Hydraulic Conductivity Of Compacted Clay Research Articles

Assessment of frost and heating penetration in compacted clay layers of landfill top covers in temperate climate

Compacted clay (CC) layers are commonly used as hydraulic barriers in landfills, thanks to their impervious capacity. However, mechanical and hydraulic properties of CC can be significantly affected by temperature variations due to the heat produced by waste degradation as well as to external air temperature and weathering. Previous experimental tests show that the most detrimental occurrence is the cyclic freezing–thawing (FT) that can increase the hydraulic conductivity of CC up to one order of magnitude. This paper aims at assessing the temperature distribution in a landfill multilayered top cover in several scenarios of temperature solicitations, in order to evaluate the depth of frost penetration. For this purpose, a 2D hydro-thermal coupled finite element model representing a case study landfill top cover has been developed; each constituting layer has been characterized by physical and thermal properties acquired through direct measurements on sampled materials in unfrozen and frozen conditions. The model provides a reliable time description of the isotherm distribution within the layered top cover in several temperature scenarios typical of a temperate climate, thus estimating the penetration of the frost front as well as of high temperatures.

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

Swelling-Pressure and Hydraulic Conductivity of Compacted Clays Focusing on the Clay-Mineral Type

اثر دما بر ضریب نفوذپذیری خاک رسی متراکم و عایق رسی ژئوسینتتیک (GCL)

تاثیر دما در خواص نفوذپذیری خاک‌های رسی متراکم یکی از پارامترهای اساسی در طراحی لایه‌های عایق مهندسی است که در معرض شیرابه‌ها هستند. در این تحقیق اثر دما بر ضریب نفوذپذیری رس متراکم منطقه نازلوی ارومیه و عایق های رسی ژئوسینتتیک و همچنین تاثیر میزان تنش موثر و دانسیته بر نرخ تغییر ضریب نفوذپذیری نمونه های رسی بررسی شده است. دستگاه تعیین ضریب نفوذپذیری سه محوری با دیواره انعطاف پذیر برای اندازه گیری ضریب نفوذپذیری نمونه ها تحت تاثیر دما مورد استفاده قرار گرفته است. با افزایش دما ویسکوزیته محلول کاهش یافته و اثرات دمایی ساختار خاک را تغییر می دهد و تولید حفرات بزرگتر بین ذرات رس می کند و باعث ایجاد تغییر در سطح مقطع موثر جریان شده و آب جذب شده تبدیل به آب آزاد می شود و در نتیجه باعث افزایش ضریب نفذپذیری خاک رسی می شود. افزایش تنش موثر باعث می شود نرخ افزایش در ضریب نفوذپذیری در اثر افزایش دما کاهش یابد. همچنین با افزایش دانسیته خاک رسی، ضریب نفوذپذیری و نرخ افزایش آن کاهش می یابد. بر خلاف خاک‌های رسی، در عایق های رسی ژئوسینتتیک افزایش دما تاثیر چندانی در ضریب نفوذپذیری این لایه ها نداشته و زمانی که این لایه ها در معرض افزایش دما قرار گیرند به عملکرد خوب خود به عنوان یک مانع هیدرولیکی ادامه می‌دهند.

Combined effects of wet-dry cycles and interacting fluid on desiccation cracks and hydraulic conductivity of compacted clay

Compacted clays are used as barriers in landfills mainly due to their low hydraulic conductivity and self healing properties. These clays are subjected to moisture fluctuations and simultaneously exposed to leachates. Besides swelling, the shrinkage and cracks developed during drying get altered due to their exposure to contaminants and control their hydraulic behaviour. Therefore, this paper quantifies the volumetric behaviour and cracks pattern of compacted clay exposed to salt solutions during wet-dry cycles using X-ray computed tomography (XCT) imaging experiments. The results showed that the cracks volume of clay specimen interacted with 4 M NaCl solution is significantly greater than the specimens interacted with distilled water (DW) and 0.4 M NaCl solution at the end of drying cycles. XCT and digital camera imaging experiments showed that the cracks did not develop at same locations in specimen interacted with DW, indicating the self healing property of clay. However, the development of cracks at same locations in specimen interacted with 4 M NaCl solution indicates the complete deterioration of self healing property of clay. This resulted in significantly higher hydraulic conductivity of compacted specimen interacted with 4 M NaCl solution than the specimens interacted with DW and 0.4 M NaCl solution at the end of different wetting cycles.

