Use of Electrical Resistivity Tomography (ERT) as a tool to characterize a clayey subsoil in urban areas at risk: Case study in Mexico City

The results obtained with the Electrical Resistivity Tomography in 3D (ERT-3D) are presented for the characterization of the subsoil in a residential area located towards the NE of Mexico City, due to the appearance of a fracture in this area. Such an effect caused a series of damages to homes and civil infrastructure, which was attributed to a leak from a sweet-water pipe. Subsequently, several houses had to be evacuated and their residents moved. These houses are seated on clayey materials, of what constituted the ancient lake of Texcoco.

This work had the purpose of identifying features that could be a risk for the inhabitants, as well as to being able to carry out a comparison between surveys done in two different seasons of the year: the rainy and the dry seasons.

Three different types of non-conventional arrays were employed, given the impossibility of performing a traditional 3D study; the Wenner-Sclumberger Perimeter (WSP), Minimum Coupling (MC) and Gradient (G), where the electrodes surrounded this habitational complex. Such arrays allowed for an adequate coverage of apparent resistivity observations in the subsoil.

The survey was repeated for the rainy and dry seasons. The results show a complex subsoil, observing subsidence zones and a possible cavity at a depth of 12 m. The study carried out in the rainy season shows a very saturated clayey subsoil (Fig.1). In the survey carried out during the dry season, a series of high resistivity anomalies associated with a piping process were more clearly detected. This effect continues to increase in the investigated area.

We inferred areas where there is a high concentration of water that causes differential subsidence, whose depths vary between the surface level and in some cases up to 15 m deep. This is reflected in the extensive damage to homes and urban infrastructure observed today.