SPECIAL ISSUE ON GEOSYNTHTIC CLAY LINERS
Volume 11, Nos 3 & 4, of Geosynthetics International is a special double issue devoted to geosynthetic clay liners (GCLs). GCLs are manufactured products consisting of bentonite clay bonded to a layer, or layers, of geosynthetic material. In the 22 years since the GCL was invented, acceptance of these products has grown to the point where they are now commonly specified in the design of waste disposal facilities and other facilities requiring hydraulic barriers. Acceptance has been rapid because GCLs offer many advantages over compacted clay liners, not the least of which is lower cost for many applications. Equally rapid developments in manufacturing, testing, design, construction, and the regulatory environment have sparked research on many issues related to GCL performance. These Special Issues contain some of the latest research on the engineering behavior of these unique barrier materials.
These Special Issues began with the writing of a state-of-the-art report on GCL shear strength. After inviting Professor Stark to join me in this effort, I approached leading international experts in GCL research and invited them to submit abstracts for possible papers. These invitations produced 13 abstracts from which 12 technical papers were ultimately accepted for publication after each received rigorous peer review by two or more anonymous reviewers. These Special Issues provide our readers with coverage of a wide range of topics including: shear strength, stability analysis, hydraulic performance, contaminant migration, gas permeability, bentonite migration, and bentonite hydration. The scope and content of several papers is beyond that typical for a journal article as the intent was to provide contributing authors the flexibility to submit comprehensive papers if desired.
The papers in this Special Issue can be grouped into common themes:
Four papers focus on shear strength and stability of GCLs. Fox and Stark present a state-of-the-art report on GCL shear strength. Essential concepts of shear stress–displacement behavior and shear strength interpretation are presented, including long-term performance and selection of design failure envelopes, followed by detailed discussions on the laboratory measurement of the shear strength of GCLs and GCL interfaces. Chiu and Fox present information compiled from a large database of internal and interface shear strengths of unreinforced and needle-punched GCLs. Gilbert, Wright, Shields, and Obermeyer present direct shear data to establish a lower-bound drained shear strength envelope for any type of GCL or GCL interface in landfill base liners. McCartney, Zornberg, Swan, and Gilbert assess the impact of variability in laboratory GCL shear strength test results on conventional design methodologies using reliability-based stability analyses.
Four papers deal with hydraulic and transport issues for GCLs. Kolstad, Benson, Edil, and Jo present the results of a series of swell and hydraulic conductivity tests conducted with aggressive inorganic solutions on a dense prehydrated unreinforced GCL and a heat-bonded needle-punched GCL. Benson, Jo, and Abichou present a forensic investigation of leakage from two lagoons with composite liners consisting of a thin geomembrane laminated to one side of a geotextile-supported GCL. Lake and Rowe present test results and analyses of the diffusion of five common volatile organic compounds through a needle-punched GCL. Rowe and Brachman assess the equivalency of composite liners containing a geomembrane and a GCL to traditional composite liners containing a geomembrane and compacted clay in terms of the potential contaminant impact on a receptor aquifer.
One paper addresses gas permeability of GCLs. Bouazza and Vangpaisal present data from a series of gas permeability tests on a partially hydrated needle-punched GCL subjected to varying hydration conditions and magnitudes of strain.
One paper addresses bentonite migration in GCLs after placement. Stark, Choi, and Akhtarshad present field case histories of bentonite migration in GCLs and analyses of the impacts of such migration on GCL hydraulic equivalency and contaminant transport.
Two papers focus on hydration of bentonite within encapsulated GCLs. Giroud and Daniel present analyses of liquid migration in a bentonite layer due to defects in the encapsulating geomembranes. In a companion paper, Giroud, Thiel, and Kavazanjian present an analytical method to evaluate the extent of the hydrated area within such a bentonite layer as a function of time and address the impact of hydrated area on shear strength.
These Special Issues of Geosynthetics International would not have been possible without the patience and dedication of the contributing authors. I would also like to gratefully acknowledge the assistance of R. J. Bathurst, Editor, and the contributions of the many reviewers who took the time to ensure that each paper met the high technical standards of Geosynthetics International.