Deformation and Hydraulic Conductivity of Compacted Clay under Waste Differential Settlement

Landfill is still the most important process to dispose of municipal solid waste in China, while landfill closure aims for pollution control, security control, and better land reuse. However, uneven settlement of landfill cover system is very likely to cause deformation and cracking. The objective of this paper is to examine the effects of geogrid reinforcement on the deformation behaviour and hydraulic conductivity of the bentonite-sand mixtures that are subjected to differential settlement. The laboratory model tests were performed on bentonite-sand mixtures with and without the inclusion of geogrid reinforcement. By maintaining the type and location of the geogrid within the liner systems as constant, the thickness of the bentonite-sand mixtures is varied. The performation of the liner systems with and without the inclusion of geogrid reinforcement was assessed by using jack to control differential settlement. Un-reinforced bentonite-sand mixtures of 100 mm and 200 mm thickness were observed to begin cracking at settlement levels of 2.5 mm and 7 mm, respectively. When settlement reached 25 and 42.5 mm, cracks for 100 mm and 200 mm thick bentonite-sand mixtures without geogrid penetrated completely. The settlement levels for bentonite-sand mixtures of 100 mm thickness with and without geogrid reinforcement was found to be 10 mm and 15 mm, respectively, when its hydraulic conductivity was around 5 * 10−7 cm/s. In comparison, geogrid reinforced bentonite-sand mixtures was found to sustain large deformation with an enhanced imperviousness. The results from the present study can provide theory evidence of predicting deformation and hydraulic conductivity of the landfill cover system.

Pengaruh Kadar Air Dan Enerji Pemadatan Terhadap Hydraulic Conductivity Lempung Yang Dipadatkan

This research will observe the effect of water content and compaction effort to the hydraulic conductivity of Karang Pilang Surabaya Clay used for clay liner of municipal waste disposal area. In this research, clay was taken from Karang Pilang, Surabaya. Clay was compacted with Standard Proctor and Modified Proctor Tests. From each of them,five sample were prepared at different water content (w c apt ),2 (two) at w c <w c apt (wet side). In order to obtain the hydraulic conductivity (k) of the clay liner, falling head test using 0.005 N CaSO 4 was carried out. The result showed that hydraulic conductivity of compacted clays with the increasw of water content until ± 4 % over w opt . The hydraulic conductivity of compacted at wit side is lower than the clay compacted at dry side. The increase of compaction effort increasing density of clay results in the increase of hydraulic condctivity significantly. For different clays, higher density does not assurance lower hydraulic conductivity, the hydraulic conductivity is also influenced by plasticity of clays.

Long-term hydraulic conductivity of compacted clay permeated with landfill leachates

Long-term hydraulic conductivity of compacted clay permeated with landfill leachates

Effects of leachate infiltration and desiccation cracks on hydraulic conductivity of compacted clay

Both cracks in clay liner and the complex composition of landfill leachate might have effects on the hydraulic conductivity of a compacted clay liner. In this study, the hydraulic conductivities of natural clay and bentonite-modified clay with and without desiccation cracks were measured, respectively, using three types of liquids as permeating liquid: 2500 mg/L acetic acid solution, 0.5 mol/L CaCl2 solution, and tap water. When tap water was adopted as the permeating liquid, desiccation cracks resulted in increases in the average value of hydraulic conductivity: a 25-fold increase for the natural clay and a 5.7-fold increase for the bentonite-modified clay. It was also found out that the strong self-healing capability of bentonite helped to reduce the adverse impact of cracks on hydraulic performance. In contrast to tap water, simulated leachates (acetic acid and CaCl2 solutions) show no adverse effect on the hydraulic conductivities of natural and bentonite-modified clays. It is concluded that desiccation cracks and bentonite have more significant effects on hydraulic performance than simulated leachates.

