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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : A semi-analytical model on subsidence of a multi-aquifer system
A semi-analytical model on subsidence of a multi-aquifer system
Author : YU-YUN LIN (1) & YIN-JEN CHEN (2)
ABSTRACT
The land subsidence caused by excessive extraction of groundwater is a complex phenomenon due to the complexities of
soils involved. The extraction of groundwater reduces the interstitial water pressure (i.e. drawdown), which means a
transference of stress to the soil skeleton and its subsequent volume reduction (i.e. subsidence). The coupled theory of
Biot provides a full three-dimensional model of mutually interacting drawdown and deformation of soils. However, the
calculation of subsidence based on the full three-dimensional theory will be very time-consuming, especially for a complex
soil system. Our research extends the perturbed equations, which simplifies the coupled equations of Biot to a quasi threedimensional
model, to groundwater flow in a multi-aquifer system. The analysis is carried out based on two small
parameters and , which are the ratio of aquitard to aquifer in hydraulic conductivity, and that in constrained modulus,
respectively. The model considers the effect of gravity and the phreatic aquifer on subsidence. The computation efficiency
of the prediction model is greatly improved by incorporating Laplace transform and numerical Laplace inversion. The
calculated results have been validated by finite element simulations based on Biots theory. Using this model, we analyze
an unconfined two-aquifer system, in which the top aquifer is the phreatic aquifer. Although the pumping locates at the
bottom aquifer, the water releases from the decline of water table in the phreatic aquifer is much more than from the
aquifer and the aquitard. The other study case is a confined four-aquifer system. Our results show that the subsidence can
be largely affected by the slow drainage of a soft aquitard underlying the pumping aquifer in long time.
File Size : 272,776 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 28/08/2015
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