Thick Liner Research Articles

Test field study of different cover sealing systems for industrial dumps and polluted sites

Six test fields (3×15 m) with an inclination of 5% have been set up on a landfill for blast furnace dust. A 75-cm thick covering layer (recultivating layer) had been the same for all test fields. The efficiency of different sealing layers (clay liner, geosynthetic clay liner, capillary barrier and the blast furnace dust itself) had been investigated for more than 2 years. The objective of this study was to obtain, under natural conditions, data on the water regimen and the motion of the water in surface sealing systems and to perform a comparative evaluation regarding effectiveness and economic efficiency. It could be shown that a kind of capillary barrier effect above an underlying drainage layer can be obtained by an adequate choice of soils with a high field capacity and thus inducing an important runoff in the recultivating layer. The geosynthetic clay liner and the 30-cm thick clay liner with an overlying drainage were the only systems to meet the permeability requirements ( k value<5×10 −9 m/s) of the German regulatory standards. The geosynthetic clay liner showed a slight increase in permeability in the second year due to cation exchange processes, whereas a clay liner without overlying drainage failed totally because of a distinct desiccation behaviour.

Atomistic simulations of deep submicron interconnect metallization

Damascene approaches are widely used for creating microelectronic interconnects. Successful implementation of the process is reliant upon the deposition of a refractory metal or metal nitride liner coating. It functions as a diffusion barrier layer to suppress transport of subsequently deposited interconnect metals into the surrounding dielectric. The development of vapor-phase processes for the deposition of uniform thickness liner layers has been problematic. Flux collimation and energetic deposition approaches have been attempted with mixed results as the feature size is decreased. Here, a modified kinetic Monte Carlo (KMC) method has been used to explore the physical vapor deposition of liner coatings. To incorporate the many effects associated with energetic metal fluxes, the results of molecular dynamics calculations of incident atom reflection, resputtering, surface biased diffusion, and athermal relaxations have been introduced into the KMC algorithm. The method has been applied to investigate the effects of the incidence flux’s angular distribution and kinetic energy upon the liner coating coverage. It has been found that trench step coverage uniformity increases with increasing atom kinetic energy above a threshold energy value of 20 eV. Atom resputtering/reflection are found to be the most important mechanisms responsible for improvements in the step coverage. Sputtering of already deposited material is found to be the most important mechanism for transporting the flux to the most difficult to coat lower sidewall region of a trench. Energetic deposition processes that activate these mechanisms are therefore preferred. The simulations reveal the existence of an optimal incident angular distribution to maximize coverage uniformity. For a flux with a kinetic energy of 70 eV, a cosine angular distribution within the collimation angle of ±15°–25° provided the best balance of direct and resputtered/reflected fluxes to maximize coating uniformity.

Inelastic stability of tightly fitted cylindrical liners subjected to external uniform pressure

The critical external pressure at which a thin cylindrical liner may buckle elastically has gained many researchers' attention. In contrast, the inelastic buckling pressure of thick cylindrical liners has never been examined thoroughly. A previous attempt was reported by Jacobsen who had limited the critical external pressure to the value that coincided with the onset of yielding of the most heavily stressed part of the cylindrical liner. The liner thickness-to-diameter and yield stress-to-Young's modulus ratios, both control the ultimate capacity of any liner. This paper presents a parametric study using the Finite Element Method (FEM), evaluates Jacobsen solution and provides charts that help in estimating the ultimate pressure capacity of such cylindrical liners.

Predicting Leakage through Composite Landfill Liners

Leakage through composite landfill liners having various characteristics was analyzed using existing analytical and numerical models developed for the study. Three-dimensional numerical models were used to analyze leakage through circular defects and two-dimensional numerical models were used to analyze leakage from defective seams. Leakage rates predicted with the numerical models were compared to leakage rates predicted using existing equations and analytical models currently being used. These comparisons show that existing equations and analytical models all have limitations and no universal equation or method is available for predicting leakage rates. To overcome some of the deficiencies in the existing equations and models, new equations were developed based on results from the numerical models. Recommendations are made for using the new equations, existing equations, and analytical models to predict leakage rates in thick composite liners having a geomembrane overlaying a compacted soil liner and thin composite liners having a geomembrane overlaying a geosynthetic clay liner.

