George R. Koerner

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.

Leachate flow rate behavior through geotextile and soil filters and possible remediation methods

Abstract This paper presents flow rate data in the form of system permeability values using various filtration schemes involving both geotextiles and natural soil filters. The tests were conducted over a 20-month period using six different types of leachate. In total, 96 different combinations were evaluated. In all cases, permeabilities decreased over time due to a combination of sediment clogging and/or biological clogging. When a steady state permeability value appeared to be reached, after approximately 6 months, the first of four remediation schemes were attempted. It was seen that water backflush is the most effective in reinstituting high flow rates, followed by backflushing with leachate and nitrogen gas. The least effective remediation scheme was vacuum extraction. Biocide treated geosynthetics were also evaluated, but results were inconclusive. This was due to the long times required and/or the remnants of the micro-organisms which could not pass through the various filtering systems. The long-term minimum permeability values were not identified, nor were the design required permeabilities for the various landfills, in question. These important items are currently being investigated.

Assessment of HDPE geomembrane performance in a municipal waste landfill double liner system after eight years of service

Abstract In the late 1970s and early 1980s, environmental regulations were upgraded in a general national movement to effect secure management of our municipal and residual solid wastes. The new regulations required varying combinations of natural and/or synthetic barrier and drainage layers to prevent the unrestricted release of contaminants. The acceptable barrier materials included synthetic flexible membrane liners (FMLs) of various types. One of those most commonly used has been high-density polyethylene (HDPE) geomembrane. HDPE has been selected because of its good chemical resistance characteristics, among others. Background compatibility testing has shown the HDPE geomembrane to be extremely resistant to the leachates that are generated by municipal and residual solid waste landfills. The background testing for design has generally been based on relatively short-term tests that are conducted under extreme conditions to ‘forecast’ service life. Recently, a municipal solid waste landfill double liner system that was constructed in 1988 was exhumed. The HDPE geomembranes of this liner system had been exposed to varying degrees of leachate since 1989. Samples of the HDPE were extracted from the in-place liner system and were laboratory-tested for physical, mechanical and endurance properties. The selected suite of tests duplicated the test protocol conducted in 1988 as part of the liner system construction quality assurance (CQA) program. The results of this testing show that the HDPE properties are still within the range of data generated by the original testing in 1988. No degradation in properties was indicated by this testing program. The HDPE had been exposed to the leachate, methane, and static and dynamic stresses for approximately 8 years. The results of this test program support the design selection of HDPE as the synthetic barrier component of this landfill liner system.

Performance Tests for the Selection of Fabrics and Additives When Used as Geotextile Bags, Containers, and Tubes

There are two performance tests available for the selection of fabrics and additives when contemplating a geotextile bag, container, or tube application. They are the “hanging bag test” and the “pillow test.” Both tests are described in this paper along with data generated by their use. While both can be used for selection purposes, the advantages of the pillow test over the hanging bag test are quite compelling. Items favoring the pillow test are much smaller size, need for less dredged or slurried infill material, better field simulated orientation, and the capability of monitoring hydraulic head versus time behavior. This last item is most important since dredging pressures are always involved and the simulated behavior of the pillow test gives good insight into the anticipated behavior of the full-scale application.

Properties of exhumed HDPE field waves

Abstract HDPE geomembranes are the most widely used components of liner and cover systems of landfills throughout the world. Millions of square meters of HDPE geomembrane have been used as hydraulic barriers over the past twenty years. It is usually assumed that HDPE geomembranes lie flat against soil subgrade. Unfortunately, this is not always the case. It is obvious that waves (also called wrinkles) compromise the concept of intimate contact but equally important, they may influence the properties of the geomembrane. The purpose of this paper is to examine if waves remain in the backfilled geomembrane and to what extent they influence performance properties.

Geotextiles used as flexible forms

Abstract Traditionally, wood and metal have been used to contain concrete or cementatious grouts in the forming of constructed facilities. These materials result in rigid forms which are positioned and fixed in location until the material placed in them adequately cures and has sufficient strength for self-support. While the constraint of a rigid form is an obvious advantage in building a concrete wall or footing to exact line and grade, it is a decided disadvantage in a number of other applications. These situations, which can capitalize on the use of a flexible form made from a geotextile, are described in this paper. As will be seen, all of the applications bear heavily on infrastructure enhancement and remediation.

