Rigid-wall Permeameter Research Articles

Internal instability of cohesionless soils in upward and downward flow: an experimental verification of theory

Rigid-wall permeameter testing of two potentially unstable gradations established that the critical hydraulic gradient to trigger instability is smaller for upward flow than for downward flow. The experimental finding is explained with reference to the Skempton-Brogan stress reduction factor α in the finer fraction content of the soil. Theory uses the α-factor to define a hydro-mechanical envelope in gradient-stress space that is independent of flow direction, and the experimental results are found to be in good agreement with the theory. Testing with upward flow is recommended to determine the value of α for an internally unstable gradation because, in contrast to downward flow, there is no requirement for an outflow boundary.

Large Permeameter for Continuing Erosion Filter Tests

Abstract The Continuing Erosion Filter (CEF) test and criteria were developed by Foster and Fell to assess severities of internal erosion of an existing embankment dam whose filter does not satisfy modern filter design criteria developed by Sherard and Dunnigan. Those criteria were developed from laboratory tests on materials that may not be directly applicable to the widely graded filter materials. To address this issue, a large diameter (300 mm) rigid-wall permeameter was constructed to assess the internal erosion of zoned embankment dams constructed of widely graded filter materials. The large permeameter allows for testing of embankment dam fill materials up to a maximum particle size of 37.5 mm. A commissioning test program was conducted to verify the test equipment and testing methodology used in this study. Two CEF test results from the test program are reported in this paper to demonstrate the novel features of the permeameter cell design and its test setup. These features include a split-cell design for ergonomic function, real-time outflow rate measurement, inflow and filter specimen water pressure measurements, and erosion loss measurement. A wet method to estimate erosion loss was proposed as an alternative to the traditional oven-drying method.

Scalp-and-Replacement of Oversize Particles: Laboratory Permeameter Testing

Abstract A reanalysis is made of 24 rigid-wall permeameter tests on eight widely-graded sand-gravel mixtures, using empirical methods that post-date the original study by Jones in 1955. The reanalysis is conducted to better understand the consequences of the scalp-and-replacement method of removing oversize particles in laboratory permeameter testing. A necessary requirement of the scalp-and-replacement method is that the porosity, hydraulic conductivity, and susceptibility of the test gradation to internal instability be largely unchanged. The reanalysis provides a framework for such considerations and serves to identify the consequences of excessive scalping such as increased porosity and hydraulic conductivity. The results show that scalp-and-replacement to 35 % of the gradation curve imparts no significant change to the porosity and hydraulic conductivity of an internally stable gradation.

Predicting Hydraulic Conductivity for Flexible Wall Conditions Using Rigid Wall Permeameter

The hydraulic conductivity is known as the soil properties that mostly vary over an order of magnitude. There are many laboratory test methods to determine the hydraulic conductivity of the soil. Each test has its own merits, drawbacks and limitations. One of these methods is the measurement using a rigid wall permeameter (RWP), which is a common practice to obtain the fluid transmissibility characteristics of the soil matrix. This type of permeameter has the advantages of low cost, simplicity of test equipment, and adaptability to many different types of permeant liquids. Another method is the measurement through a flexible wall permeameter (FWP). The hydraulic conductivity measured using the FWP is conducted in a confined cylinder in which water flow is forced into one direction. The main disadvantage of this type is being relatively more expensive and needs more time to perform the test compared to the RWP. This study is aimed at comparing three testing conditions to obtain an adjustment factor for the hydraulic conductivity test normally carried out in practice in order to cut down the time needed to perform the test as well as its cost. Different mixtures of sand and expansive clay addition were considered to examine the effect of expansive clay content on the values of the hydraulic conductivity. Tests results revealed that the clay content had a significant effect on the swelling potential, which was attributed to structural changes in the mixtures. The hydraulic conductivity of mixtures decreases with the increase in clay content. The hydraulic conductivity of mixtures tested using FWP was observed to be lower than that of mixtures tested using RWP at similar clay contents. The tests conducted enabled establishing a correction factor to adjust the hydraulic conductivity normally obtained in practice using rigid wall cells.

