Prediction Method Of Deformation Of Aquifer Induced By Variation Of Seepage Environment

This study was undertaken to evaluate the deformation of aquifer caused by variationof groundwater seepage environment. In order to investigate the mechanism of thesephenomenons, theoretical analysis, laboratory element tests and numerical simulationswere conducted to analysis deformation found in aquifer. The modified model based onCosserat continuum mechanism was proposed; the variation of seepage environment wasdiscussed in laboratory tests; the modified model was employed to investigate the largedeformation of Aquifer IV in Shanghai and surface settlement in Changzhou. The gist andprimary new findings of this dissertation induces:1) One of the main reason causing deformations in aquifer was accumulation of shearstress in aquifer. By considering the scale of soil element, the Cosserat continuummechanism could be applied to calculate the deformantion of aquifer.2) A modified model based on Cosserat continuum mechanism was proposed in thisstudy. Budhu and Adiyaman first proposed a model to simulate the deformation ofunconfined aquifer. In this model, the simple shear displacement and rotation of soil hasbeen considerated. Due to the different consolidation procedure between confined andunconfined aquifer, a modified model based on Budhu’s model was proposed in this studyto simulate the deformation of confined aquifer. Especially, new simultaneous polynomialequations were used to fit groundwater head with sudden change or in long distance.3) The mechanism of underground structures on the groundwater seepageenvironment was established. A series of laboratory investigation on the disturb behaviorof water pumping and underground constructions in aquifer. The results show thatgroundwater level and equivalent permeability were serious disturbed by water pumpingand underground constructions. According to laboratory tests, the assumption of usingpolynomial to fit groundwater level proposed by Budhu and Adiyaman has been proved asa useful simplifies approach. However, simultaneous polynomial equations were used tofit the groundwater level with sharp variation. The construction of underground structurein aquifer would decrease the equivalent permeability. 4) The calculation method of equivalent permeability of the aquifer was proposed.The pile foundation not only reduced the seepage area, but also enlarged seepage path.With different arrangement, the blocking effect by pile foundation was also different too.5) A series of numerical analysis were conducted to analyze the deformation ofaquifer due to groundwater pumping and underground structures construction found inShanghai and Changzhou. The simulation results were shown below:i) The results of modified model based on Cosserat continuum mechanism fit fielddata very well. Three different models, including modified model, flow model and plainstrain model, were introduced for comparing. The consolidation of overburden layer andaccumulation of shear stress in aquifer were both considered in the modified model. Thesimulating results showed that the hydraulic gradient has large influence on deformationof aquifer.ii) Based on the field test data of Shanghai, the results proved the cyclic loading wasnot the main reason causing aquifer deformation. Due to shallow depth and large thicknessof Aquifer II in Changzhou, the deformation in aquifer already caused large landsubsidence. The simultaneous polynomial equations were more suitable in water levelfiting for long distance than single equation. The densely constructed undergroundstructures would increase land subsidence.