Joseph P. Martin

Shear strength parameters between geomembranes and cohesive soils

Abstract This paper focuses on the shear strength of various geomembranes and a number of different cohesive soils. The data base is felt to be necessary since geomembranes used in solid waste disposal are often placed directly on low permeability clay soils. Adapted direct shear tests were performed allowing for a determination of adhesion and friction angle values. It was seen that the adhesion of the soil to the geomembrane is significantly reduced from the cohesion value of the soil itself, unless the geomembrane is very soft or textured. Conversely, the friction angle at the interface between the geomembrane and the soil is relatively high, at least for the normal pressures used in these tests. The information presented is felt to be the type necessary for a number of practical design considerations.

Water and air transmissivity of geotextiles

Abstract The in-plane flow characteristics of both water and air in needled, nonwoven geotextiles have been evaluated in this study. Transmissivity (equal to permeability times fabric thickness) versus applied normal stress on the fabric has been measured in a radial flow device for different fabrics and for different thicknesses of a given fabric. The transmissivity response in each case was seen to decrease with increasing stress until a residual value was reached. In none of the cases did the fabric compress to the point where flow was completely shut off, even though stress levels of 2500 psf were applied. In turn, the calculated geotextile permeability varied from a fine gravel to a medium sized sand. Planar air flow in geotextiles has been found to be in excess of two orders of magnitude greater than water flow under comparable conditions. Air flow through partially and fully saturated fabrics is shown to be of little practical interest since the air easily moves around the water in the fabric voids or displaces it entirely. The need for transmissivity test standardization for all types of geotextiles and geotextile composite systems is expressed.

Geotechnical design considerations for geomembrane lined slopes: Slope stability

Abstract The design of geomembrane lined containment systems is a multi-faceted problem requiring the combined talents of many diverse disciplines. One of these disciplines is that of geotechnical engineering, within which falls the topic of soil slope stability. Since the integrity of the liner is dependent on this support system its proper design is of obvious importance. This paper addresses various approaches of soil slope stability and also includes the stability of cover soils which are often placed above the geomembrane for its protection. Related topics of anchor trench design at the top of the slope and of post-construction stability problems will be treated in subsequent papers.

The influence of vadose zone conditions in groundwater pollution: Part II: Fluid movement

Abstract This is the concluding portion of a two-part review illustrating the influence of the vadose zone (i.e., soil materials located above a water table) on groundwater pollution. Seepage from landfills, lagoons, storage areas and land treatment sites invariably must pass through this region before entering an aquifer. In general, contaminant concentrations are highest near the source. Much of this zone is unsaturated, so that leachate and wastewater may have access to oxygen and be in close contact with solid particle surfaces. Consequently, conditions in the vadose zone affect both the seepage rate and the environment for attenuation of contaminant species. The focus of this paper is on the application of Darcys formula to describe the flow of water, leachate and other fluids under both saturated and unsaturated conditions. The discussion is presented in a state-of-the-art format. Individual topics include the material properties that influence flow and the relationship between seepage rate, fluid pressure and the degree of saturation. To illustrate these concepts, five generalized examples are presented. They describe a wide range of practical situations, including: • steady vertical seepage • flow in the vadose zone parallel to a water table • development of groundwater mounds under liquid filled impoundments • wetting front advance through homogeneous soil • wetting front advance under lined impoundments These examples, and the principles from which they are derived, can be used both in analysis of existing situations and in design and operation of new facilities. This paper is a companion to one previously published which discussed static conditions in the vadose zone.

The influence of vadose zone conditions on groundwater pollution: Part I: Basic principles and static conditions

Abstract The significance of the vadose soil zone (i.e., above a water table) is of the utmost importance in groundwater pollution problems. Much of this zone is unsaturated, such that fluid movement and contaminant attenuation conditions are favorable for mitigation of aquifer pollution. In this paper, the basic principles of moisture retention and the implications for leachate control are described in a state-of-the-art format. To illustrate the use of these concepts six generalized examples are presented. They cover a wide range of practical situations, including: • vadose zone storage • land treatment of wastewater and sludges • waste dewatering • hydrocarbon spill storage • capillary break situations • air and water drainage under liners Since this paper treats only the static condition, a companion paper will be offered shortly dealing with leachate flow and seepage in a wide range of applications.