con una poblacion de 20 millones de habitantes y un acuifero principal exhausto, es un sitio que ofrece excelentes condiciones para experimentar tecnicas de compensacion. En este articulo, se propone una estrategia con el proposito especifico de mitigar el hundimiento del subsuelo de la Ciudad de Mexico. La estrategia consiste en aumentar la presion de poro en el acuifero somero por debajo de la Ciudad de Mexico con la intencion de inducir un proceso de difusion a traves de los acuitados superior e inferior, para generar incrementos de presion de poro en el sistema que contrarresten los actuales descensos de presion de poro asociados a las extracciones de agua subterranea en la unidad acuifera principal. La estrategia se analiza analiticamente y se utilizan parametros hidraulicos tipicos del sistema acuifero-acuitado somero por debajo de la Ciudad de Mexico sujeto a un pozo de inyeccion. Los resultados proporcionan, por primera vez, las respuestas hidraulicas acopladas del sistema sujeto a la inyeccion de agua y proporcionaran datos utiles cuando se realicen pruebas de inyeccion en el futuro cercano. EnglishAquifers are being severely overexploited in several sites around the world as urban populations continue to grow. Excessive groundwater subtraction of aquifers has also accelerated the consolidation of the overlying aquitards dramatically, creating severe land subsidence and many other related issues. Mexico City, with its population of 20 million inhabitants and depleted main aquifer, is a prime site for experimental approaches for redress. In this paper, a purpose-specific strategy for the land subsidence mitigation of Mexico City is suggested. The strategy consists of rising depleted pore pressure in the shallow aquifer beneath Mexico City to induce a diffusion process through the upper and lower aquitards that generate increments of pore pressure in the system to counteract current pore pressure declines associated to groundwater withdrawals of the main aquifer unit. The strategy is analyzed on the basis of analytical solutions and typical hydraulic parameters for the shallow aquifer-aquitard system beneath Mexico City subject to one injection well. The results provide for the first time the coupled hydraulic responses of the shallow aquifer-aquitard system beneath Mexico City subject to water injection and provides useful data for field injection tests to be conducted in the near future. Key words

A new geotechnical zoning map for the subsoil of Mexico Valley is presented. This proposal is based on a Geographic Information System for Geotechnical Borings (GIS-GB), which contains over 10000 soil profiles. In addition to the geotechnical information, available topographic and geological data on the studied area were taken into account. Geostatistical techniques were used to assess the spatial distribution of the thickness of the lacustrine clay deposits within the area down to the so-called deep deposits. As a result, a contour map was obtained that was used to update the current geotechnical zoning map for Mexico Valley. It has been proposed to include this new map into the Building Code for the Federal District (Mexico City).

The paper shows how axisymmetric finite element numerical models can be used to optimize the design of friction piles foundations in an environment that is prone to regional subsidence. The study considers friction piles in typical Mexico City soft clays, that are subjected to external loads and soil consolidation due to variations in piezometric conditions. The constitutive models used to numerically simulate the behavior of the clays vary from a basic elastic perfectly-plastic model to a critical state model that is able to account for the anisotropic yielding behavior of Mexico City clay. The simulations consider the long term behavior of the internal piles within a large pile group.