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Numerical Modelling of Land Subsidence Induced by Groundwater Extraction in Aquifers, Considering the Unsaturated Effects and Using the Element-Free Galerkin Method

Tourei, Ahmad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54199 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Land subsidence is one of the consequences of groundwater withdrawal. This phenomenon can cause cracks in the surrounding structures, balance out the foundation of bridge piers, damage to roads, pipelines, etc. The main goal of this study is to provide a coupled flow-deformation model capable of simulation of land subsidence associated with groundwater extraction in unsaturated isotropic and true anisotropic aquifer systems, using the element-free Galerkin (EFG) method. Using this model and based on the geological features of an aquifer, we can easily forecast the hydraulic head change and land subsidence in different places and times during groundwater pumping. According to the current catastrophe of water shortage in Iran, this model will hopefully help us consider land subsidence more efficiently before we plan to extract groundwater in any field. After the numerical formulation was provided and a few benchmark problems were modeled, the hydromechanical model is used to simulate an unsaturated isotropic and anisotropic aquifer system with a single pumping well to see the hydraulic head change and land subsidence in the field and compare the results with the Finite Element Method. The results were quite satisfying, and the EFG method's results in the first hours were more reasonable than FEM's results. Finally, to observe the effect of the aquifer's hydraulic conductivity, elastic modulus, Poisson ratio, initial porosity, and also water pumping rate, a parametric study has been done to understand each parameter effect on land subsidence and hydraulic head decline. The results show that the elastic modulus, Poisson ratio, initial porosity, and water pumping rate impact the ultimate land subsidence. Therefore, it is needed to consider these parameters as much accurately as possible to control land subsidence. Moreover, it was observed that by ignoring the unsaturated parameters and performing saturated analysis, the final subsidence was approximately 70 percent more than the final subsidence considering the unsaturated parameters. Thus, it is necessary to consider unsaturated parameters in unsaturated aquifers to get the most accurate results
  9. Keywords:
  10. Numerical Modeling ; Element Free Galerkin Method (EFGM) ; Land Subsidence ; Groundwater ; Anisotropic Aquifers ; Unsaturated Aquifers ; Coupled Flow-Deformation Analysis ; Groundwater Extraction

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