Heat Transport and Water Permeability during Cracking of the Landfill Compacted Clay Cover

The heat-moisture transport through the compacted clay was observed in laboratory. The hydraulic conductivity of cracked clay under wetting-drying cycles was also investigated. At the early phase of heating, the temperature of soil columns rose fast and moisture decreased dramatically; after this phase, the temperature rose at a lower speed and moisture loss stabilized gradually. The moisture content of compacted clay at 25 cm depth decayed to 0. The crack intensity factor (CIF) of compacted clay was 0.043 and 0.097; the crack depth was about 6.5 cm and 8.2 cm at 50°C and 60°C, respectively. The hydraulic conductivity of compacted clay was within 8.3 × 10−7to 1.5 × 10−5 cm/s after four wetting-drying cycles. This value was 2~3 orders of magnitude higher than that of uncracked clay.

Influence of leachate pollution on mechanical properties of compacted clay: A case study on behaviors and mechanisms

The environmental safety and engineering stability of landfills are always a concern of the public in view of its potential impact on public health. This study investigates the effect of leachate corrosion on the mechanical properties of a compacted clay. Batch tests were conducted to measure the permeability as well as the compressibility and the shear strength of the compacted clay that was polluted by landfill leachate under different concentrations. The influence mechanisms of leachate on the mechanical properties of compacted clay were investigated through microscopic experiments. The results showed that the hydraulic conductivity of compacted clay decreased because of the reduction in effective porosity resulting from the infiltration of leachate. Moreover, hydraulic conductivity decreased with the increase in leachate concentration and penetration time. The increase in leachate concentration respectively led to a decrease in the cohesion (C) and an increase in the internal friction angle (φ) of leachate-polluted compacted clay. The content of quartz and clay minerals in compacted clay decreased while albite increased after pollution. The compressibility of the compacted clay rises with pollution. An increase in compressibility and compressive deformation as well as a reduction in the compression modulus occurred as the leachate concentration increased. The maximum decline of void ratio was 9.7%.

Influence of Fly Ash on Clay Liner

Compacted clay is commonly used as an essential material for reducing the permeability in landfill sites. However, compacted clay has defect with shrinkage and desiccation cracking during cyclic drying and wetting, which may increase hydraulic conductivity of compacted clay. It’s necessary to modify clay, and make it have anti-cracking performance. The main objective of the study is to determine the content of fly ash on clay. Laboratory tests were done to determine optimum moisture content, hydraulic conductivity, volume shrinkage on different content fly ash modified clay. It was determined that a certain proportion of fly ash can improve the permeability of clay, and reduce the cracking clay.

Effects of solutes on clay–water interactions: Some comments

Schmitz [Schmitz, R.M., 2006. Can the diffuse double layer theory describe changes in the hydraulic conductivity of compacted clays? Geotechnical and Geological Engineering, 24, 1835–1844.] suggests that ‘unique interpretations and predictions of changes in hydraulic conductivity in clays’ follow appropriate interpretation of changes in double layer thickness. Existing data, however, suggest that reality is more complicated and that both the water content-water potential and hydraulic conductivity functions of clay–water systems must continue to be regarded as macroscopically measurable material properties and that double layer considerations provide only qualitative indications of general behaviour. At the same time, the composition of the equilibrium solution remains a necessary characteristic of the hydrostatic and dynamic properties of clay–water systems. Some experiments that might help our understanding of the hydrostatics and hydrodynamics of these systems are suggested.

Can the diffuse double layer theory describe changes in hydraulic conductivity of compacted clays?

Observations related to modifications of the hydraulic conductivity of compacted soils as a consequence of intentional compositional variation of the percolating fluid are often attributed vaguely to calculated changes in double layer thickness. The same calculated decrease or increase in double layer thickness is interpreted differently, depending on which (unconsciously held) boundary conditions authors take into account. The interpretations of different authors seem to be paradoxical only if the boundary conditions have not been mentioned. On the basis of a literature survey and own previously published test results the different boundary conditions have been grouped and divided into classes. With this division the interpretation of changes in double layer thickness will lead to unique interpretations and predictions of changes in hydraulic conductivity.

The log-normal distribution for hydraulic conductivity of compacted clays: Two or three parameters?

Risk and uncertainty assessments for waste containment systems employing clay barriers often include spatial variability in the hydraulic conductivity as part of the analysis. The two-parameter log-normal distribution is often used to describe the spatial variability, but for compacted clays the three-parameter form can be more appropriate. A statistical hypothesis test was developed that can be used to determine if the two- or three-parameter form of the log-normal distribution is more appropriate. The test is based on a likelihood ratio, comparing likelihood functions for the two- and three-parameter forms at their maximums. Likelihood functions are used assuming that a data set can be segregated into a set of distinct groups of hydraulic conductivities. A step-by-step calculation procedure is described and the test is applied to data collected from 45 sites.

