Flexible Wall Permeameter Research Articles

A Leaching Test for Low-Strength Pervious Shaped Materials Containing Zinc Ashes or Lead Slag

Leaching is a universal process by which contaminants are released from a solid material into the water phase when exposed to water. To test a low-strength pervious monolithic material, we propose a leaching test which is performed by means of a flexible wall permeameter, commonly used to measure the hydraulic conductivity of materials. This technique allows to work according to the principles of a column leaching test and measures the mass transfer driven leaching of contaminants without the need to crush the material. Hence, the field conditions in which the material is applied are better simulated. In this work, two types of stabilised mineral waste materials are tested, namely zinc ashes and lead slag. The cumulative emission at a liquid/solid ratio of 10 (L/S = 10) was for many of the investigated contaminants higher in the column leaching test than in the permeability leaching test. It is believed that the enhanced leachability is caused by the crushing of the material as a pre-condition for the application of column tests which increases first flush effects and augments the pH of the studied materials during leaching. Our results indicate that the column leaching test can overestimate the leachability of certain contaminants with several orders of magnitude. Therefore, we advise to use the permeability leaching test to assess the potential environmental risks associated with e.g. stabilised zinc ashes in a specific application. Thus, this new test gives a more realistic estimate of the field condition leaching of low-strength pervious materials and hence increases the relevance of such an assessment.

점토 함유량에 따른 점토질 모래의 투수 및 압밀 특성 평가

Evaluation of permeability and coefficient of consolidation of clayey sand is critical in analyzing ground stability or environmental problems such as prediction of pollutant transport in groundwater. In this study, permeability tests using a flexible wall permeameter are performed to derive the coefficient of consolidation and permeability of reconstituted soil samples with various mixing ratios of kaolin clays and two different types of sands, which are Jumunjin and Ottawa sands. The test results indicate that the coefficient of consolidation and permeability plots linearly against clay contents in semi-log scale graphs for low clay mixing ratios ranging between 10 to 30%. It is also demonstrated that coefficient of consolidation and permeability of sand and clay mixture are dependent on the soil structure. Contrary to previous findings, the permeability is shown to be independent of the void ratio at low mixing ratios, which can be classified as non-floating fabric. The permeability decreases with the void ratio for floating fabric.

Flexible Wall Permeameter to Measure the Hydraulic Conductivity of Soils in Horizontal Direction

Abstract The flexible wall permeability apparatus was modified for the direct measurement of the hydraulic conductivity of soils in the horizontal direction. Constant head permeability tests were carried out using the radial flow flexible wall permeameter on soil samples with central sand drain to allow the water to flow radially from the central sand drain towards a peripheral drain. Tests were also conducted using the conventional flexible wall permeameter on samples that were trimmed horizontally, so as to measure the hydraulic conductivity in the horizontal directions for comparison. The test results obtained from the proposed setup agrees well with those obtained from the samples that were trimmed horizontally, proving the validity of the results obtained from the proposed apparatus.

Effect of fines content and void ratio on the saturated hydraulic conductivity and undrained shear strength of sand–silt mixtures

The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.

Long term leachate evolution during flow-through leaching of a vault backfill (NRVB)

AbstractSome of the illustrative concepts for the disposal of intermediate-level waste in a geological disposal facility in the UK employ a cementitious backfill around the waste packages. The concept for higher strength rocks would use a highly alkaline backfill composed of Portland cement (now known as CEM I), hydrated lime and limestone flour, referred to as Nirex reference vault backfill (NRVB).This paper reports a study of the extensive leaching of cured NRVB in a range of generic leachant compositions (deionized water, 0.1 M and 1 M NaCl solutions) under flow-through conditions using a flexible wall permeameter. The experiments were designed to run for up to two years and to pass at least 1000 volumes of leachant (defined as the cumulative leachate volume produced/NRVB solid specimen volume) through the NRVB samples. Results for the pH evolution profiles of the leachates and the microstructural analysis of the unleached and leached samples are presented.

On measuring the hydraulic transmissivity of the geotextile cover of geosynthetic clay liners

ABSTRACT: This paper presents a new approach to the utilisation of a flexible-wall permeameter to measure the hydraulic transmissivity of a geotextile. The proposed method is simple, and requires neither additional equipment nor a special test procedure. To highlight the features of the proposed test method, the results of tests conducted on the cover geotextile specimen of a geosynthetic clay liner under different confining pressures are presented and discussed. This study was a part of larger project investigating leakage rates through composite liners comprising a geomembrane containing defects overlying a geosynthetic clay liner.

