Methods of interpretation of borehole falling-head tests performed in compacted clay liners

2005 ◽  
Vol 42 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Paul Chiasson
Keyword(s):  
Hydraulic Conductivity ◽  
Time Lag ◽  
Past Research ◽  
Quality Assurance Program ◽  
Data Sets ◽  
Compacted Clay ◽  
Clay Liners ◽  
K Value ◽  
Considerable Uncertainty ◽  
Vertical Hydraulic Conductivity

The interpretation of falling-head tests in cased boreholes is discussed. These tests are commonly used to measure hydraulic conductivity of compacted clay liners and are often part of the construction quality assurance program. Three methods of interpretation are reviewed with data sets collected from real tests. Two of these methods have been the subject of past research by other authors: the Hvorslev, or time-lag, method and the velocity method. After the limitations of these two approaches have been underlined, a third method is proposed. It uses a best linear unbiased estimator to fit the theoretical head difference function in a plot of falling water column elevation as a function of time (Z–t method). The Hvorslev method is found unreliable and is not recommended. The velocity method is theoretically sound, but statistical uncertainty can become high when this method is used in testing materials with low hydraulic conductivity, such as clay liners. Materials with low hydraulic conductivity tend to produce scattered velocity plots, creating considerable uncertainty for the estimated k value. The proposed Z–t method is less sensitive to inaccuracies in measurements, yielding a more reproducible result. An interpretation method for stages I and II of two-stage borehole tests is also proposed. This method yields the anisotropy of the liner and the vertical hydraulic conductivity. As a result of inaccuracies in measurements and limited difference between the geometries of stages I and II, the computed anisotropy exhibits significant uncertainty.Key words: clay liners, clay covers, hydraulic conductivity, permeability, in situ test, anisotropy, interpretation.

Remarks on the design of clay liners used in lagoons as hydraulic barriers

1992 ◽  
Vol 29 (3) ◽  
pp. 512-515 ◽  
Author(s):  
S. Leroueil ◽  
J. P. Le Bihan ◽  
R. Bouchard
Keyword(s):  
Hydraulic Conductivity ◽  
Key Words ◽  
Water Content ◽  
Compacted Clay ◽  
Plastic Limit ◽  
Clay Liners ◽  
Natural Soils ◽  
Compacted Clay Liner ◽  
Compacted Clays ◽  
Hydraulic Barriers

Considering that (i) the hydraulic conductivity of compacted clays is smaller on the wet side of optimum; (ii) the plastic limit is the water content below which the soil develops fissures under small stresses; (iii) the plastic limit and the optimum standard Proctor water content are similar for many natural soils; and (iv) the strength of compacted clays, thus the limit of trafficability, is a function of (w – wopt)/Ip, relevant conditions for the design of clay liners and the evaluation of their hydraulic conductivity are proposed. Key words : compacted clay, liner, hydraulic conductivity, strength, design.

Evaluation of the hydraulic conductivity of aquitards

1993 ◽  
Vol 30 (5) ◽  
pp. 781-800 ◽  
Author(s):  
R. Kerry Rowe ◽  
Prebaharan Nadarajah
Keyword(s):  
Hydraulic Conductivity ◽  
Field Test ◽  
Diffusion Theory ◽  
Time Lag ◽  
Pumping Test ◽  
Biot’S Theory ◽  
Test Analysis ◽  
Biot's Theory ◽  
Vertical Hydraulic Conductivity ◽  
Different Types

The evaluation of the bulk vertical hydraulic conductivity of an aquitard based on its response to the pumping of an adjacent aquifer is examined using Biot's theory. Consideration is given to the errors in interpretation of the results of pumping tests which arise as a result of the time lag associated with different types of piezometers as well as the length of the piezometer. Factors to allow for correction of these errors are presented. Although these factors are originally developed for isotropic aquitards, they can be used for anisotropic aquitards with appropriate modifications described in the paper. A comparison is made between the results obtained from diffusion theory (as assumed in the development of techniques currently used in practice) and the more rigorous Biot's theory. The application of the technique is illustrated by two examples. Key words : hydraulic conductivity, field test, analysis, pumping test, piezometers, anisotropy.

