Análisis probabilístico de la falla de fondo en excavaciones urbanas en los suelos blandos de Bogotá D.C., y sus implicaciones en la amenaza por desplazamientos en elementos de la infraestructura vial urbana

Abstract

The document presents a probabilistic approach to the study of the phenomenon of background failure in urban excavations and its implications in the relative threat, associated with surface displacements in elements of urban road infrastructure in the savanna of Bogotá, with emphasis on the analysis of the response of lacustrine clays from the city of Bogotá. The above, motivated by recent cases of substantive failure in Bogotá during the last decade, which have compromised the stability of urban road infrastructure elements for prolonged periods of time (for example, case of Calle 98 with Carrera 11 and Avenida Boyacá with Calle 145), among others that have been presented in the city during the last three decades.

A parametric study was carried out based on the analysis of the information collected, which will be obtained from reliable sources such as district entities (Urban Development Institute - IDU, Aqueduct and Sewerage Company of Bogotá - EAAB, District Institute of risk management and climate change - IDIGER, among others). Then, the information was collected in a database from approximately 70 projects carried out in the savanna of Bogotá, with which an average profile was subsequently determined and from this, a stability analysis was performed for typical excavations in the city, a probabilistic analysis in order to establish the probability of failure and the prediction of vertical displacements through modeling by means of finite elements. Finally, with all the established parameters and the geometry of the excavations, a matrix of probability of occurrence of failure expressed in the threat determination is proposed.

From the database and applying statistical measures such as standard deviation and percentiles, an average profile was determined which resulted in soft clays in the upper strata and clays with the presence of sands in the lower strata, with an average water table at 3.50 m deep. With the established materials and parameters, the models and subsequent analyzes were carried out.

As for the modeling, the previously obtained information (database) was introduced to the Slide software of the Rocscience house, which works under the limit equilibrium methodology and using the “probabilistic analysis” module, a resistance analysis was performed. The simulation of scenarios for the prediction of vertical displacements of the physical environment was continued with the help of Phase2 software, also from the Rocscience house, which works under the finite element methodology. Then a relationship between geometry and vertical displacement, called angular distortion, was defined, which allowed the base and height of the excavations to be correlated within the suggested threat matrix. As for the threat matrix, as a result and main contribution of this document, three levels are proposed: low, moderate and high, in which throughout the process it was found that for excavations less than 3.0 m deep the threat it is between low and medium and, for excavations between 6.0 m and 12.0m, the threat is high, increasing as loads increase.