Monitoring wells in clay: the apparently static water level and its influence during variable-head permeability tests

Chapuis, Robert P.; Duhaime, François; Benabdallah, El Mehdi

doi:10.1007/s10064-012-0433-8

Cited by 14 publications

(11 citation statements)

References 43 publications

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“…However, as soon as the effective stresses become lower than the preconsolidation stresses everywhere, the elastic volumetric strain becomes null and ∇ 2 h = 0, which yield a straight derivative graph. As already stated, this new prediction was steadily observed with field slug tests in aquifers, and in soft clays …”

Section: Stress‐strain Solutions For Slug Testssupporting

confidence: 73%

“…Therefore, the stress‐strain conditions for clay predict a curved velocity graph at the beginning of a slug test (irreversible strains), and subsequently a straight line when the volumetric strain becomes elastic. This curvature is regularly observed with slug tests in clay where it lasts 1 to 2 days for a 1 to 2 month‐long test, and also with pulse tests in aquitards where it lasts during almost all test of duration 1 to 2 hours, long before being proven here using geomechanics.…”

Section: Stress‐strain Solutions For Slug Testssupporting

confidence: 66%

“…After that, the derivative graph is straight, but after a long time, it may also change its shape. The change is due to the long lag time of the response in a clay aquitard, and the resulting reality that a “static” water level in the riser pipe of any monitoring well installed in clay is never a piezometric level …”

Section: Discussionmentioning

confidence: 99%

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Stress and strain fields for overdamped slug tests in aquifer materials, and resulting conservation equation

Chapuis

2017

Num Anal Meth Geomechanics

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Summary Two theories may be used to analyze overdamped variable‐head (slug) tests in aquifer materials. The first theory assumes that the solid matrix strain has a negligible influence. The second theory takes into account some elastic and immediate strain. Something is wrong with these theories because they yield different hydraulic conductivity values. This paper explains what is wrong after establishing the strain‐stress elastic equations for a slug test in 2 ideal conditions: plane strain and spherical symmetry. The equations show that the radial contraction (or elongation) and tangential elongation (or contraction) yield a null volumetric strain. As a result, the conservation is described by the Laplace equation, which is used by the first theory. This first theory is the only one to yield correct solutions. The diffusion equation, with storativity, which is used by the second theory, is physically ill founded for slug tests in aquifers. This new proof scientifically confirms previously raised doubts and experimental proofs that the second theory is ill founded.

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Section: Stress‐strain Solutions For Slug Testssupporting

confidence: 73%

Section: Stress‐strain Solutions For Slug Testssupporting

confidence: 66%

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Stress and strain fields for overdamped slug tests in aquifer materials, and resulting conservation equation

Chapuis

2017

Num Anal Meth Geomechanics

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“…With methods based on a velocity graph, the time derivative in Equation is replaced by a finite difference approximation :

- \frac{S_{inj}}{italicck} \frac{Δ H}{Δ t} + H_{0} = H_{normalm}

where H m is the mean hydraulic head for the time interval Δ t and H 0 is the piezometric error, a term added to Equation to acknowledge that the hydraulic head difference between the MW and the aquitard is not known a priori. For a MW installed in an aquitard, the initial ‘static’ water level always lags behind the real hydraulic head, which prevails in the aquitard . With the velocity graph method, H 0 , the difference between the real and apparent H values, can be estimated from the y ‐intercept of a plot of H m on the y ‐axis and Δ H /Δ t on the x ‐axis.…”

Section: Pulse Tests and Their Interpretationmentioning

confidence: 99%

“…Like Equation (16) for the case of radial symmetry and plane strain deformations, matrix equation (Equation (32)) expresses the condition of static equilibrium for the total stress tensor. Equation (33) verifies the mass conservation of water and is thus analog to Equation (1), except that it is not based on a constant total stress hypothesis. Equations (32) and (33) are coupled through the relationship between total stress, effective stress, deformation and pore pressure: effective stress and deformation tensors.…”

Section: Numerical Type Curves For the Case Of A Partially Penetratinmentioning

confidence: 99%

A coupled analysis of cavity and pore volume changes for pulse tests conducted in soft clay deposits

Duhaime

Chapuis

2013

Num Anal Meth Geomechanics

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SUMMARYThis paper presents a new interpretation method for pulse tests, a field permeability test that allows for rapid measurements of hydraulic conductivity k in aquitards. This new method applies to soft clay deposits. To initiate a pulse test, a known volume of water is injected into the sand filter of a monitoring well isolated by a packer. The resulting pressure increase yields an outward movement of the sand filter cavity wall. After presenting the usual interpretation methods and their limits, this paper proposes a new interpretation method based on a coupled analysis of the pressure and displacement fields in the soil using the Biot–Darcy formulation. A series of analytical and numerical non‐dimensional velocity graphs, normalized plots of the mean hydraulic head difference versus its rate of change, are given. For a linear elastic material, these type curves show relatively small variations with the sand filter aspect ratio and the Poisson ratio of the tested clay. The type curves are also found to be independent of the clay compressibility (mv) and k, an important result. A series of pulse tests conducted in a soft marine clay deposit near Montreal, Canada, are interpreted with the proposed method. The hydraulic conductivity values calculated from these tests are closely correlated with independent estimates obtained using long‐duration variable‐head tests. Compared with previous interpretation methods, the proposed method allows soil volume changes to be reconciled with cavity expansion phenomena and the range of type curves available for the interpretation of test data to be constrained. Copyright © 2013 John Wiley & Sons, Ltd.

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A generalized variable-head borehole permeameter analysis for saturated, unsaturated, rigid or deformable porous media

Reynolds

2015

Engineering Geology

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Monitoring wells in clay: the apparently static water level and its influence during variable-head permeability tests

Cited by 14 publications

References 43 publications

Stress and strain fields for overdamped slug tests in aquifer materials, and resulting conservation equation

Stress and strain fields for overdamped slug tests in aquifer materials, and resulting conservation equation

A coupled analysis of cavity and pore volume changes for pulse tests conducted in soft clay deposits

A generalized variable-head borehole permeameter analysis for saturated, unsaturated, rigid or deformable porous media

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