Effect of freeze–thaw on the hydraulic conductivity and morphology of compacted clay

1993 ◽  
Vol 30 (2) ◽  
pp. 236-246 ◽  
Author(s):  
Majdi A. Othman ◽  
Craig H. Benson
Keyword(s):  
Hydraulic Conductivity ◽  
Three Dimensional ◽  
Compacted Clay ◽  
Clay Liners ◽  
Overburden Pressure ◽  
Thin Sections ◽  
Freeze Thaw ◽  
State Of Stress ◽  
Soil Liners ◽  
Compacted Clays

Several studies have shown that freeze–thaw causes changes in the hydraulic conductivity of compacted clays. Cracks formed by ice lensing and shrinkage cause the hydraulic conductivity to increase. In this paper, changes in hydraulic conductivity are related to changes in morphology. Photographs of thin sections of frozen specimens show that ice lenses form in compacted clay during freezing in a closed system. Photographs also show that similar ice structures are obtained for one- and three-dimensional freezing, which explains why similar hydraulic conductivities are obtained for both conditions. The photographs also show that a significant network of cracks forms in a single cycle of freeze–thaw. With additional cycles, new ice lenses are created and thus the hydraulic conductivity continues to increase. However, after about three cycles the number of new ice lenses becomes negligible and hence further changes in hydraulic conductivity cease. The temperature gradient and state of stress affect morphology and hydraulic conductivity of compacted clays subjected to freeze–thaw. At larger temperature gradients, more ice lenses form and hence the hydraulic conductivity increases. In contrast, application of overburden pressure inhibits the formation of ice lenses and reduces the size of the cracks remaining when lenses thaw. As a result, the hydraulic conductivity is reduced. Key words : compacted clay, hydraulic conductivity, clay liners, soil liners, freeze-thaw, ice lenses, structure.

Statistical analyses of compacted clay landfill liners. Part 1: model development

1994 ◽  
Vol 21 (5) ◽  
pp. 872-882 ◽  
Author(s):  
Scott B. Donald ◽  
Edward A. McBean
Keyword(s):  
Hydraulic Conductivity ◽  
Geometric Mean ◽  
Model Development ◽  
Statistical Analyses ◽  
Compacted Clay ◽  
Clay Liners ◽  
Landfill Liner ◽  
Landfill Liners ◽  
Clay Liner ◽  
Spatial Correlation Structure

The acceptance of compacted clay liners, from a management point of view, has been a source of major concern because of the uncertainty associated with the hydrogeologic properties of the clay. By examining the flux of leachate through the compacted clay liner of a typical engineered landfill, where the hydraulic conductivity of the clay is represented by a stochastic process, an acceptance protocol suitable for compacted clay landfill liners is derived. Determination of the equivalent hydraulic conductivity of the clay liner is accomplished by comparing the flux of leachate through a homogeneous representation of the clay with the flux obtained by Monte Carlo analyses. Acceptance criteria are subsequently developed based on a statistical technique which calculates the confidence limits about a percentile of a probability distribution as well as about the mean of the distribution. For the landfill configuration simulated, the results indicate that the hydraulic conductivity of a compacted clay landfill liner follows a lognormal distribution and exhibits virtually no spatial correlation structure. In addition, for liners exhibiting a geometric mean conductivity of 10−7 cm/s and a standard deviation of 0.3, the geometric mean value is a conservative estimate of the hydraulic conductivity of the clay, provided the liner is constructed in a series of four 150 mm lifts. Key words: clay liners, hydraulic conductivity, statistical analyses, latin hypercube, equivalent hydraulic conductivity.

scholarly journals Vertical hydraulic conductivity of a clayey-silt aquitard: accelerated fluid flow in a centrifuge permeameter compared with in situ conditions

2014 ◽  
Vol 11 (3) ◽  
pp. 3155-3212 ◽  
Author(s):  
W. A. Timms ◽  
R. Crane ◽  
D. J. Anderson ◽  
S. Bouzalakos ◽  
M. Whelan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Centrifugal Force ◽  
Stress Conditions ◽  
K Value ◽  
Geotechnical Centrifuge ◽  
In Situ Conditions ◽  
Clayey Silt ◽  
Vertical Hydraulic Conductivity ◽  
Permeameter Tests

Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, extraction of fuels from strata such as coal beds, and confinement of waste within the earth. Characterizing low or negligible flow rates and transport of solutes can require impractically long periods of field or laboratory testing, but is necessary for evaluations over regional areas and over multi-decadal timescales. The current work reports a custom designed centrifuge permeameter (CP) system, which can provide relatively rapid and reliable hydraulic conductivity (K) measurement compared to column permeameter tests at standard gravity (1g). Linear fluid velocity through a low K porous sample is linearly related to g-level during a CP flight unless consolidation or geochemical reactions occur. The CP module is designed to fit within a standard 2 m diameter, geotechnical centrifuge with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length. At maximum RPM the resultant centrifugal force is equivalent to 550g at base of sample or a total stress of ~2 MPa. K is calculated by measuring influent and effluent volumes. A custom designed mounting system allows minimal disturbance of drill core samples and a centrifugal force that represents realistic in situ stress conditions is applied. Formation fluids were used as influent to limit any shrink-swell phenomena which may alter the resultant K value. Vertical hydraulic conductivity (Kv) results from CP testing of core from the sites in the same clayey silt formation varied (10−7 to 10−9 m s−1, n = 14) but higher than 1g column permeameter tests of adjacent core using deionized water (10−9 to 10−11 m s−1, n = 7). Results at one site were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses within a 30 m clayey sequence in a homogenous area of the formation. Kv sensitivity to sample heterogeneity was observed, and anomalous flow via preferential pathways could be readily identified. Results demonstrate the utility of centrifuge testing for measuring minimum K values that can contribute to assessments of geological formations at large scale. The importance of using realistic stress conditions and influent geochemistry during hydraulic testing is also demonstrated.

Heterogeneity detection in an experimental clay liner

2003 ◽  
Vol 40 (1) ◽  
pp. 149-160 ◽  
Author(s):  
Dominique Guyonnet ◽  
Jean-Christophe Gourry ◽  
Lucien Bertrand ◽  
Nadia Amraoui
Keyword(s):  
Hydraulic Conductivity ◽  
Geophysical Methods ◽  
The Other ◽  
Dipole Mode ◽  
Compacted Clay ◽  
Clay Liners ◽  
Hydraulic Test ◽  
Clay Liner ◽  
Other Hand

In situ hydraulic tests to characterize the field hydraulic conductivity of clay liners used in landfill applications are often positioned randomly. Yet it is well known that the field performance of low permeability clay liners is generally controlled by heterogeneities that may provide preferential pathways for flow. In this paper, an experimental clay liner is investigated in which heterogeneities were incorporated in a controlled fashion. Heterogeneities were embedded within a compacted clay liner at different locations in the plane and at different depths. Heterogeneities of composition were installed by excavating compacted clay at specific locations and replacing it with a more permeable material. Heterogeneities of compaction were introduced by loosely backfilling the clay into the excavations. Two geophysical methods, ground penetrating radar (GPR) and the EM-38 electromagnetic method, were used to examine whether anomalies detected by geophysics were or were not correlated with the precise locations of the heterogeneities. Hydraulic tests were used to characterize the permeability of the intact clay on the one hand and of the heterogeneities on the other hand. Three different in situ hydraulic test methods were used: a pulse test performed in a hand-augered borehole, a sealed single ring infiltrometer test, and a large scale infiltration test (4 m2) that uses a color tracer to detect possible preferential flowpaths. The GPR showed no significant correlation with heterogeneity locations, nor did the EM-38 method when used in the vertical dipole mode. The EM-38 method used in the horizontal dipole mode, showed significant correlation with heterogeneities when they were apparent at the surface. On the other hand, the method did not clearly detect heterogeneities located at depth. There was consistency between the values of hydraulic conductivity obtained from the different hydraulic field and laboratory tests. "Intact" clay hydraulic conductivities were found to lie between 10–10 and 4 × 10–9 m/s, while the hydraulic conductivity of the heterogeneities of composition was approximately 10–7 m/s. The results of this experiment suggest that the EM-38 method may be useful to optimize hydraulic test locations when characterizing clay liners for landfill applications.Key words: clay liner, hydraulic conductivity, heterogeneity.

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