Predicting the saturated hydraulic conductivity of soils: a review

This paper examines and assesses predictive methods for the saturated hydraulic conductivity of soils. The soil definition is that of engineering. It is not that of soil science and agriculture, which corresponds to “top soil” in engineering. Most predictive methods were calibrated using laboratory permeability tests performed on either disturbed or intact specimens for which the test conditions were either measured or supposed to be known. The quality of predictive equations depends highly on the test quality. Without examining all the quality issues, the paper explains the 14 most important mistakes for tests in rigid-wall or flexible-wall permeameters. Then, it briefly presents 45 predictive methods, and in detail, those with some potential, such as the Kozeny-Carman equation. Afterwards, the data of hundreds of excellent quality tests, with none of the 14 mistakes, are used to assess the predictive methods with a potential. The relative performance of those methods is evaluated and presented in graphs. Three methods are found to work fairly well for non-plastic soils, two for plastic soils without fissures, and one for compacted plastic soils used for liners and covers. The paper discusses the effects of temperature and intrinsic anisotropy within the specimen, but not larger scale anisotropy within aquifers and aquitards.

SRSL 매립지 최종 복토층의 투수 및 강도 특성

본 연구는 매립지의 최종복토층으로 사용되는 점토 혹은 지오멤브레인의 부등침하 및 기상조건변화에 의한 균열에 취약한 점을 고려하여 균열 발생시 자가형성된 물질로 인하여 균열치유 작용을 할 수 있는 SRSL(Self Recovering Sustainable Liner)의 매립지 최종복토층으로서의 적용성을 파악하였다. SRSL 기법은 2개의 층을 두어 상, 하부층 사이 계면에 불투수성 물질을 생성하는 동시에, 균열발생 시에도 2가지 성분이 다시 결합하여 불투수성 물질을 재형성하는 역할을 수행한다. SRSL의 최종복토층의로서의 적용성 파악을 위해서 실험실에서 연성벽체 투수시험기를 사용하여 투수 특성을 파악하였고 일축압축시험을 통하여 강도 및 강성 특성을 파악하였다. 또한 최종 복토층의 경우 환경적인 요인에 직접적으로 노출되어 있기 때문에 동결/융해 및 건조/습윤에 따른 SRSL의 투수 및 강도 특성 또한 알아보았다. 시험 결과, SRSL은 낮은 투수계수와 기준보다 높은 강도를 가진 매립장의 복토층 재료로 적합한 물질로 판단되며, 동결/융해 및 건조/습윤의 환경적인 영향에 대해서도 안정한 것으로 판명되었다. Conventional designs of landfill covers use geosynthetics such as geomembrane and GCL, and clay liners to lower the permeability of final covers of landfill sites. However, differential settlement and the variation of temperature or humidity in landfill sites cause the development of cracks or structural damage inside the final cover. This study examined the application of a Self Recovering Sustainable Liner (SRSL) as an alternative landfill final cover material. SRSL consists of double layers, which have chemicals, can generate precipitates filling the pores of the layers by chemical reaction. The interface material forms an impermeable layer and in case of internal cracks, the reactants of the two layers migrate towards the crack and heal it by forming another liner. In this study the applicability of SRSL material for landfill final cover was examined by performing flexible wall permeameter tests to prove that the hydraulic conductivity is lower than the regulations and unconfined compression tests to judge whether the strength satisfies the restriction for the landfill final cover. Furthermore, the environmental impacts on the permeability and strength were evaluated. The experimental results show that the SRSL has lower hydraulic conductivity and higher strength than the regulations and is little influenced by climatic changes such as wet/dry or freeze/thaw process.

Retartation Performance to Pollutants of Antiseepage Slurry for Waste Landfill Sites

Based on self-developed bentonite - fly ash - cement（BFC）slurry and flexible wall permeameter, infiltration test was conducted on slurry concretion samples of different height using heavy metal ions Solution and leachate from waste landfill site. Test proved that as a result of the infiltration deposition and adsorption residence performance, retardation by slurry concretion happened in about 30mm of initial infiltration to 95% of heavy metal ion pollutants(Hg, As, Pb, Cr, Cd etc.) and 60% of waste leachate pollutants (NH4-N, TN, TP, CODCr, BOD5 etc.). Moreover, blocking rate for all pollutants presents an increasing trend along with the increase of the height of slurry concretion samples in a defined way.

A Flexible Wall Permeameter for the Determination of the Water Permeability Function in Unsaturated Soils

Abstract This paper describes the development of a suction controlled flexible wall permeameter for the direct determination of the water permeability function in unsaturated soils. The new permeameter works with applied constant head or constant rate of flow, i.e., the common steady-state techniques. Total volume change of soil specimens during the test are monitored using a high resolution electronic scale. Numerical simulations were performed to evaluate the influence of factors such as flow velocity and matric suction distribution within the specimen and effects of sample height on such factors. Analyses of tests conducted on two tropical soil samples are used to evaluate conventional proposals for the determination of the water permeability function. It is shown that such proposals do not apply in the case of the materials tested and solutions to that are put forwards.