On Preferred Saturation Methods for Geotechnical Flow Tests

Abstract Laboratory flow tests performed on granular materials in rigid-wall permeameters are used to determine the hydraulic conductivity of saturated materials or to study particle migration. For such tests, specimen preparation is important, particularly the saturation process. The presence of gas bubbles in the tested specimen leads to smaller hydraulic conductivity values and may affect particle migration. Therefore, measures must be taken to obtain fully saturated specimens. In order to improve saturation, two elements have to be taken into consideration: first, the presence of gas in the permeant water; second, the presence of gas in the pores of the specimen. Several flow tests are described in ASTM standards. These standards involve different conditioning methods for permeant water (e.g., heating, seepage through a sand filter, cavitation under vacuum), and different specimen saturation methods (e.g., saturation with an upward flow under vacuum, following carbon dioxide flushing). In this article, water deaeration and specimen saturation methods were evaluated and compared using a mass-volume method. In the first phase, the importance of using deaerated permeant water was examined by comparing different conditioning methods for permeant water. Saturation using water in equilibrium with atmospheric pressure was compared with saturation with water heated at 40°C, water deaerated using a sand filter, and water deaerated by cavitation under vacuum. In the second phase, the influence of purging the gas contained in the soil specimen before saturation using carbon dioxide or a vacuum was compared. In both cases, the permeant water was deaerated by cavitation under vacuum. These tests showed that combining a purge of the specimen with carbon dioxide with saturation using an upward flow of water deaerated by cavitation under vacuum yielded the highest degree of saturation for granular specimens in a rigid-wall permeameter. Another advantage of this combination is that it accelerates specimen saturation.

Effect of Confining Conditions on the Hydraulic Conductivity Behavior of Fiber-Reinforced Lime Blended Semiarid Soil.

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (ksat) were determined. For FC fibers, an increase in fiber dosage caused ksat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, ksat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained.

Internal Erosion of a 0–5 mm Crushed Sand in a Rigid Wall-Permeameter: Experimental Methods and Results

The article deals with internal erosion in 0–5 mm crushed sand, a material used in urban facilities. Several methods, designed for natural materials, predicted a risk of internal erosion for the crushed sand. The real risk was evaluated in clear-wall, watertight and airtight, rigid-wall permeameters with lateral piezometers. Each test started with a fully saturated specimen, verified by a mass-and-volume method. In their initial condition, the specimens were homogeneous, as directly confirmed by three methods. Each erosion test included successive seepage steps at a constant mean gradient. Migration of fine particles was observed through the clear wall. Dyed water colored three or four preferential seepage paths inside the specimen, not along the wall, confirming that the preparation method was correct. The predictive methods correctly forecast the size of mobile particles but overestimated the gradient that triggered the internal erosion process. The tests were the first ones to include nonreactive tracer tests, which gave the effective porosity value at different gradient steps. This value decreased with internal erosion, a novel result, which quantified the fact that more seepage concentrated in preferential seepage paths. Nonreactive tracer tests can thus be used to quantify the formation of preferential seepage paths.

Stiffness, compressibility, and hydraulic conductivity of compacted soil mixtures submitted to acidic percolation

Abstract The inadequate disposal of hazardous solid waste has become a potential issue, mainly because of the impacts on the environment and human health. This occurs mainly through the contamination of subsurface soil and groundwater by leachates, which are often of the acidic constitution. To prevent such situations, the study of more efficient waste containment techniques has become opportune. In this way, this work was aimed to investigate the mechanical and hydraulic behavior of compacted clayey soil, with and without the addition of Portland cement (0 and 2%), submitted to the action of a sulfuric acid solution (2% volume concentration) and to a constant static vertical load (280 kN/m2), aiming at its prospective application as containment barrier. The experimental program comprised a few tests performed in an instrumented rigid-wall permeameter, during which the variations in hydraulic conductivity, shear modulus, and settlements were measured. The results showed that the hydraulic conductivity increased with cement addition when only water was percolated. During the acidic percolation, however, a reduction was observed only for the cemented soil. The acidic attack caused, almost instantaneously, an increase in the settlement rate and a reduction in stiffness, although a trend of stabilization was observed afterward.

