R. Kerry Rowe

Barrier Systems for Waste Disposal Facilities

1. Basic Concepts. 2. Leachate Characteristics and Collection. 3. Clay Liners: Compaction, Hydraulic Conductivity and Clay Mineralogy. 4. Clay/Leachate Compatibility by Measurement of Hydraulic Conductivity. 5. Flow Modelling. 6. Chemical Transfer by Diffusion. 7. Contaminant Transport Modelling. 8. Evaluation of Diffusion and Distribution Coefficients. 9. Field Studies of Diffusion and Hydraulic Conductivity. 10. Contaminant Migration in Intact Porous Media: Analysis and Design Considerations. 11. Migration in Fractured Media: Analysis and Design Considerations. 12. Geosynthetic Clay Liners (GCLs). 13. Geomembrane Liners. 14. Covers. 15. Geotechnical and Related Design Issues. 16. Integration of Hydrogeology and Engineering in Barrier Design and Impact Assessment. Index.

Clayey Barrier Systems for Waste Disposal Facilities

Basic concepts. Introduction. Overview of barrier systems. Transport mechanisms and governing equations. Complicating factors. Modeling the finite mass of contaminant. Modeling a thin permeable layer as a boundary condition. Hand solutions so some simple problems. Summary. Design considerations. Introduction. Impact assessment. Waste and leachate composition. Leachate mounding and collection. Leakage through liners. Leak detection systems. Landfill capping and the control of infiltration. Choic of barrier system and service life considerations. Geotechnical considerations. Summary. Clayey barriers: compaction, hydraulic conductivity and clay mineralogy. Introduction. Methods of assessing hydraulic conductivity. Compaction-permeability relationships. Clay mineralogy. Clay colloid chemistry. Clay-leachate compatibility by measurement of hydraulic conductivity. Introduction. Soil- MSW leachate compatibility. Compatibility of clays with liquid hydrocarbon permeants. Summary and conclusions. Flow modeling. Introduction. One-dimensional flow models. Analysis of two-and three-dimensional flow. Finite difference approximation. Application of the finite element method to the analysis of plane flow. Boundary element methods. Chemical transfer by diffusion. Introduction. Free solution diffusion (Do). Diffusion through soil. Steady-state diffusion. Transient diffusion. Use of laboratory and field profiles to measure diffusion coefficient De. Diffusion during hydraulic conductivity testing for clay - leachate compatibility. Summary and conclusions. Contaminant transport modeling.Introduction. Analytical solutions. Application of Laplace transforms to develop a finite layer solution for a single layer. Contaminant transport into a single layer considering a landfill of finite mass and an underlying aquifer. Finite layer analysis. Contaminant migration in a regularly fractured medium. Determination of diffusion and distribution coefficients. Introduction. Obtaining diffusion and partitioning/distribution coefficients: basic concepts. Example tests for obtaining diffusion and distribution coefficients for inorganic contaminants. Dispersion at low velocities in clayey soils. Effective porosity. Distribution coefficients and nonlinearity. Effect of leachate composition, interaction and temperature. Diffusion and sorption of organic contaminants. Use of field profiles to estimate diffusion coefficients. Summary and conclusions. Field studies of diffusion and hydraulic conductivity. Introduction. Examples of long-term field diffusion. Examples of short-term diffusion. Hydraulic conductivity of contaminated clay liners. Contaminant migration in intact porous media: analysis and design considerations. Introduction. Mass of contaminant, the ref erence height of leachate, Hr, and the equivalent height of leachate, Hf. Development of a contaminant plume. Effect of base velocity. Effect of horizonta

Durability of HDPE geomembranes

This paper summarizes the basic concepts and mechanisms related to the durability of HDPE geomembranes and discusses the factors influencing the service life of geomembrane liners.Geomembrane durability is addressed in terms of field performance and laboratory test results under various conditions.It discusses their projected service lives that may range from many centuries to less than a decade depending on the type of material and exposure conditions. r 2002 Elsevier Science Ltd.All rights reserved.

Evaluation of side wall friction for a buried pipe testing facility

Abstract Methods of limiting the mobilization of boundary friction during large-scale laboratory testing of buried pipes (geopipes) are investigated. A small scale investigation using a direct shear apparatus examined the effectiveness of different configurations of unlubricated and lubricated geosynthetic treatments intended to reduce the boundary friction mobilized between a steel–soil interface. Results from direct shear tests indicated that applying a double layer of thin polyethylene sheeting lubricated with silicon grease yielded an angle of friction of about 5°, provided that the interface treatment received adequate protection from the backfill material. Tests conducted in the large-scale test facility suggest that this interface treatment successfully limits boundary effects arising from interface friction.