CVD and PVD copper integration for dual damascene metallization in a 0.18 μm process

Various methods of copper filling are studied as interconnect metallizations in advanced ultra large scale integration (ULSI) devices. The filling mode comprising organometallic chemical vapor deposition (OMCVD) Cu followed by physical vapor deposition (PVD) Cu reflow for 0.3 μm diameter trench and via filling has been investigated. This paper presents an evaluation of both the long-throw PVD copper, and CVD copper fundamental process steps. The excellent step coverage of CVD Cu as a seed layer is presented. The corresponding initial PVD Cu deposition step requires a low DC power to facilitate Cu reflow before creating the characteristic overhang of the PVD process, which in turn facilitates subsequent void formation. So the PVD DC power was optimised at 1.6 kW. Furthermore, the full sequential integration of the CVD and PVD process was investigated as a function of liner thickness, deposition temperature and DC power. The filling process has been optimised with a relatively thick liner, to avoid dewetting on the TaN barrier, and with a high deposition temperature to obtain sufficient reflow. However, a thin PVD Cu ‘flash’ layer was necessary to resolve interface stability issues between CVD Cu and TaN. Electrical results are compared to those from a standard copper process flow and these first results are 15% higher than with a standard copper metallization.

Mechanisms for very long electromigration lifetime in dual-damascene Cu interconnections

Electromigration in 0.27 μm wide Cu damascene interconnections has been investigated. The results show that the electromigration time to failure of Cu interconnections is greatly influenced by the thickness of the metal liner at the contact between the via and underlying line. A remarkably long lifetime was achieved when a 3 nm thick liner (at the via/metal line interface) was used, since the abrupt mass flux divergence at this interface normally seen is greatly diminished. Voids were found in the regions where there was no electric field and on the bamboo Cu grain structure. Void formation is explained by the effect of a vacancy wind.

A mobile shield to reduce scatter radiation to the contralateral breast during radiotherapy for breast cancer: preclinical results

Purpose: To design a practical breast shield and to investigate its efficacy in reducing scattered radiation to the contralateral breast of patients undergoing radiation therapy for breast cancer.Methods and Materials: We constructed a mobile shield consisting of (a) a mobile base and a counterweight; (b) a vertical column adjustable in height and a diagonal arm adjustable in angle; (c) a curved, 2.5-cm thick lead sheet with a 1-cm thick polystyrene liner for blocking scattered radiation; and (d) diode detectors to verify that the edge of the lead sheet is not in the useful beam in addition to the use of the field light. Measurements were performed with thermoluminescent dosimeters on 10 patients without the shield and on an anthropomorphic phantom with a pair of wax breasts with and without the shield. All of the patients were treated with 6-MV photons (Varian 6/100). The scattered radiation from the medial and lateral fields was measured separately.Results: The contribution of the medial field to the total scattered dose was 70% to 75%, whether a medial wedge was used or not. However, without a medial wedge, the scattered dose was reduced by nearly 33% at 3 to 9 cm away from the medial border. In the anthropomorphic phantom study with wax breast, the mobile shield reduced the medial field contribution to the total scatter dose to less than the contribution from the lateral field without a shield. With a prescribed dose of 50 Gy and a medial wedge, the median scatter dose to the contralateral breast from 6 patients was 5.3 Gy; without a medial wedge, it was 3.8 Gy from 4 patients at 6 cm from the medial border. In the phantom study, with the shield the total dose to the contralateral breast was 1.0 Gy at 6 cm from the medial border with a same prescribed dose.Conclusion: The mobile shield reduced the scatter dose to the contralateral breast from the linear accelerator (Varian 6/100, 6-MV photons) by a factor of 3 to 4. The shield greatly reduced the scattered dose in the wax phantom. Equivalent reductions in patients may be clinically significant by reducing the risk of radiation-induced breast cancer in the contralateral breast of woman undergoing radiation therapy for breast cancer. The shield is safe and easy to adjust to each patient.

