Efraín Ovando-Shelley

Mexico City’s Metropolitan Cathedral and Sagrario Church 13 Years After Underexcavation and Soil Hardening

ABSTRACT In this article, we briefly discuss the main features and the most relevant achievements of the Project for the Geometrical Correction of Mexico City´s Cathedral and Sagrario church during which these two monuments were underexcavated to correct differential settlements and where the underlying subsoil was later hardened with mortar grouts. Based upon instrumental observations and field test data, we describe the effects on the subsoil of the selective soil hardening that took place when underexcavation finished. We also look at the behaviour of both churches after more than 13 years after the end of underexcavation and soil hardening. Topographical data show that soil hardening has positively modified the response of both temples and that further interventions are not likely to be needed in the short and mid term.

Mexico City: Geotechnical Concerns in the Preservation of Monuments

This article presents and describes four case histories, which demonstrate that the role of geotechnical engineering in the preservation of architectural monuments in Mexico City is of paramount importance. Extremely soft soils and regional subsidence have combined to induce damaging differential settlements in a large number of monuments built in the former lake area. Hence, preservation of monuments in the city includes devising geotechnical solutions for correcting, reducing, or arresting differential settlements. The article points out the advantages and limitations of traditional solutions such as surface footings or the use of deep point bearing piles with devices for regulating the magnitude of loads applied on their heads. Other less well known solutions (underexcavation, mortar injection, and the use of isolation trenches) are also described and assessed critically.

Numerical Study of the Seismic Behavior of Rigid Inclusions in Soft Mexico City Clay

This article shows how seismic ground response is affected by the presence of a group of rigid inclusions embedded in deposits of soft Mexico City clay. The 3-D finite difference code FLAC3D was used to perform numerical analyses in which different configurations of inclusions were studied, including in some of them surface buildings, to incorporate important inertial effects. Results showed that inclusions, together with the surface structure, modify seismic ground response on account of soil-structure interaction.

Neural estimation of strong ground motion duration

This paper presents and discusses the use of neural networks to determine strong ground motion duration. Accelerometric data recorded in the Mexican cities of Puebla and Oaxaca are used to develop a neural model that predicts this duration in terms of the magnitude, epicenter distance, focal depth, soil characterization and azimuth. According to the above the neural model considers the effect of the seismogenic zone and the contribution of soil type to the duration of strong ground motion. The final scheme permits a direct estimation of the duration since it requires easy-to-obtain variables and does not have restrictive hypothesis. The results presented in this paper indicate that the soft computing alternative, via the neural model, is a reliable recording-based approach to explore and to quantify the effect of seismic and site conditions on duration estimation. An essential and significant aspect of this new model is that, while being extremely simple, it also provides estimates of strong ground motions duration with remarkable accuracy. Additional but important side benefits arising from the model’s simplicity are the natural separation of source, path, and site effects and the accompanying computational efficiency.