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Título del libro: 20th International Congress On Modelling And Simulation (modsim2013)
Título del capítulo: Modeling the deformation of faulted volcano-sedimentary sequences associated to groundwater withdrawal in the Querétaro Valley, Mexico

Autores UNAM:
DORA CELIA CARREON FREYRE;
Autores externos:

Idioma:
Inglés
Año de publicación:
2020
Palabras clave:

Aquifers; Deformation; Deposits; Faulting; Fracture; Geomechanics; Groundwater flow; Mechanical properties; Models; Operations research; Porous materials; Sedimentology; Sediments; Soils; Stratigraphy; Subsidence; Volcanoes; Geological heterogeneities; Geomechanical simulations; Groundwater withdrawal; Land subsidence; Me-xico; Three dimensional finite elements; Three-dimensional stress field; Volcano-sedimentary sequences; Groundwater resources


Resumen:

The City of Querétaro is located on a graben structure that formed a continental basin filled since the Oligocene time with volcanic and sedimentary materials. In the N-W direction two major normal faults are dipping to the West and the thicknesses of the filling materials vary many tens of meters in close distances. The filling materials include lacustrine and alluvial sediments, pyroclastic deposits, and interbedded fractured basalts. Hence, important differences of hydraulic and mechanical properties characterize the various units. Groundwater was been strongly withdrawn over the last three decades in the study area, with a level decline exceeding than 100 m in some areas. Because of the high variability of the geological deposits, a space variable decrease of the piezometric levels, and consequently of the effective stress increase, has been observed. Piezometric variations are also due to faults that strongly impact on groundwater flow dynamics. The variable distribution of the effective stress increase has caused large differential subsidence causing ground fracturing that has damaged the urban infrastructures of the City of Querétaro. The geological heterogeneities of the subsoil were integrated into a flow and geomechanical model to predict the deformation caused by fluid withdrawal. Initially the hydrodynamics of the pumped aquifer system was simulated by a 3-D groundwater flow model and then the subsidence was computed with the aid of a 3-D poro-mechanical model with the pore pressure field specified as an external distributed source of strength within the porous medium. The model is calibrated using observed groundwater and land settlement records, with the generated three-dimensional stress field that is compared with the distribution of the major fractures detected in the city. The aim of this work is to predict the differential deformation of the faulted volcano-sedimentary sequences. The simulation is carried out by an advanced three-dimensional finite-element flowdynamic-geomechanical code. The conceptual model was accurately defined using the correlation of geological logs of extraction wells, field mapping of faults, fractures, and the integration of major structures reported in previous geophysical works. The stratigraphic sequences were simplified with seven mayor hydrogeological units with specific mechanical properties, hydraulic conductivity, and storage capacity. The 30 years records of piezometric level were used to simulate groundwater depletion and the resulting land subsidence. The results of the geomechanical simulations show that the areas where large differential subsidence developed correspond to the portions of the city where earth fissuring have been observed. The spatial relationship between major withdrawals and the largest simulated subsidence is assessed. © International Congress on Modelling and Simulation, MODSIM 2013.All right reserved.


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