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Title A coupled stress-flow numerical modelling methodology for identifying pore-pressure changes due to total soil moisture loading
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Date Available
University/Publisher University of Saskatchewan
Abstract This thesis describes a numerical modelling methodology to interpret dynamic fluctuations in pore-pressures to isolate the effects of loading associated with changes in total soil moisture (site water balance) alone. The methodology is required to enhance the data-interpretation and performance-assessment for potential applications of a novel piezometer-based, large-scale, geological weighing lysimeter. This interpretative methodology is based on a method of superimposing computer-based numerical analyses of independent causes of pore-pressure transients to separate the different pore-pressure responses. Finite element coupled load-deformation and seepage numerical models were used to simulate field-observed piezometric responses to water table fluctuations and loading induced by surface water balance (using meteorological data). Transient pore-pressures in a deep clay-till-aquitard arising from variations in the water table within a surface-aquifer were modelled and removed from the measured pore-pressure record (corrected for earth tide and barometric effects) to isolate and identify pore-pressure fluctuations arising from loading associated with site water balance. These estimates were compared to simulated pore-pressure responses to an independently measured water balance using meteorological instrumentation. The simulations and observations of the pore-pressure responses to surface water balance were in good agreement over the “dry” years of a 9-year period. Some periods of significant differences did occur during “wet” years in which runoff, which is not accounted for in the current analyses, may have occurred. The identification of pore-pressure response to total soil moisture loading using the developed numerical modelling methodology enhances the potential for the deployment of the piezometer-based geological weighing lysimeter for different applications which include real-time monitoring of site water balance and hydrological events such as precipitation and flooding. Interestingly, the disparity occurring during the “wet” years even suggests the potential to adapt the method to monitor runoff (net lateral flow). The methodology also demonstrated the capability to accurately estimate in situ elastic and hydraulic parameters. Calibration of the model yielded “equivalent” properties of the aquitard (hydraulic conductivity, Kv, of 2.1E-5 m/day and specific storage, Ss, of 1.36E-5 /m) for a Skempton’s B-bar coefficient of 0.91 for an assumed porosity of 0.26. Sensitivity tests also provided insight into the consolidation and pressure propagation (swelling) behaviour of the aquitard under parametric variations. The parameters obtained are consistent with range of values reported for glacial clay till soil. Therefore, this work also provides a unique case history of a method for determining, large scale, in situ material properties for geo-engineers and scientists to explore by simply using piezometric and meteorological data.
Subjects/Keywords hydraulic conductivity; consolidation; elastic modulus; water balance; barometric correction of pore-pressure; pore-pressure transients
Contributors Barbour, S. Lee; van der Kamp, Garth; Samarasekera, Lal; Haug, Moir; Bashir, Rashid; Reeves, Malcom
Language en
Country of Publication ca
Record ID handle:10388/etd-04122010-220038
Other Identifiers TC-SSU-04122010220038
Repository sask
Date Retrieved
Date Indexed 2018-12-06

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…piezometer. The goal of this work is to establish a method of interpreting the pore-pressure dynamics for a geological weighing lysimeter when there are additional pore-pressure transients caused by groundwater flow transients. The general approach will be…

…6 2.2 Instantaneous Pore-pressure Response to Surface Mechanical Load ..................... 7 2.2.1 Mechanism and Observation of Instantaneous Pore-pressure Response ............ 8 2.2.2 Quantification of the Instantaneous Excess Pore-pressure

…8 2.3 Weighing Lysimeter-Interpretations of Pore-pressure Changes ............................ 9 2.4 Treatment of Transient Flow Effects with Consolidation Theory ........................ 11 2.5 Numerical Modelling for Rigorous Analysis of the…

…Response and Processing of Site Pore-pressure Data ........... 23 3.6.2 Observed Aquitard-Piezometer Hydraulic Head Changes ............................... 25 4 CHAPTER 4 – THE NUMERICAL MODELLING PROCESS............................. 27 4.1 The Modelling…

…Application of Modelling to “Weighing Lysimeter” Interpretation ..................... 71 4.6.1 Modelled Aquitard-Piezometer Response to Water Table Fluctuations........... 72 4.6.2 Observed Aquitard Pore-pressure Response to Total Soil Moisture Changes . 72 5…

…generating hydraulic boundary condition for the numerical modelling Old Aspen Site problem (1998 – 2006) ....... 23 Figure 3.8: Barometric effect and its correction on pore-pressure head changes from which Skempton's (B-bar) of 0.91…

…was determined (at the depth of 34.6m for Old Aspen Site): (i) Observed pore-pressure head changes corrected only for earth tide; (ii) Observed barometric pressure head change x 0.91; and (iii) Porepressure head…

…and hydraulic (hw(t) or qz (or qx)) boundary conditions .................................................................................................. 49 Figure 4.4. Modelled Pore-pressure change (degree)…

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