Interpreting pore-water pressure changes induced by water table fluctuations and mechanical loading due to soil moisture changes

2012 ◽  
Vol 49 (3) ◽  
pp. 357-366 ◽  
Author(s):  
Collins Ifeanyichukwu Anochikwa ◽  
Garth van der Kamp ◽  
S. Lee Barbour
Keyword(s):  
Soil Moisture ◽  
Pore Pressure ◽  
Mechanical Loading ◽  
Water Table ◽  
Pressure Response ◽  
Stress Strain ◽  
Near Surface ◽  
Water Table Fluctuations ◽  
Pore Pressure Response ◽  
Pressure Changes

Pore pressures within saturated subsurface formations respond to stress changes due to loading as well as to changes in pore pressure at the boundaries of the formation. The pore-pressure dynamics within a thick aquitard in response to water table fluctuations and mechanical loading due to soil moisture changes have been simulated using a coupled stress–strain and groundwater flow finite element formulation. This modelling approach isolates the component of pore-pressure response of soil moisture loading from that caused by water table fluctuations, by using a method of superposition. In this manner, the contributions to pore-pressure fluctuations that occur as a result of surface moisture loading (e.g., precipitation, evapotranspiration) can be isolated from the pore-pressure record. The required elastic stress–strain properties of the aquitard were obtained from the measured pore-pressure response to barometric pressure changes. Subsequently, the numerical simulations could be calibrated to the measured response by adjusting only the hydraulic conductivity. This paper highlights the significance of moisture loading effects in pore-pressure observations and describes an efficient technique for obtaining in situ stress–strain and hydraulic properties of near-surface aquitards.

Pore pressure response of seabed in standing waves and its mechanism

2014 ◽  
Vol 91 ◽  
pp. 213-219 ◽  
Author(s):  
Hu Wang ◽  
Hong-jun Liu ◽  
Min-sheng Zhang
Keyword(s):  
Pore Pressure ◽  
Standing Waves ◽  
Pressure Response ◽  
Pore Pressure Response

scholarly journals Preliminary results of pore pressure profiling on theTęgoborze-Just landslide

2018 ◽  
Vol 66 ◽  
pp. 02001 ◽  
Author(s):  
Jacek Stanisz ◽  
Zenon Pilecki
Keyword(s):  
Pore Pressure ◽  
Degree Of Saturation ◽  
Flow Paths ◽  
Near Surface ◽  
Preliminary Results ◽  
Water Conditions ◽  
Landslide Processes ◽  
Pressure Changes ◽  
Variable Water ◽  
Weak Zones

In this study, we present the preliminary results of deep profiling of pore pressure in the near surface formations of the Carpathian flysch, on the Tęgoborze-Just landslide near Nowy Sącz in Southern Poland. The aim of the study is to identify zones with significant changes in pore pressure influenced landslide processes. These pore pressure changes correspond to a greater change in the degree of saturation or water flow paths. Profiling was performed in four series using a CPTU static probe with a NOVA Acoustic cone. The measurement of pore pressure in flysch formations is very complicated due to the strong heterogeneity of the medium properties and variable water conditions, which are strongly influenced by the intensity of precipitation. The tests were carried out in a colluvium to a depth of approx. 5.0 m, i.e. to the border of a less weathered bedrock, under varying water conditions. The results obtained indicate the presence of four zones of significant changes in pore pressure. The location of these zone is consistent with the location of the greater displacement measured with the inclinometer. There is a greater probability that these weak zones may form a rupture surface.

A review of specific storage values from pore pressure response to passive in situ stresses: Implications for sustainable groundwater management

2020 ◽  
Author(s):  
Wendy A Timms ◽  
M Faysal Chowdhury ◽  
Gabriel C Rau
Keyword(s):  
Groundwater Management ◽  
Pore Pressure ◽  
Pressure Response ◽  
Earth Tides ◽  
Low Permeability ◽  
Specific Storage ◽  
Sustainable Groundwater Management ◽  
In Situ Stresses ◽  
Pore Pressure Response

<p>Specific storage (S<sub>s</sub>) values are important for analyzing the quantity of stored groundwater and for predicting drawdown to ensure sustainable pumping. This research compiled S<sub>s</sub> values from multiple available studies based on pore pressure responses to passive stresses, for comparison and discussion with relevant poroelastic theory and groundwater applications. We find that S<sub>s</sub> values from pore pressure responses to passive in situ stresses ranged from 1.3x10<sup>-7</sup> to 3.7x10<sup>-5</sup> m<sup>-1</sup> (geomean 2.0x10<sup>-6</sup> m-1, n=64 from 24 studies). This large S<sub>s</sub> dataset for confined aquifers included both consolidated and unconsolidated strata by extending two recent literature reviews. The dataset included several passive methods: Individual strains from Earth tides and atmospheric loading, their combined effect, and values derived from soil moisture loading due to rainfall events. The range of S<sub>s</sub> values spans approx. 2 orders of magnitude, far less than for hydraulic conductivity, a finding that has important implications for sustainable groundwater management. Both the range of values and maximum S<sub>s</sub> values in this large dataset were significantly smaller than S<sub>s</sub> values commonly applied including laboratory testing of cores, aquifer pump testing and numerical groundwater modelling. </p><p>Results confirm that S<sub>s</sub> is overestimated by assuming incompressible grains, particularly for consolidated rocks. It was also evident that Ss that commonly assumes uniaxial conditions underestimate S<sub>s</sub> that accounts for areal or volumetric conditions.  Further research is required to ensure that S<sub>s</sub> is not underestimated by assuming instantaneous pore pressure response to strains, particularly in low permeability strata. However, in low permeability strata S<sub>s</sub> could also be overestimated if based on total porosity (or moisture content) rather than a smaller free water content, due to water adsorbed by clay minerals. Further evaluation is also required for influences on S<sub>s</sub> from monitoring bore construction (ie. screen and casing or grouting), and S<sub>s</sub> derived from tidal stresses (undrained or constant mass conditions) that could underestimate S<sub>s</sub> applicable to groundwater pumping (drained or changing mass conditions). In summary, poroelastic effects that are often neglected in groundwater studies are clearly important for quantifying water flow and storage in strata with changing hydraulic stress and loading conditions. </p>

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