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.
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 drainage system of Mexico City, one of the largest metropolitan areas in the world, is formed by a large network of interceptors and collectors leading to the main outlet: a 49.3-km-long tunnel with a 6.5 m diameter. To build the access shafts to the tunnels of the system and the deep sumps of the pumping stations in the very soft clays of the lacustrine area of Mexico valley, a technique known as ''flotation method'' has been commonly used since 1969. The paper presents the main construction steps followed and some aspects of the analysis and design of shafts constructed by this technique. The experience gained obtained after more than 30 shafts have been constructed by this method, and the actual trends in its application are also discussed.
The design of a trench of granular material is shown. This design can be used to mitigate the damages caused by cracks that have appeared in the soil in certain zones of Mexico City. The most destructive cracks are associated with differential settlements due to the regional subsidence of Mexico City and can show escarpments of considerable height. The proposal solution consists of constructing a trench of sand on the crack line, called “Dissipative box of unit deformations”. The trench behavior is assessed by means of numerical simulations with discontinuous media approach using the discrete element method. It is drawn that the unit deformations (differential settlements/horizontal distances) on the surface decrease when the depth of trench increases. The simulations allow to obtain an optimal design of the dissipative box distributing the vertical displacements in a sufficient horizontal length so that the escarpment disappears and is replaced by a surface with moderate inclination. In this way, a road affected by a crack can continue open to traffic. Analyzes with continuous media approach are presented, their results are compared with the discrete approach ones. Some conclusions and practical recommendations for the mitigation of damage caused by cracks are given.
In this paper, an analysis of the behavior of an individual friction pile subjected to negative skin friction and transient loads (seism or wind) for typical stratigraphic and piezometric conditions of Mexico City lacustrine zone is presented. This analysis is performed using a two dimensional finite element model (2D FEM) and taking as a reference the field and laboratory researchs on individual point bearing piles developed by Fellenius (1998), Bozozuk (1981) and Leung et al. (2004). A 2D FEM study of an internal pile within a pile group subjected to the weight of the structure and to negative skin friction is also presented. Finally, for the same conditions, 3D FEM analyses results are presented in order to assess the behavior of border and corner piles. Some criteria are proposed regarding design loads and negative skin friction estimation for internal, border and corner piles.
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