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.

Study on the Permeability of Reinforced Soil with Herb Fiber under Different Salt Solution Concentration

The best is to read these instructions and follow the outline of this text. n this investigation, laboratory permeability tests were conducted on the wet-processing reinforcement specimens to study the feasibility of reinforced soil as a material of construction. Two kinds of reinforced specimens with different reinforcement materials (wheat straw (C) and flax (M)) were mixed with 3% contents of soil mass, and product to the cylindroid for measurement of permeability by a flexible-wall permeameter. The variation relationship between permeability coefficient and Na2SO4 concentrations was analyzed. Test results show that the liquidity reduced with incrassate diffusion layer caused by the increasing Na+ concentrations in the diffusion layer of soil particles, and then a decrease of permeability is found. With the increasing time of permeability, it is found that the permeability coefficient decreased due to the consolidation and decreasing porosity of specimens caused by the change of stress state. At the same time, ion exchange adsorption and water film incrassate occurs in soil particle surface which also benefit to the decrease of permeability coefficient.

Applicability of cement-based grout for ground heat exchanger considering heating-cooling cycles

The applicability of cement grout (or cement-based grout) has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between −5°C and 50°C. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35°C. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.

Consolidation and Hydraulic Conductivity of Zeolite-Amended Soil-Bentonite Backfills

The effect of zeolite amendment for enhanced sorption capacity on the consolidation behavior and hydraulic conductivity, k, of a representative soil-bentonite (SB) backfill for vertical cutoff walls was evaluated via laboratory testing. The consolidation behavior and k of test specimens containing fine sand, 5.8% (dry weight) sodium bentonite, and 0, 2, 5, or 10% (dry weight) of one of three types of zeolite (clinoptilolite, chabazite-lower bed, or chabazite-upper bed) were measured using fixed-ring oedometers, and k also was measured on separate specimens using a flexible-wall permeameter. The results indicated that addition of a zeolite had little impact on either the consolidation behavior or the k of the backfill, regardless of the amount or type of zeolite. For example, the compression index, Cc, for the unamended backfill specimen was 0.24, whereas values of Cc for the zeolite-amended specimens were in the range 0.19≤Cc≤0.23. Similarly, the k for the unamended specimen based on flexible-wall tests was 2.4×10-10 m/s, whereas values of k for zeolite-amended specimens were in the range 1.2×10-10≤k≤3.9×10-10 m/s. The results of the study suggest that enhancing the sorption capacity of typical SB backfills via zeolite amendment is not likely to have a significant effect on the consolidation behavior or k of the backfill, provided that the amount of zeolite added is small (≤10%).

Engineering Properties of Fibrous Paper Mill Sludge from Southern Brazil

The paper recycling process generates a sludge characterized by a high content of cellulose fiber. To understand the behavior of this fibrous material, this article presents an interpretation of the geotechnical behavior of a waste sludge from a paper recycling plant situated in southern Brazil using data from laboratory tests. Engineering properties of compacted paper mill sludges are similar to those of most fibrous organic soils: low hydraulic conductivity upon compression and high compressibility. The waste studied has a water content of approximately 250%, organic content of 48%, mineral charges, and water. The one-dimensional compressibility parameters are indicative of high compressibility. For the determination of the strength parameters of the material, undrained triaxial tests were carried out. An incredibly high effective friction angle (ϕ′=53°) was found, probably because of the fibrous nature of the paper sludge. In addition, hydraulic conductivity tests were performed on a flexible wall permeameter. The hydraulic conductivity of the fibrous paper sludge reached values near10-9 m/s. The results showed that the paper mill sludge is a ductile material with reduced hydraulic conductivity and elevated shear strength that could have multiple applications, such as in the construction of bottom liners, cover liners, and steep side-slope liners for solid-waste landfills.

Study on the Hydraulic Conductivity of Sand-Bentonite mixtures used as Liner System of Waste Landfill

A liner system such as liner sheet underlying impermeable soil layer having hydraulic conductivity less than 1*10-7 cm/s and a thickness larger than 100 cm is often used in china. As there is very little natural clay having such low permeability, bentonite is usually mixed into sand to decrease the permeability. In this paper, the compaction tests and permeability testing using flexible-wall permeameter are conducted. The test results show that the value of critical benonite ratio depends on bentonite ratio, and the hydraulic conductivity of the sand mixed with critical bentonite ratio for distilled water shows of the order of 1*10-8 cm/s that satisfies the china standard requested as compacted soil liner of waste landfill. Finally, the permeability testing used leachate including calcium component was conducted.