On the hydraulic behavior of unsaturated nonwoven geotextiles

Abstract Geotextiles have been widely used in soil structures for separation, filtration, reinforcing, and drainage. They are often used to provide reinforcement and drainage for retaining walls and embankments. It has been reported, however, that geotextiles may not drain water as effectively as was initially expected. In this study, published data on the hydraulic properties of unsaturated geotextiles are compiled and analyzed in order to highlight the hydraulic characteristics of unsaturated geotextiles. The application of the van Genuchten equations originally developed for the water characteristic curve and the hydraulic conductivity curve of unsaturated soil to unsaturated geotextiles is then examined and discussed. Finally, the drainage from a one-dimensional sand column having a horizontal geotextile layer was analyzed using the finite element method and the van Genuchten equations to assess the utility of this procedure for further study of unsaturated/saturated water flow within the soil–geotextile system.

Predicting biogeochemical calcium precipitation in landfill leachate collection systems.

Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (YH), which relates the carbonic acid (H2CO3) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of YH were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO2-) when present in the leachate. A common yield between total cations bound to CO32- and H2CO3 produced, called the calcium carbonate yield coefficient (Yc), can reconcile the empirical yield coefficient for synthetic and actual leachates.

EFFECT OF WALL GEOMETRY ON THE BEHAVIOUR OF REINFORCED SOIL WALLS

Abstract The effect of geometric parameters such as reinforcement length, number of layers of reinforcement, distribution of reinforcement and wall height on the forces developed in the reinforcement is examined. It is shown that the forces developed are largely independent of reinforcement length for reinforcement to wall height ratios equal to or greater than 0·7. For truncated reinforcement schemes with a ratio of less than 0·7, the forces in the reinforcement increase as the length of the reinforcement decreases. The number of layers of reinforcement was not found to significantly affect the total force required for equilibrium provided the reinforcement stiffness density was the same. The analysis provides theoretical support for the common practice of using truncated reinforcement with equal vertical spacing and length equal to 70% (or greater) of the wall height.

Diffusive Transport of VOCs through LLDPE and Two Coextruded Geomembranes

The diffusive properties of two coextruded geomembranes, one with a polyamide inner core and the other with an ethylene vinyl-alcohol (EVOH) inner core, and a standard 0.53-mm (20-mil) linear low-density polyethylene (LLDPE) geomembrane were examined. Diffusion and sorption laboratory tests were performed to estimate the parameters controlling diffusive migration, including the partitioning, diffusion, and permeation coefficients of the geomembrane in both the aqueous and vapor phases. Results indicate a significant reduction in mass flux through the coextruded geomembranes compared to conventional LLDPE. The EVOH coextruded geomembrane had the lowest permeation coefficients ( Pg ) with a range of ( 2–6 ) × 10−12 m2 s−1 for diffusion from the aqueous phase. These values for EVOH are upper bounds and the actual values may be lower than as stated. The polyamide (nylon) coextruded geomembrane had higher values than for EVOH, with a Pg range of ( 0.7–2.2 ) × 10−11 m2 s−1 from the aqueous phase. The hi...

Reinforced embankments over soft foundations under undrained and partially drained conditions

Abstract The behaviour of geosynthetic reinforced embankments constructed on soft cohesive foundations under undrained and partially drained conditions is examined using an elliptical cap soil model. Consolidation is modelled using Biot theory. The effects of reinforcement stiffness, partial consolidation of the foundation soil during embankment construction and foundation soils with different initial undrained strength profiles are examined. Particular attention is focused on the strains in the geosynthetic reinforcement at working conditions and at embankment failure. The effect of reinforcement on the deformation of the foundation soil is evaluated. It is shown that reinforcement can significantly reduce the maximum lateral deformations, vertical deformation and foundation soil heave during embankment construction. For the conditions examined, partial drainage during construction provides an 11–38% increase in the factor of safety against failure of reinforced embankments relative to that expected under perfectly undrained conditions.

Geosynthetic reinforced embankments on soft clay foundations: predicting reinforcement strains at failure

Geosynthetic reinforced embankments can fail before the ultimate tensile strength of the reinforcement is mobilized. For the purpose of embankment design, engineers must often rely on experience when selectinga reinforcement strain for analysis usinglimit equilibrium methods or resort to complicated numerical methods such as those based on the finite element method. This paper presents a simple procedure for estimatingthe undrained stability of geosynthetic reinforced embankments founded on soft clayey soils where the shear strength increases with depth. Finite element results are summarized in a design chart for establishing geosynthetic reinforcement strains suitable for design. The procedure is illustrated using worked examples and tested against a well documented case history. r 2003 Elsevier Science Ltd. All rights reserved.