Application of an effective stress design method to concrete piles driven in Mexico City clay

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Abstract
Piled foundations are used widely in the lake clay zones of Mexico City, with “friction” piles being driven into soft diatomaceous clay deposits that show an extraordinary range of mechanical properties. The paper assesses the applicability of the Imperial College pile (ICP) design method to the concrete piles driven in these deposits. After the ICP methodology and Mexico City ground conditions are reviewed, an experimental study is reported of the key soil properties required for the ICP procedures: yield stress ratio, unit weight, interface friction angle (δ), sensitivity (St), and intrinsic properties. The new data are then applied to a specially assembled database of static pile load tests from different Mexico City clay locations, with allowance being made for site-specific details and local installation procedures. A quantitative assessment shows that the ICP methodology is free from significant bias and leads to more reliable estimates of static capacity than the total stress (α) design method routinely used in Mexico City.Key words: validation, database, static axial pile capacity, driven friction pile, effective stress design, silty clay.