J.P. Giroud

Leakage through liners constructed with geomembranes—part I. Geomembrane liners☆

Abstract How impermeable are ‘impermeable liners’? All liners leak, including geomembranes, but how much? What are the mechanisms of leakage through liners constructed with geomembranes? To answer these questions, a detailed review of leakage mechanisms, published and unpublished test data, and analytical studies has been carried out with the goal of providing practical design recommendations. In particular, it appears that a composite liner (i.e. geomembrane on low-permeability soil) is more effective in reducing the rate of leakage through the liner than either a geomembrane alone or a soil liner (low permeability soil layer) alone. However, the paper shows that the effectiveness of composite liners depends on the quality of the contact between the geomembrane and the underlying low-permeability soil layer.

Design of soil layer-geosynthetic systems overlying voids

Abstract This paper presents equations, tables, and charts to design soil layer-geosynthetic systems to span voids such as tension cracks, sinkholes, dissolution cavities, and depressions in foundation soils due to differential settlements or localized subsidence. These equations, tables, and charts were developed by combining tensioned membrane theory (for the geosynthetic) with arching theory (for the soil layer), thereby providing a more complete design approach than one that considers tensioned membrane theory only. Design examples are presented to illustrate the solution of typical problems such as: selection of the required geosynthetic properties, determination of the maximum void size that can be bridged by a given system, and evaluation of the load-bearing capacity of a given system.

Rate of leakage through a composite liner due to geomembrane defects

Abstract This paper presents the development of a method to evaluate the rate of leakage through geomembrane defects and, in particular, defective seams, in cases where the geomembrane is placed on a layer of low-permeability soil to form a composite liner. The method is valid for a wide range of liquid heads on top of the composite liner. The method is presented in the form of equations, tables, and charts that can be used for defects ranging from small holes to long cracks. The use of the method is illustrated by examples, and a limited parametric study is presented.

Analysis of geomembrane wrinkles

Abstract In the field, geomembranes expand when they are heated by the sun, and they exhibit wrinkles. The size and spacing of these wrinkles depend on the type of geomembrane. A theoretical analysis presented in this paper gives relationships between various parameters such as height, width and spacing of the wrinkles; modulus, thickness, density and coefficient of thermal expansion of the geomembrane; temperature change; and geomembrane-soil friction. Results of numerical applications are in good agreement with typical observations made in the field, which indicate that stiff geomembranes exhibit large wrinkles and large spacing between wrinkles, whereas flexible geomembranes exhibit small wrinkles that are closely spaced.

Reliability of state of practice for selection of shear strength parameters for waste containment system stability analyses

Abstract In this paper, reliability analyses are performed using the results of slope stability analyses on example waste slopes to address two sources of uncertainty involved in waste slope stability assessments. These include the uncertainty associated with using shear strength parameters derived from non-project-specific sources and the uncertainty associated with the conditions required to make the development of a progressive failure mechanism, and subsequent mobilization of large-displacement shear strengths, possible. The results of the slope stability and reliability analyses performed demonstrate that less reliable or overly conservative designs can result from the use of shear strength parameters obtained from non-project-specific sources and that reliability analyses, even simple ones, provide information that can be used to establish confidence levels in factor of safety calculations. Reliability analysis results also show that slope stability calculations based on the full mobilization of large-displacement shear strengths are conservative since such analyses implicitly assume that a progressive failure mechanism develops. A method is presented that considers one particular progressive failure mechanism for the development of large-displacement conditions. The method provides a framework for evaluating the reliability of slopes where the potential for progressive failure exists.

Geosynthetics in Liquid-Containing Structures

The liquid-containing structures considered herein are those constructed with soil; thus, concrete dams, concrete reservoirs, cavities excavated in rock and steel tanks are not considered. The liquid-containing structures considered include: structures used for liquid storage (e.g. embankment dams, liquid impoundments excavated in soil or surrounded with dikes), structures used for liquid conveyance (canals) and structures used to prevent liquid from migrating into the ground (lined landfills). This chapter addresses analysis and design methods for liquid-containing structures. Required geosynthetic material properties and engineering parameters are addressed. The geosynthetic materials themselves are not discussed, however, and the reader is referred to Chapter 7 for information on this subject.

Quality assurance of geosynthetic lining systems

Abstract Why would the owner of a proposed geomembrane-lined facility agree to a cost increase of 20–40% to pay for quality assurance? Many owners now agree that the benefits of quality assurance are more than worth the extra cost. This paper describes quality assurance related to the design, manufacture, fabrication, installation and use of geosynthetic lining systems. Such lining systems are comprised of geomembranes and other geosynthetics such as geotextiles, geonets and geogrids. The need for third party quality assurance is stressed, i.e. quality assurance should be performed by a party other than the facility owner, the designer, or the geosynthetic manufacturer/installer. A special discussion is devoted to the quality assurance of the design, wherein design review by an independent organization is suggested and examples from actual installations show design mistakes which could have been identified if quality assurance had been provided. This paper is based on experience gained while conducting the quality assurance of a variety of installations as well as forensic investigations at many problem sites.

Yield of scratched geomembranes

Abstract In this paper, it is demonstrated that geomembranes that have a stress-strain curve with a yield peak, such as high-density polyethylene (HDPE) geomembranes, yield at a tensile strain that is significantly influenced by scratches on the surface of the geomembrane. It is shown that scratched HDPE geomebranes can exhibit yield at strains that are one-third to one-half the yield strain of intact geomembranes. The method presented in this paper makes it possible to quantify the reduction in HDPE geomembrane yield strain due to scratches as a function of the scratch depth and the geomembrane thickness. Alternatively, the method can be used to select the thickness of an HDPE geomembrane for a given required yield strain when a certain scratch depth is expected.

Waste Containment Systems for Pollution Control: Part II - Hydraulic Design and Performance

The design and performance of engineered waste containment systems, notably systems for the containment of liquid and gas, are addressed in this paper. These systems are used at landfills (for containment of municipal, industrial, hazardous, and low-level radioactive waste), surface (i.e., liquid) impoundments, and mine storage and leaching pads. Emphasis in this paper is placed on waste containment systems used at modern municipal solid waste (MSW) and hazardous waste (HW) landfills in the United States. In this paper, the term “modern” landfill means a landfill designed to meet current U.S. regulations and constructed and operated according to the state of practice in the U.S. from the mid 1980’s forward. The paper provides a discussion of the following subjects, presented in the order listed: waste and by-products of waste decomposition; basic components of waste containment systems; evaluation of liner hydraulic performance; evaluation of liquid collection layer hydraulic performance; waste containment system field performance; and summary and conclusions.