Predicted and measured hydraulic conductivity of sand-sized crushed limestone

The hydraulic conductivity of 54 sand-sized crushed limestone materials was measured by conducting constant head tests in a rigid-wall permeameter and was estimated using six predictive equations requiring easily obtainable parameters. The gradations tested had effective grain size, D10, from 0.079 to 2.15 mm; uniformity coefficient, Cu, from 1.19 to 15.79; and void ratio, e, from 0.42 to 0.76. The measured hydraulic conductivity had a range of about three orders of magnitude (3.4*10−3 to 3.3 cm/s). Four of the predictive equations, based on the square of the effective grain size, D102, yielded closely grouped results differing by not more than a factor of 2. Long existing equations by Terzaghi (1925) and by Hazen (1892), adjusted for void ratio according to Taylor (1948), were found to have a high predictive efficiency with a ratio of predicted to measured values between 1/2 and 2 for 70% of the materials tested. The Kenney et al. (1984) equation, based on D52, was also efficient but underestimated measured values for 63% of all cases. The Kozeny–Carman equation (Taylor 1948; Chapuis 2012), based on specific surface, overestimated measurements for 90% of the tested materials by a factor of up to 3.

Development of a novel base liner material for offshore final disposal sites and the assessment of its hydraulic conductivity

In the process of landfilling, leachates resulting from the waste landfill are likely to cause secondary environmental pollution, and installation of a basal liner is essential under a landfill site to block and reduce permeation of leachate flowing into the subsurface environment. The research aims to develop a salt-resistant bentonite and a novel base liner material for offshore waste disposal. The liner materials consist of core materials and coating materials in which mixtures of bentonite, sepiolite, and guar gum were used to overcome the shortcomings in bentonite to realise a high water-resistance and a permeability coefficient of below 1.0 × 10−7 cm/s under saline water conditions. The optimal mixing ratio of bentonite, sepiolite, and guar gum was confirmed as 76:19:5 by conducting drying shrinkage cracking tests, free swelling tests, and hydraulic conductivity tests. The hydraulic conductivities of spherical particles, as measured in a rigid-wall permeameter and a flexible-wall permeameter, were less than 1.0 × 10−7 cm/s under saline water conditions. The compressive properties of spherical particles were evaluated through triaxial compression testing. The engineering characteristics of the liner material were studied in the present research, but the long-term biodegradation characteristics of polymer additives were also important, yet remained unclear. The long-term biostability of the additives, and its effect on basal liner performance should be evaluated in future research.

How to Improve the Quality of Laboratory Permeability Tests in Rigid-Wall Permeameters: A Review

ASTM D2434, Standard Test Method for Permeability of Granular Soils (Constant Head) (Withdrawn 2015), and ASTM D5856, Standard Test Method for Measurement of Hydraulic Conductivity of Porous Material Using a Rigid-Wall, Compaction-Mold Permeameter, are used to measure the saturated hydraulic conductivity, Ksat, of soil specimens in rigid-wall permeameters (RWPs). Several laboratory conditions and settings explain why the tests do not give Ksat values but unsaturated hydraulic conductivity, K(Sr), values for a degree of saturation, Sr, that is often in the 80–85 % range. It is suggested to improve ASTM D2434 and ASTM D5856 by adding two requirements: (1) use a watertight-and-airtight RWP (a control method is provided), and (2) use a mass-and-volume method to obtain the true Sr value of the tested specimen. To illustrate potential detrimental impacts of current standards, the article describes a case where sand was planned to be used as a filter layer for a solid waste project. Large quantities of sand had been delivered at the construction site. The Ksat value of the sand, as compacted, had to exceed 10−4 m/s to satisfy a bylaw. To prove this, two laboratories followed ASTM D2434 for their tests but found K values of 5−8 × 10−5 m/s. The project engineers asked the authors to make verifications. The prior tests were redone and yielded similar K values. However, it was found that the real Sr value was close to 80 % instead of being assumed to be 100 %. Other tests were performed after using vacuum and deaired water in a watertight-and-airtight permeameter: the specimens reached Sr = 100 % and gave Ksat values of about 2 × 10−4 m/s, 3–4 times higher than initial tests. As a result, the already delivered sand satisfied the bylaw condition and there was no need to return large quantities of sand already delivered, to purchase a new type of sand after having done laboratory tests, and to have a time delay in construction, all these items having a high economic impact.