Gothenburg Osseointegrated Hip Arthroplasty

The culmination of more than 10 years of laboratory and clinical research has been the clinical trial of a novel hip arthroplasty for osseointegration. The femoral component of this Gothenburg hip is a neck retaining, threaded fixture with rotational symmetry, produced in commercially pure titanium with a specific surface texture. Proximally, a standard orthopaedic taper trunnion mates with a 28-mm diameter zirconia head that articulates against the acetabular component. The latter is also of textured commercially pure titanium, encapsulating a thick ultra high molecular weight polyethylene liner. Dedicated alignment guides and cutting instruments ensure accurate bone preparation and implant placement. Limited clinical trials commenced in 1992 and expanded to multicenter clinical trials in 1997. Every hip has been monitored with radiostereometry to measure migration to an accuracy of 0.1 mm. All calcar implanted femoral components show excellent function at 4 to 5 years followup, with no migration revealed by radiostereometry.

A comparison of the convective and diffusive flux of organic contaminants through landfill liner systems

In an effort to protect groundwater, waste disposal regulations now require the use of composite liners consisting of com pacted soil overlain with a flexible plastic membrane liner in both hazardous and municipal solid waste landfills in the USA. When properly installed, composite liners decrease the convective flux of leachate flowing through flaws in the plas tic ; however, even if all flaws could be eliminated, organic chemicals will diffuse through the liner system. Although actual field measurements are not available on the flux of contaminants through landfill liners, field measurements of leachate concentrations at some landfills, leak rates at other landfills and laboratory data on diffusion coefficients, allow estimation of the flux so that convective and diffusive trans port can be calculated. Calculations were made to estimate the flux of five organic chemicals through liners of various designs. For the flexible membrane liner alone, the flux of organic chemicals is dominated by diffusion, and transport by convective flux through flaws is one or two orders of magni tude less. For a 100 cm thick clay liner alone, the flux of organic chemicals is dominated by convective flow since the long path length limits diffusive flux. For a composite liner including a flexible membrane over a 100 cm thick clay liner, the flux of organic chemicals is dominated by convective transport since the diffusion path length through the compos ite liner is much greater than that through the flexible mem brane liner (FML) alone. For a typical composite liner in which the FML contains 30 holes/ha -1, the convective flux of organic chemicals is typically two orders of magnitude greater than the diffusive flux. A liner consisting of an FML, or an FML combined with a thin layer of low permeability soil, will allow a much greater flux of contaminants than a composite liner consisting of an FML and a thick layer of low permeabil ity soil.

Finite element analysis of a pilot gas storage in rock cavern under high pressure

A three-dimensional finite element analysis was performed to simulate field tests at a pilot gas storage project. The storage was a shallow rock cavern lined with a 6 mm thick steel liner. During the tests, high internal pressure up to 52 MPa was applied and deformation of both rock mass and the steel liner was recorded. The maximum rock displacements of less than 6 mm was numerically predicted and fits the measurement very well. The three-dimensional nonlinear finite element modeling has confirmed the overall stability of the structure and revealed the functioning of each structural component, including the rock mass, concrete lining and the steel liner.

Performance of Protective Cover Systems for Landfill Geomembrane Liners Under Long-Term MSW Loading

This paper presents the results of large-scale laboratory simulation tests conducted to evaluate the relative performance of different cover systems, consisting of a granular soil layer (i.e. a drainage layer) both with and without the presence of a needle-punched nonwoven geotextile, to protect a 1.5 mm thick smooth HDPE geomembrane liner under long-term municipal solid waste (MSW) loading conditions. Five different granular soils that range from a coarse gravel to a medium sand were used in the testing program. The protective cover system and the geomembrane liner were subjected to incremental loading to a maximum pressure of 1.4 MPa. The effect of long-term loading on the characteristics of the cover soils was assessed by performing particle size analyses, and the physical damage that occurred to the geomembrane liner was visually assessed in addition to performing multi-axial tension, wide strip tension, and water vapor transmission tests. The test results revealed that the degree of geomembrane liner protection decreases as the soil mean particle size increases and as the soil particle sphericity decreases. This study demonstrates that a 300 mm thick granular soil layer consisting of particles with a mean size less than 30 mm and a sphericity greater than 0.8, combined with a 270 g/m2 nonwoven geotextile provides adequate protection for a 1.5 mm thick HDPE geomembrane liner from MSW loading.