Geosynthetic use in trenchless pipe remediation and rehabilitation

Abstract The traditional method of repairing broken or otherwise nonserviceable underground pipes is by excavation (usually requiring sheeting and shoring), pipe removal, pipe replacement, backfilling and then restoration of the site to its original condition. With the advent of an array of trenchless pipe construction techniques, the remediation and rehabilitation of underground pipes (particularly sewers) has drastically changed. These trenchless methods only require access at periodic locations (often at existing manholes) thereby eliminating most of the objections associated with traditional construction operations, e.g. congestion, traffic, dust, mud, debris, noise, etc. The currently used trenchless techniques for pipe remediation and rehabilitation are described in this paper. They will be accompanied with commentary on their respective advantages and disadvantages. Typical costs and other details will also be presented. Focus is placed on those systems which employ geosynthetics or other polymeric materials. While the main application area is on underground sewer pipelines, the transition of the presented material to other underground pipeline and tunnel situations can readily be made.

Field Performance of Geosynthetic Highway Drainage Systems

This paper presents field results from a three year study focused on the performance of geosynthetic materials in transportation related drainage applications. The application areas of interest were mainly highway edge drains, although selected retaining wall drains and erosion control systems were also involved. Included in the study are geotextile filters, geocomposite edge drains, geocomposite sheet drains and, to a limited extent, plastic pipe. In many instances, the geotextile was observed to be the key element in the overall success or failure of the system. Thus the geotextile, serving in a primary function as a filter was the major focal point of the investigation. The paper presents the results of exhuming ninety-one (91) field sites in seventeen (17) states throughout the United States. The results give a clear assessment of geosynthetic drainage systems from a long-term field perspective. Furthermore, it allows for specific recommendations to be made to avoid those situations where problems occurred. In a subsequent paper in these Proceedings the results will ultimately be used to challenge the necessary design formulas currently available for geotextile filters in highway drainage applications.

Index Puncture Resistance of Geomembranes Using Various Protection Geosynthetics

The puncturing of geomembranes by stones is unfortunately not uncommon. In order to prevent its occurrence, various geosynthetics have been used as protection materials. Needle punched nonwoven geotextiles (of various unit weights), geonet drainage composites, and geosynthetic clay liners have been used, and all are evaluated in this laboratory puncture study. Results from three standardized puncture test methods (tapered, pin, and pyramid shaped end probes) are compared to one another. The results show that all geomembranes are susceptible to puncture, with increasing thickness providing some, but limited, improvement. Geotextiles clearly show improved puncture protection, and the improvement is in linear proportion to their increasing unit weights. Geonet drainage composites also show improvement essentially in proportion to the unit weights of the geotextiles affixed to the surfaces of the geonet core. Geosynthetic clay liners also provide protection, again in proportion to the unit weight of the associated geotextiles, particularly when the bentonite is hydrated.

Geotextile Filter Failures Under Challenging Field Conditions

This paper reviews seventy (70) field failures involving geotextile filters. They are grouped into four categories: inadequate design, atypical soils, unusual permeants, and improper installation. In the first category are poor fabric selection, poor fabric design, socked drainage pipe and reversing flow conditions. In the second category are fine grained soils, gap-graded soils, dispersive clays and ochre. In the third category are sludges, turbid water, alkaline water, leachates and agricultural waste liquids. In the fourth category are lack of intimate contact and glued surfaces. While not the topic of the paper, per se, most of these same conditions are known to be troublesome to soil filters as well as to geotextile filters. In spite of such obvious problematic conditions, however, none of the four standardized long-term flow tests were conducted during the design phase for any of the case histories. Clearly, such situations can be simulated in the laboratory so as to avoid such occurrences in the future. That said, this paper aims to draw attention to those geotextile filter failures which can be readily avoided with proper attention to design, testing and construction.