Simulation of Ground Failure Due to Ground Water Pumping by a Three Dimensional FE-IE Model

Poorly-consolidated sedimentary basins in semiarid and arid regions are often subject to intense groundwater withdrawal as this is the only source of the water needed for a regional development. Anthropogenic land subsidence is the usual consequence of water table drawdown and in these areas, e.g., south-western United States, central Mexico, Lybian desert, south Iran, the settlement process is commonly associated to aseismic ground failure consisting of the localized rupture of near surface soils. A number of different mechanisms and conceptual models of fissure generation have been proposed in the literature such as vertical differential compaction, horizontal displacement toward a pumping well, and differential water level decline along a pre-existing fault. Numerical modeling of failure generation and prediction of fissure location, distribution, and geometry is a difficult task. To this aim we use an original modeling approach developed by the authors for the evaluation of the fault influence on land subsidence occurring over depleted gas/oil reservoirs. The geomechanical model is based on the structural equations of poroelasticity solved in a three-dimensional setting by the Finite Element (FE) - Interface Element (IE) approach. While standard FE are used to represent a continuum IE prove especially suited to address the relative displacements of adjacent elements such as the opening and slippage of pre-existing faults or the generation of new fractures. The IE allow for the modelling of fissure/fault mechanics using an elasto-plastic constitutive law based on the Mohr-Coulomb failure criterion. The corresponding FE-IE code is used for the prediction of localized differential subsidence and earth fissure activation/generation with some representative examples discussed in the literature. The results are quite promising and emphasize the potentiality of the proposed computational tool in real-field applications.