Optimization in thickness of a liner composed of claymax® and organo-clay

Present design philosophy reflects the uncertainty about the long-term effectiveness of liner systems by incorporating redundancy in the barrier layers through the concurrent use of both geosynthetic and clay minerals. A possible reason may be the lack of an engineering based design procedure for liners and a lack of a suitable optimization model which can be used to predict liner performance. In this study, Claymax® and Organo-Clay are chosen to be the liner materials because of their low hydraulic conductivity and high sorption capacity, respectively. The simulation model “Pollute 3.3” is combined with the Generalized Reduced Gradient Methods “GRG2” code to form an optimization model. The objective of this optimization model is to provide a tool for engineers to design a liner of reasonable thickness that protects the environment and maximizes disposal space. It was found that the total liner thickness is dependent on the sorption capacities of chemicals, equivalent hydraulic conductivities, and the geometry of a landfill.

Optimization in thickness of a liner composed of claymax® and organo-clay

Present design philosophy reflects the uncertainty about the long-term effectiveness of liner systems by incorporating redundancy in the barrier layers through the concurrent use of both geosynthetic and clay minerals. A possible reason may be the lack of an engineering based design procedure for liners and a lack of a suitable optimization model which can be used to predict liner performance. In this study, Claymax® and Organo-Clay are chosen to be the liner materials because of their low hydraulic conductivity and high sorption capacity, respectively. The simulation model “Pollute 3.3” is combined with the Generalized Reduced Gradient Methods “GRG2” code to form an optimization model. The objective of this optimization model is to provide a tool for engineers to design a liner of reasonable thickness that protects the environment and maximizes disposal space. It was found that the total liner thickness is dependent on the sorption capacities of chemicals, equivalent hydraulic conductivities, and the geometry of a landfill.

Filament-wound pressure vessel with thick metal liner

A method for calculating stress and strain in non-symmetric filament-wound pressure vessels with thick metal liners, up to burst pressure, is presented. The calculations are based on classical laminate theory and Tsai-Wu failure criterion. Plastic yielding of the liner and transverse cracking of the composite are not considered failures of the vessel and are modelled by reduced properties. The effect of changing thicknesses of various layers, on burst pressure and efficiency of the vessel, is considered. It is shown that the efficiency of a thick liner reinforced with filament winding can approach optimal values that are quoted in the literature, even when the liner is selected arbitrarily. The calculations agree with test results of two 6 litre vessels having the same liner: one with Kevlar 49/Epoxy overwrap and the other with T300 Carbon/Epoxy.

Depth variations in hydraulic conductivity within a single lift of compacted clay

Compacted clay liners are commonly used as components of the lower portion of composite double liner systems for hazardous waste containment. Because the overlying leachate collection and removal systems and the FMLs are not perfect leachate still comes into contact with the lower liner and thus makes it critical that the clay liner component be constructed to achieve the lowest possible hydraulic conductivity. This research was conducted to evaluate the effects of clod size on the hydraulic conductivity of compacted soils and the uniformity of conductivity with depth within a lift of compacted soil. Two subsoils, one from the Beaumont series (smectitic) and one from the Kosse series (kaolinitic), were evaluated in the laboratory and then compacted in large fixed wall permeameters using maximum clod sizes of <2.5, <5.0, and <7.5 cm to a compacted lift thickness of 23 cm. Measurements were made of the hydraulic conductivity of the entire lift, the lower two thirds of the lift, and the lower one third of the lift. The results show that the conductivity of the lower one third of the lift can be as great as 8.7 times that measured for the entire lift and indicates that liners need to be constructed using thin lifts to achieve more uniform low conductivity throughout the liner. The data also indicated that under the carefully controlled conditions of this study and with the clod sizes used, the clod size did not have a significant effect on the hydraulic conductivity of the soils tested. Soil bulk density was poorly correlated with hydraulic conductivity and indicates that measuring the bulk density of a compacted soil is an inadequate method for assuring low hydraulic conductivity. Measurements of the time to the first appearance of leachate indicated that 8 to 17 d are required for water to penetrate a 23 cm thick compacted liner with an average conductivity of 1 × 10−7 cm s−1.

Coupling impedance of many holes in a liner within a beam pipe.

The longitudinal and transverse impedance of many holes in a thick-wall liner have been calculated for hole dimensions that are small compared to the wavelength. These are shown to be small compared with the corresponding resistive wall impedances of the liner at the frequency of the lowest transverse coupled-bunch mode. Estimates are made of the effect of the propagation of TEM modes in the coaxial region between the liner and beam pipe, and these can be neglected for a sufficiently thick liner. Estimates are also made of the possible coherent effect of uniformly spaced holes.