Assessing internal erosion with the modal decomposition method for grain size distribution curves

The modal decomposition method (MDM) is used to analyse the grain size distribution curve (GSDC) of a soil that was likely to produce internal erosion according to old criteria, and produced internal erosion in laboratory tests. Many previous studies have assumed that such a soil contains a coarse fraction and a fine fraction, the latter being able to migrate within the pores of the coarse fraction. It is shown here that the tested soil had not two fractions, but three grain size modes according to the MDM. The soil was tested in a rigid-wall permeameter under downward seepage. After the experiment, the specimen was divided into four parts, using the lateral piezometers positions to define the parts. The same three grain size modes (same means and variances) were found in the GSDCs of the four parts. In addition, the MDM could quantify internal erosion. The upper part of the specimen had lost the fine mode and had the highest proportion of coarse mode, whereas the medium-mode percentage had little variation with depth. This example explains how the modal decomposition method may help to quantify internal erosion.

Geotechnical properties of municipal solid waste at Laogang Landfill, China

Landfills have been widely constructed all around the world in order to properly dispose municipal solid waste (MSW). Understanding geotechnical properties of MSW is essential for the design and operation of landfills. A comprehensive investigation of geotechnical properties of MSW at the largest landfill in China was conducted, including waste composition, unit weight, void ratio, water content, hydraulic conductivity, and shear behavior. A large-scale rigid-wall permeameter and a direct-shear apparatus were adopted to test the hydraulic conductivity and shear behavior of the MSW, respectively. The composition of the MSW varied with age. With the depth increasing from 0 to 16m, the unit weight increased from 7.2 to 12.5kN/m3, while the void ratio decreased from 2.5 to 1.76. The water content ranged between 30.0% and 68.9% but did not show a trend with depth. The hydraulic conductivity of the MSW ranged between 4.6×10−4 and 6.7×10−3cm/s. It decreased as the dry unit weight increased and was sensitive to changes in dry unit weight in deeper layers. Displacement-hardening was observed during the whole shearing process and the shear strength increased with the normal stress, the displacement rate, and the unit weight. The friction angle and cohesion varied from (15.7°, 29.1kPa) to (21.9°, 18.3kPa) with depth increasing from 4 to 16m. The shear strength of the MSW obtained in this study was lower than the reported values in other countries, which was caused by the less fibrous materials in the specimens in this study. The results in this study will provide guidance in the design and operation of the landfills in China.

Investigation of the Effect of Different Saturation Methods on the Undrained Shear Strength of a Clayey Soil Compacted with Standard and Modified Proctor Energies

In this study, unconsolidated-undrained (UU) shear strengths of a clayey soil that is subject to saturation separately by using vacuum saturation method and falling head method were investigated. In the study, a soil with CL class according to Unified Soil Classification System was used. The soil samples prepared by being compacted in a rigid-wall permeameter mechanism were subject to a saturation process for periods varying from 1 week to 4 weeks. In the saturation by using falling head method, maximum 4m hydraulic load was applied to the samples. In saturation by using vacuum method, minimum - 70 kPa vacuum was used. After the saturation process, the samples were subject to UU type triaxial tests. Depending on the saturation method and duration, a decrease of approximately 2 - 3 times was observed in UU shear strength parameters (c u and ϕ u ) of the samples, which are subject to the saturation process, compared to the unsaturated samples. In the samples compacted with Standard Proctor Energy (SPE), strength parameters obtained under vacuum for one week were lower compared to samples saturated for 4 weeks by using the method of saturation by gravity. In the samples compacted with Modified Proctor Energy (MPE), vacuum method did not give a successful result.

