Field tests were conducted to assess installation damage for an adhesive-bonded, and a needle-punched, geosynthetic clay liner (GCL). GCL panels were laid on a prepared subgrade and covered to varying thicknesses with clean angular sand and clean angular gravel. After hydration, bulldozers were driven over the test plots. GCL samples were then carefully exhumed and laboratory tests were performed to assess damage according to product type, cover soil type, cover soil thickness, bulldozer type, and number of bulldozer passes after hydration. Visual observations and laboratory test results indicated that the products generally performed well during installation. Damage to the geosynthetic components of the GCLs was minor for a cover soil thickness of 305 mm or greater. Mass per unit area measurements indicated that bentonite migration was insignificant for nearly all specimens; the only exception was the adhesive-bonded GCL covered with gravel and subjected to 10 passes of a medium-weight bulldozer after hydration. No failures were observed for installation conditions that met the guidelines of ASTM D 6102 and the manufacturer. Compared to similar investigations for other geosynthetic materials, installation damage studies for GCLs are unique because of the sensitivity of these products to hydration and overburden stress conditions and the need to quantify bentonite migration due to stress concentrations.

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A large direct shear machina for static and dynamic shear strength testing of geosynthetic clay liners (GCLs) and GCL liner systems is described. The machine tests rectangular GCL specimens measuring 305 × 1067 mm and has a maximum shear displacement of 254 mm, which is sufficiently large to allow for the measurement of residual or near-residual shear strengths in most cases. The basic design concept for the device is to shear a GCL specimen between a bidirectional pullout plate and a stationary reaction plate, each covered with an aggressive gripping surface. The pullout plate is driven by a computer-controlled hydraulic actuator. The maximum normal stress is 2000 kPa, the maximum shear stress is 750 kPa, and the shearing system is capable of imposing general stress-controlled or displacement-controlled dynamic loading to a test specimen. The actuator has a maximum frequency of 4 Hz for sinusoidal loading with a displacement amplitude of 25 mm. The maximum displacement rate for burst loading (i.e., single thrust) at zero force is 1 m/s. The paper describes four main components of the machine: (1) the shearing system; (2) the normal stress and vertical displacement measurement system; (3) the specimen hydration system; and (4) the process control and data acquisition system. The performance of the machine is illustrated using displacement-controlled test data for the static and cyclic internal shear strength of a hydrated needle-punched GCL.

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For the most up-to-date product information, please visit our website, www.cetco.com. A wholly owned subsidiary of AMCOL International Corporation. The information and data contained herein are believed to be accurate and reliable, CETCO makes no warranty of any kind and accepts no responsibility for the results obtained through application of this information. CURRENT RESEARCH ON DYNAMIC SHEAR BEHAVIOR OF GEOSYNTHETIC CLAY LINERS Geosynthetic clay liners (GCLs) have seen increasing usage in civil engineering applications. However, little is known about their response to dynamic stresses during seismic events. There is a concern over the internal shear strength of GCLs and interface shear strength of GCLs with adjacent materials under these conditions. A new type of shear box capable of applying seismic ground motions has been constructed at Ohio State University. The shear box can test rectangular GCL specimens measuring 0.3 × 1.1 m (12 × 42 in.). The device has a maximum shear displacement of 254 mm (10 in.), a maximum normal stress of 2,400 kPa (50,000 psf), a maximum shear stress of 750 kPa (15,700 psf). In the case of sinusoidal shearing, the maximum frequency corresponding to a displacement amplitude of 25 mm (1.0 in.) is 5 Hz. This paper, presented at the GRI-19 Conference, describes the objectives of the research program, the equipment, initial dynamic shear testing results, and further dynamic shear tests planned within the next two years.