Excellox 6 and 7 Irradiated Fuel Transport Flasks

AbstractThe Sellafield nuclear fuels reprocessing plant in Cumbria has been receiving Light Water Reactor (LWR) fuel from European and Japanese power stations since the early 1970s. Virtually all of this has been delivered to Sell afield in flasks of composite design. This design of flask comprises a thick lead liner surrounding the fuel cavity and providing gamma radiation shielding, structural strength being provided by an enclosing steel shell. The composite flask has proved to be safe and efficient in operation but is now meeting the limits of its potential due to the trend towards higher burn up fuel High burnup fuel emits increasing levels of neutron radiation which the composite flask was not designed to accommodate; thus the need for new designs of flasks to carry the fuels of the future. The Excellox 6 and Excellox 7 irradiated fuel transport flasks have been developed over a period of five years. They are of monolithic construction and have been designed to complement existing composite flask ty...

Design of a hydrodynamic leachate containment system

This paper presents the design concept for a case study sanitary landfill on a site that would not normally have been approved owing to the presence of a high water table. In this design, the base of the landfill was intentionally placed below the water table. A massive 2.5 m wide, 2.5 m high cutoff wall and a 0.3 m thick liner with hydraulic conductivities of approximately 5 × 10−10 m/s were constructed of recompacted glacial till to limit both groundwater intrusion into the landfill and leachate migration out of the landfill. In this case study, the landfill base was placed below the water table to (i) provide a relatively inexpensive source of cover material and (ii) use the hydrodynamic gradient from the high water table to help contain the leachate. Finite element modelling of the seepage and contaminant transport, for alternate designs for lined and unlined landfills placed above and below the groundwater table, is shown to confirm a previous, less-sophisticated, estimation that placing a lined landfill below the groundwater table has definite advantages in reducing both leachate seepage and contaminant transport. Key words: landfill, leachate, hydrodynamic containment, liners, compacted earth cutoff walls, seepage and contaminant transport modelling.

Permeability protocol for the compacted clay liner at Metropolitan Toronto's Keele Valley Landfill

The Provisional Certificate of Approval to construct a sanitary landfill for municipal waste in an old gravel pit in the Oak Ridges Moraine north of Toronto, Ontario, required that a 1.2 m thick compacted clay liner with a permeability of less than 10−8 cm/s should be placed beneath any refuse. Preliminary testing indicated that the native tills from the immediate vicinity were marginally capable of providing such a liner, as long as they were carefully selected and compacted at moisture contents just above optimum values. However, it was clear that the variability of material and (or) testing was such that some liner samples could have permeabilities greater than 10−8 cm/s. Additionally, there was concern that the sampling and testing procedures could affect the results. This paper details the trials which were carried out at the beginning of construction to establish acceptable sampling and testing techniques.These were finally determined to consist of carefully obtained Shelby tube samples, the permeability of which was tested at representative pressures in triaxial cells. The paper then presents the statistical analyses which were used to verify that the overall permeability of the liner is less than 10−8 cm/s. It also outlines other testing and instrumentation which has been undertaken to verify the liner permeability and integrity. It is concluded that, to date, the permeability testing and protocol are suitable control procedures to verify compliance with the condition of the Provisional Certificate of Approval that a liner permeability of 10−8 cm/s be achieved. Key words: clay liner, permeability, protocol, quality control, sanitary landfill, sampling, statistical analysis, testing.

Diffusive contaminant transport in natural clay: a field example and implications for clay-lined waste disposal sites

Vertical core samples were obtained from an impervious, unweathered, water-saturated clay deposit beneath a 5-year-old hazardous waste landfill at a site in southwestern Ontario. Sections of the cores were analyzed for chloride and volatile organic compounds. Waste-derived chloride was detected in the clay to a maximum depth of 83 cm below the bottom of the landfill. The most mobile organic compounds were found only to a depth of /approximately/ 15 cm. The downward transport of these chemical species into the clay was the result of simple Fickian diffusion. This study has implications for low-permeability clay liners used at waste disposal sites. For liners of typical thickness (/approximately/ 1 m), simple diffusion can cause breakthrough of mobile contaminants in approximately 5 years; the diffusive flux of contaminants out of such liners can be large.