Rudolph Bonaparte

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 To answer these questions, a detailed review of leakage mechanisms, published and unpublished test data, and analytical studies has been carried out with the goal of providing practical design recommendations.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.

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.

Preliminary results of composite liner field performance study

Abstract This paper presents preliminary results of a study of the field performance of composite liners. The purpose of the study is to evaluate the ability of composite liners to contain municipal solid waste (MSW) leachate. The paper presents data for double-lined MSW landfills having composite top liners consisting of a geomembrane (GMB) upper component and a compacted clay liner (CCL) lower component. Data on flow volumes and flow constituents for the leachate collection and removal system (LCRS) and the leakage detection system (LDS) components of the double liner system are analyzed to assess whether leakage has occurred through the composite top liner. Data for nine MSW landfill cells with monitoring periods of up to eight years are presented. Preliminary results indicate that the nine composite liners are performing well and are effective in containing MSW leachate.

LONG-TERM ALLOWABLE TENSILE STRESSES FOR POLYETHYLENE GEOMEMBRANES

Abstract The objective of this paper is to present a rational methodology for establishing long-term allowable tensile stresses for polyethylene geomembranes used in waste-containment applications. Procedures currently used in the USA do not account for all of the factors that may significantly affect this parameter. The proposed procedure is intended to address this limitation by providing a framework to account for time, temperature, exposure environment, seam response, and boundary-stress and deformation conditions. The proposed procedure is conceptually similar to procedures used to establish the long-term allowable tension for geosynthetic reinforcement. An example of the use of the procedure is provided.

Reinforcement Extensibility in Reinforced Soil Wall Design

There are many types of reinforcing materials and systems available for the construction of reinforced soil walls. Of the many types, the Reinforced Earth system developed by Vidal (1966) in France has predominated and has provided the basis for most theoretical and empirical knowledge of the behavior of reinforced soil walls. The Reinforced Earth system has a number of distinguishing characteristics that include: steel reinforcing elements that have tensile moduli on the order of 2 × 108 kPa (3 × 107 lbs/in2); reinforcing elements that are discrete strips, approximately 50 mm (2 in.) wide and 5 mm (0.2 in.) thick; and concrete facing (skin) elements that can individually undergo limited translation and rotation in response to movements in the reinforced fill or settlements of the foundation soils.

Effect of soil compaction conditions on geomembrane-soil interface strength

Abstract A laboratory investigation was recently undertaken to evaluate the shear strength of the interface between a cohesive soil used for linear construction and a high-density polyethylene (HDPE) geomembrane. In the investigation, the interface shear strength was measured in a direct shear apparatus. The compaction water content and dry unit weight of the soil were varied in each test. It was found that the shear strength of the interface between these two materials is strongly affected by the compaction water content and dry unit weight of the soil. It is concluded from the test results that the soil compaction conditions strongly influenced the interface shear strength and this factor, among other, should be carefully considered during design.

Current status of the Cincinnati GCL test plots

Abstract This paper describes the design, layout, construction and current status on the performance of fourteen full scale test plots targeted at assessing the internal shear strength of GCLs in landfill cover applications. Five different commercially available GCLs from four manufacturers were used in the study. Each test plot is two geosynthetic clay line roll widths wide, with lengths of 29m (95 ft) on the 3(H)-to-1(V) (horizontal-to-vertical) slopes and 20m (67 ft) on the 2(H)-to-1(V) (horizontal-to-vertical) slopes. The plots are being monitored with numerous deformation ‘telltales’ as well as subgrade and GCL moisture gages. Two slides occurred shortly after construction. Both involved the upper surfaces of the GCLs against the overlying textured geomembranes. The slides were clearly the result of bentonite lubricated interfaces and (although of interest) did not relate to the internal shear strength focus and goals of the project. Upon inducing internal shear stress in the GCLs by cutting all of the overlying geosynthetics, the deformations have been small except for one plot. This plot involved a unreinforced bentonite GCL, sandwiched between two geomembranes. It was sampled and found to have a large region of unexpected and excessively high moisture content. Subsequently, the test plot slid, the interface being the upper geomembrane against the bentonite of the GCL. The test plot was constructed a second time and the current response is more in keeping with the anticipated behaviour. Other than these slides, however, all of the other GCL plots appear to be stable. If the internal stability of the GCLs continue, it can be assumed that the 2(H)-to-1(V) slopes have a factor-of-safety of 1.0 or greater. This being the case, the 3(H)-to-1(V) slopes have a factor-of-safety of 1.5 or greater. While this hypothesis is still being substantiated, it speaks well for the internal shear strength of the GCLs used in the study when properly installed. The project is ongoing as of, the writing of this paper.