Experimental and numerical modeling of chemical osmosis in the clay samples of the aquitard in the North China Plain

This study focuses on addressing the existence of chemical osmosis in the clay samples of the aquitard in the North China Plain (NCP). For this purpose, chemical osmotic experiments in the clay samples collected from the aquitard in the NCP were implemented to estimate the reflection coefficient or chemico-osmotic efficiency in clayey sediments. More specifically, under a certain chemical potential gradient, the reflection coefficients were, respectively, achieved by measuring the osmotic flow and the induced pressure in terms of the two sets of undisturbed clay core samples and their remolded clay samples equipped in a rigid wall permeameter. The measured reflection coefficient is the value of 0.023 for in situ clay sample, much smaller than that of 0.098 for remolded sample. Also, the constant-head tests for determining the hydraulic conductivity of clay samples were conducted before and after the osmotic tests. It is indicated that the permeability of the remolded sample is smaller than the undisturbed sample in both periods. Moreover, a chemical osmosis continuum model was used to fit the evolution of the osmotically driven hydraulic pressure in the clay samples where more intrinsic parameters of the samples were calibrated. Additional analysis demonstrates the sensitivity of the osmosis pressure to the different parameters input to the model for the in situ clay sample. This study could provide a reliable basis for further evaluating the role of clay sediments in the desalination of shallow saline groundwater and salinization of deeper fresh groundwater in the NCP.

Flow rate measurement in undamaged multicomponent geosynthetic clay liners

ABSTRACT: The objective of the paper is the presentation of a test method to quantify advective flow rates through multicomponent geosynthetic clay liners (GCLs). A procedure was developed, combining measuring devices from EN 14150 for flow rate measurement through geomembranes and a rigid wall permeameter from NF P 84-705 aiming at measuring the flow rates through GCLs. Multicomponent GCLs by structure fall between geomembranes and GCLs. The resulting testing device allows measurement of very small variations of volume with time while applying constant hydraulic pressures. The pressure difference applied on both sides of the multicomponent GCL specimens varied between 25 kPa and 100 kPa, the latter value being equal to that applied across geomembranes in EN 14150, except in one case where the multicomponent liner had a light coating. In this case hydraulic heads of 0.3 and 0.6 m were applied. Four different multicomponent GCLs were tested, from three different manufacturers, in order to determine the ability of the testing equipment to quantify the flow rate through multicomponent GCLs. The flow rate measurement was performed after a hydration phase under a very low hydraulic head and a 10 kPa normal load on the specimens in accordance with NF P 84-705. Details are given of the experimental conditions that might lead to the development of a standard for the measurement of flow rates through multicomponent GCLs. Results obtained tend to show that flow rates are one order of magnitude larger than those usually measured for virgin geomembranes, that is 10–5 m3/(m2 d), except for one of the multicomponent GCLs for which the light coating resulted in larger flow rates, measured with hydraulic heads of 0.3 and 0.6 m. In this case values consistent with previous values from the literature in the range 1.4 × 10–11 m/s to 2.2 × 10–11 m/s were obtained.

Evaluation of the Permeability Behaviour of Sand-Bentonite Mixtures Through Laboratory Tests

In recent years, when suitable impervious soils are not available for containing the waste, barriers constructed using sand-bentonite mixtures are being frequently adopted to contain the waste. This paper presents the laboratory evaluation of permeability of sand-bentonite mixtures through falling head tests performed with rigid wall permeameter and oedometer on different categories of sand-bentonite mixtures. Five different categories of sand-bentonite mixtures were formulated by varying bentonite content in increments of 5 % from 5 to 25 % by dry weight. Atterberg limits and compaction characteristics of sand-bentonite mixtures were evaluated. With an increase in bentonite content, the unconfined compressive strength of the sand-bentonite mixture was found to increase linearly and a sharp decrease in permeability was registered up to a bentonite content of 15 % and beyond this the decrease in the permeability was marginal. Permeability tests were carried out with and without prior saturation of the samples. It was found that permeability behavior of sand-bentonite mixtures was affected by the initial saturation process and type of permeability testing method.