Hydraulic Properties of Asphalt Concrete

Abstract This paper presents the laboratory results and methods used to measure the hydraulic parameters of asphalt concrete core samples. The same testing methods used to measure the saturated hydraulic conductivity and moisture retention in soils were applied to the asphalt concrete cores. Moisture retention was analyzed according to the van Genuchten (1980) mathematical model to produce the drying portion of the moisture retention curves. In addition to standard desorption tests, wetting curves were developed for two asphalt concrete cores. Saturated hydraulic conductivity was measured using a flexible wall permeameter. The asphalt concrete differs from these soils by maintaining a much lower porosity, and the dry asphalt concrete exhibited a water repellant behavior.

Testing system for hydraulic properties of unsaturated nonwoven geotextiles

ABSTRACT: The water retention curve (WRC) of unsaturated nonwoven geotextiles is necessary for the prediction of transient water flow in unsaturated soil–geotextile systems. A test method is introduced in this study to measure the WRC of deformable, unsaturated nonwoven geotextiles. This test method combines the axis-translation technique with water flow control using a flow pump. Specifically, a nonwoven geotextile specimen is placed within a flexible wall permeameter atop a cellulose membrane having high air entry and low impedance, and the flow pump is used to impose upward or downward water flow across the membrane. A control loop is used to reach stable suction values at the boundary of the suction in order to ensure that points on the WRC are defined for equilibrium flow conditions. A piston is used to apply a vertical load on the nonwoven geotextile specimen in order to replicate field loading conditions, and was also useful for measurement of changes in specimen volume. The combination of flow control, suction stabilization, and height measurement allow this new approach to effectively consider the impact of normal stress and matric suction on the porosity of the geotextile during measurement of the WRC. Experimental results for typical tests indicate that this approach yields drying and rewetting WRC curves for a geotextile specimen consistent with those in the technical literature.

Hydraulic Conductivity and Shear Strength Behavior of Compacted Lateritic Soil-Bentonite Mixtures Used for Sanitary Landfill Liners

The use of soil-bentonite mixtures for sanitary landfill liners with the purpose of retaining pollutants is becoming very common. This work shows the results of hydraulic conductivity and shear strength tests performed with soil-bentonite mixtures with bentonite contents of 3%, 5% and 7%. Additionally, shear strength test results carried out with a mixture with bentonite content of 9%, are shown. The selected natural soil for this research is a lateritic residual clayey sand originated from Adamantina Formation sandstones of the Bauru Group. Samples of this soil were collected in the Pindorama County, which is located in the northeast of the State of Sao Paulo, Brazil. The hydraulic conductivity tests were performed with rigid and flexible wall permeameters. Test results show that mixtures with bentonite content higher than 6% are suitable, in terms of hydraulic conductivity, for the construction of sanitary landfill liners. The shear strength parameters of natural soil and mixtures were assessed by performing undrained triaxial compression tests and unconfined compression tests. It was found that there is a tendency showing that the cohesion increases when the bentonite content is increased. The addition of bentonite to natural soil causes the friction angle to decrease. However, it cannot be concluded from test results, that the higher the bentonite content, the lower the friction angle. In terms of shear strength, the unconfined compression test results have shown that mixtures with bentonite content of 5% are suitable for the construction of sanitary landfill liners when relative compaction is equal or higher than 95%.

Measurement of filtration effects on the transmissivity of geocomposite drains for phosphogypsum

Geocomposite curtain drains are commonly used in phosphogypsum waste stacks to mitigate stability concerns. Specifically, they are used to lower the piezometric surface in the phosphogypsum by diverting water flow near the toe of the stack slopes. Phosphogypsum has high fines content, low plasticity, and slight solubility, all of which are indicators that its filtration behavior should be evaluated in addition to using filtration criteria developed for soils. The objective of this study is to investigate the impact of filtration on the in-plane flow capacity of geocomposites used as a curtain drain in problematic soils like phosphogypsum. Specifically, a flexible-wall permeameter was adapted with a bottom platen that permits both a gradient ratio filtration test and an in-plane transmissivity test to be performed on a soil–geocomposite system. Measured gradient ratio values for compacted phosphogypsum underlain by a geocomposite with 200 g/m 2 nonwoven geotextiles ranged from 0.94 to 0.63 for cross-plane target gradients ranging from 0.7 to 24.9. Although these gradient ratio values indicate a possibility for some particle loss across the filter via piping, especially under high target gradients, steady seepage conditions were obtained. However, the transmissivity measured after each filtration test was not observed to change significantly, indicating that the geocomposite was suitable for use as a curtain drain in phosphogypsum. The dual-purpose experimental approach developed in this study was found to provide complementary information to existing filtration criteria when using geocomposites in potentially problematic soils.