A Joint Analytic Method for Estimating Aquitard Hydraulic Parameters.

Area of Science:

• Geosciences
• Hydrogeology
• Geotechnical Engineering

Background:

• Aquitard parameters like vertical hydraulic conductivity (K_v) and skeletal specific storage (S_ske, S_skv) are critical for land subsidence investigations.
• Accurate estimation of these parameters is essential for reliable modeling of subsurface deformation.

Purpose of the Study:

• To develop and present two novel analytic methods for estimating K_v, S_ske, and S_skv of aquitards.
• To apply a joint analytic method combining these techniques to a real-world case study in Shanghai, China.
• To validate the proposed methods by comparing their results with inverse modeling and existing techniques.

Main Methods:

• A delay time ratio concept is used for estimating K_v and S_ske under cyclic hydraulic head changes.
• A second method estimates S_skv based on linearly declining hydraulic heads.
• Both methods utilize analytical solutions for flow within the aquitard and are employed jointly.

Main Results:

• The joint analytic method was applied to a 34.54-m thick aquitard in Shanghai, with deformation data from an extensometer.
• Estimated K_v and S_ske values closely matched those from inverse modeling.
• The proposed method demonstrated superior performance in simulating elastic deformation compared to the stress-strain diagram method.

Conclusions:

• The newly developed joint analytic method is an effective tool for estimating critical aquitard parameters.
• The method provides reasonable initial values for calibrating land subsidence models.
• This approach enhances the accuracy and reliability of land subsidence investigations.