A new theoretical method to evaluate the internal stability of granular soils

The geotextile filter design is particularly complex when granular base soils are internally unstable. In these conditions, the design criteria available in literature are not always reliable. This paper deals with a new theoretical method developed to evaluate the internal stability of granular soils. To simulate, theoretically, the filtration process inside these soils, a set of spherical particles and different soil relative densities have been considered. The soil has been represented by means of a sequence of parallel layers, containing constrictions and particles, placed upon each other at a distance, in the direction of hydraulic flow, which is a function of the soil relative density. The movement of the fine particles through the different soil layers has been simulated by means of a mechanism that compares each particle contained in the i layer with the constrictions contained in the next i + 1 layer. The results of the numerical simulations were used to evaluate the internal stability of the analyzed granular soil and the corresponding critical diameter of suffusion, Dc. Finally, the reliability of the proposed theoretical method was evaluated by means of the results of experimental long-term filtration tests performed using a rigid-wall permeameter on different unstable granular soils.

벤토나이트-해포석-구아검 혼합물질이 코팅된 제강슬래그의 해수에 대한 투수성 평가

Bentonite has been generally used as vertical cutoff barrier material and reported to have several problems regarding its low workability, drying shrinkage cracking by particle cohesion, and ineffective waterproof ability under sea water condition. In this study, the particle sealant, the furnace slag coated by the mixture of bentonite, sepiolite and guargum, was developed to compensate these weak points and the hydraulic conductivity of the particle sealant was evaluated. Drying shrinkage cracking and swelling index was estimated to find the optimal mixing ratio of bentonite, sepiolite and guargum. The hydraulic conductivity of the particle sealants having different amount of sealant (bentonite-sepioliteguargum mixture) coating the furnace slag was estimated using the rigid wall permeameter and flexible wall permeameter. The results showed that drying shrinkage cracking was not found in the bentonite-sepiolite mixture with 20% sepiolite contents and the results from free swelling tests for the sealant having 1 : 0.025, 1 : 0.05 and 1 : 0.075 of weight ratios of bentonite-sepiolite mixture and guargum under simulated sea water condition were higher than those for the bentonitesepiolite mixture without guargum under tap water condition. These three sealants were coated on the furnace slag with 50% and 60% of sealant in the particle sealant and the hydraulic conductivity was estimated. In the cases of the particle sealants having 20% sepiolite in the bentonite-sepiolite mixture and 1 : 0.075 weight ratio of the bentonite-sepiolite mixture and guargum, the hydraulic conductivity from the rigid wall permeameter was below <TEX>$1.0{\times}10^{-7}$</TEX> cm/sec under simulated sea water condition. The hydraulic conductivity of the particle sealant having <TEX>$1.0{\times}10^{-6}$</TEX>~<TEX>$1.0{\times}10^{-7}$</TEX> cm/sec by the rigid wall permeameter was estimated using the flexible wall permeameter and found to be below <TEX>$1.0{\times}10^{-7}$</TEX> cm/sec.

Hydraulic Conductivity Determination of Compacted Sand-Bentonite Mixture Using Filter Press

Abstract This paper presents a method to adapt a measurement in order to enhance its exploitation time and provide a suitable comparison with standard permeability tests. The filter press apparatus used for the fluid loss test (FLT) was selected to elaborate a hydraulic performance method, which is used for compacted sand-bentonite mixtures. An analytical method was developed for hydraulic conductivity determination. Material and test parameters (hydraulic pressure Po, hydraulic gradient i, hydraulic conductivity ko, and α coefficient) were highlighted. Series of experiments were performed with a filter press and rigid wall permeameter (RWP). The hydraulic study was performed on samples composed of soil with 2 %, 3.5 %, and 5 % of an activated Ca-bentonite permeated with a weakly 1×10−3 M NaCl. An improved FLT (IFLT) leads to a differentiation of the effect of clay concentration on hydraulic conductivity, but it is not suitable enough to estimate the hydraulic conductivity value as the RWP. Direct test comparisons between RWP and IFLT show hydraulic conductivity values of the same order of magnitude. Sample compaction is known to reduce the void ratio variation. However, thickness variation may occur during testing due to a combination of swelling and consolidation effects caused by the hydraulic head. Then, the mechanical behaviour of the compacted sample was investigated with an oedometer. The IFLT method could provide rapid hydraulic performance indication compared to standard permeability tests. Further investigations would be needed to properly take into account the mechanical effect of the pressure.