Abstract

CARREON-FREYRE, Dora C.; HIDALGO-MORENO, Claudia M.  and  HERNANDEZ-MARIN, Martín. Fracturation mechanisms of clay deposits in urban areas. The case of differential deformation in Chalco, State of México. Bol. Soc. Geol. Mex [online]. 2006, vol.58, n.2, pp.237-250. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2006v58n2a6.

Fracturing of clayey lacustrine deposits below urban areas has become a major problem in several cities of central Mexico. The available data reveals the coexistence of several factors determining fracturing at different scales. As main factors we analyze in this study: the variation in compressibility of sediments causing differential deformation and withdrawal of groundwater causing a drop in pore pressure. Compressibility depends on consolidation, a term that in soil mechanics refers to the expulsion of interstitial water, and provokes volume decrease and land subsidence. Although major volume decrease occurs in the vertical scale, consolidation of silty clayey materials generates also horizontal tensile stresses. Considering that this factor can be determining to the generation of fractures, in this study we analyzed the deformational conditions of a silty clayey sequence integrating their stratigraphy and mechanical characteristics. A particular emphasis is made in the mineralogical heterogeneity of the clay fraction that can be related to compressibility variation and generate fracturing by differential deformation. As a study case we analyze the mechanical and geological properties of the Chalco lacustrine sequence in order to relate these properties with the differences in compressibility of materials. The paleoenvironmental history determines the type and degree of crystallization of different clay minerals, grain size, and history of lithostatic loads. Thus, the fracturing in fluvial lacustrine deposits is not a random phenomenon but is highly dependent of the geological properties of materials. We consider that the analysis of the parameters determining the generation of fracturing should permit a more precise evaluation of their propagation and of the implied danger to urban infrastructure.

Keywords : Compressibility; Deformation; Lacustrine deposits; Clays; Fracturing.

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