Foundry Green Sands as Hydraulic Barriers: Laboratory Study

A laboratory testing program was conducted to assess the use of foundry sands from gray iron foundries, typically called green sands, as hydraulic barrier materials. Foundry green sands are mixtures of fine uniform sand, bentonite, and other additives. Specimens of foundry sand were compacted in the laboratory at a variety of water contents and compactive efforts and then permeated in rigid-wall and flexible-wall permeameters to define relationships between hydraulic conductivity, compaction water content, and dry unit weight. Additional tests were conducted to assess how hydraulic conductivity of compacted foundry sand is affected by environmental stresses such as desiccation, freeze-thaw, and chemical permeation. Results of the tests show that the hydraulic conductivity of foundry sand is sensitive to the same variables that affect hydraulic conductivity of compacted clays (i.e., compaction water content, and compactive effort). However, hydraulic conductivities <10−7 cm/s can be obtained for many foundry sands using a broad range of water contents and compactive efforts, including water contents dry of optimum and at lower compactive effort. The hydraulic conductivity of foundry sand was generally unaffected by freeze-thaw, desiccation, or permeation with 0.1 N salt solution or municipal solid waste leachate, but was incompatible with acetic acid (pH = 3.5). Hydraulic conductivity of foundry sands correlates well with bentonite content and liquid limit, with hydraulic conductivity less than 10−7 cm/s being achieved for bentonite content ≥6% and/or liquid limit >20.

Bottom ash from sludge cake as a barrier material to pollutant migration in landfills

Treated urban sewage sludge, which had been dewatered and dried in an open bed, was locally burnt in an open drum and bottom ashes were formed. This work investigated whether these bottom ashes of dried sludge cakes (SCbash)' produced by local labour and equipment, could be used as landfill covers or liners, a function normally served by clay. Laboratory tests were performed to determine the particle size distribution, Atterberg limits, compaction characteristics, hydraulic conductivity and shear strength parameters of the sludge cake. The effects of desiccation and freeze-thaw processes on the hydraulic conductivity of SCbash were also examined. It was found that properly compacted and stabilized SCbash has the requisite properties for use as landfill covers or liners. The SCbash can be compacted into a dense mass with a low hydraulic conductivity of the order of 1.15 X 10 -7 m s-1 (as a comparison, the hydraulic conductivity of compacted clay is around 10-9 m s-1). The compacted SCbash also showed good ...

Bottom ash from sludge cake as a barrier material to pollutant migration in landfills

Treated urban sewage sludge, which had been dewatered and dried in an open bed, was locally burnt in an open drum and bottom ashes were formed. This work investigated whether these bottom ashes of dried sludge cakes (SCbash)' produced by local labour and equipment, could be used as landfill covers or liners, a function normally served by clay. Laboratory tests were performed to determine the particle size distribution, Atterberg limits, compaction characteristics, hydraulic conductivity and shear strength parameters of the sludge cake. The effects of desiccation and freeze-thaw processes on the hydraulic conductivity of SCbash were also examined. It was found that properly compacted and stabilized SCbash has the requisite properties for use as landfill covers or liners. The SCbash can be compacted into a dense mass with a low hydraulic conductivity of the order of 1.15 X 10 -7 m s-1 (as a comparison, the hydraulic conductivity of compacted clay is around 10-9 m s-1). The compacted SCbash also showed good defence against the increases in hydraulic conductivity caused by desiccation and freeze-thaw processes compared with the data reported for compacted clays. The compacted SCbash also has a greater shear strength than is typically expected of compacted clay and therefore is likely to remain stable on a typical landfill slope design based on the shear strength of clay.

Discussion of “Estimating Field Hydraulic Conductivity of Compacted Clay” by John M. Trast and Craig H. Benson

Discussion of “Estimating Field Hydraulic Conductivity of Compacted Clay” by John M. Trast and Craig H. Benson

Closure to “Estimating Field Hydraulic Conductivity of Compacted Clay” by John M. Trast and Craig H. Benson

Closure to “Estimating Field Hydraulic Conductivity of Compacted Clay” by John M. Trast and Craig H. Benson