State-of-the-art report: GCL shear strength and its measurement (original) (raw)
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Shear Behavior of Reinforced Geosynthetic Clay Liners
Ring shear tests were performed to evaluate the effect of bentonite on theinterfaceshearstrengthbetweenageomembraneandareinforcedgeosyntheticclay liner (GCL), and the internal shear behavior of reinforced GCLs. The tests yielded an interfaceshearstrengththatisinagreementwiththeback-calculatedshearstrengthval- ues from two test pads that deformed at the U.S. Environmental Protection Agency GCL Test SectioninCincinnati, Ohio, USA. The ring sheartests showedthat the inter- nal shear strength of reinforced GCLs depends on the following two factors: (i) resist- ance againstreinforcing fiberpull-out and/ortearing; and,(ii) shearstrength ofbenton- ite. The laboratory tests indicate that fiber resistance is the predominant internal shear strengthfactor.Recommendationsarepresentedfortherateofshearthatshouldbeused for internal shear testing of reinforced GCLs.
Long-term shear strength of geosynthetic clay liners
Geotextiles and Geomembranes, 2008
Geosynthetic clay liners (GCLs) often have a sandwich-like multilayer structure, e.g. bentonite encased between two geotextile layers connected by fibers or yarns, either by needle-punching or stitch-bonding. Therefore, the internal shear strength of the GCL depends on the strength of reinforcing fiber bundles or yarns and their anchoring strength in the cover and carrier geotextiles. When used on long and steep slopes and covered with thick soil layers, the GCL is permanently exposed to a combined action of compressive and shear stress. Such load conditions are characteristic for landfill covers and the slope stability of the overall cover system in the long run strongly depends on the long-term internal shear strength of the GCL. A new test method was developed to study this long-term shear behavior. The focus was not only on creep, as it is normally done, but on aging effects. The shear test devices allow the measurement of creep curves and times-to-failure at elevated temperatures in different media (tap water and de-ionized water). In this publication, the main findings of the experiments on needle-punched GCLs with and without thermal treatment are summarized. Tap water as a test medium was essential to ensure sodium to calcium ion exchange in the bentonite layer. Under this condition extremely long test durations without failure were achieved. Sliding failure occurred when de-ionized water was used. Two failure modes were observed: brittle failure of the GCLs with thermal treatment and slow disentanglement of fiber bundles for untreated GCLs. Short-term shear strength (e.g. peel strength) is unrelated to the actual long-term shear strength, i.e. to the times-to-failure achieved in long-term shear strength test. Hence, short-term shear strength alone will not provide reliable dimensioning data for product design and choice of resins. Therefore, the often suggested approach, namely, restriction to short-term tests only and application of factors of safety, is challenged by these results.
Effect of Specimen Conditioning on Geosynthetic Clay Liner Shear Strength
Specifications for laboratory shear strength testing of geosynthetic clay liners (GCLs) must replicate field conditions while still accounting for time and cost considerations. A database of 414 GCL in- ternal and 534 GCL-geomembrane (GM) interface shear strength results has been assembled. Specifically, the results of large-scale direct shear tests conducted by a single independent laboratory are evaluated to de- velop guidelines on specimen conditioning. It was found that both the GCL internal and interface peak shear strengths decreased with increasing time of hydration (th). However, the GCL internal shear strength did not change for th beyond 48 hs and the GCL-GM interface shear strength did not change for th beyond 24 hs. The normal stress used during hydration affected significantly the peak shear strength due to bentonite swelling. Hydration under low normal stress followed by consolidation led to similar GCL internal peak shear strength as hydration under high normal stress...
Effect of Shear Displacement Rate on Internal Shear Strength of a Reinforced Geosynthetic Clay Liner
Geosynthetics International
Torsional ring shear tests were performed to evaluate the effect of shear displacement rate on the internal shear strength of a needle-punched geosynthetic clay liner (GCL) under different normal stresses. The test results suggest that the internal shear strength of the needle-punched GCL depends on the following three factors: (i) resistance against reinforcement fibers pulling out and/or tearing; (ii) amount of positive pore-water pressure induced during shear; and (iii) bentonite water content at the time of shearing. The laboratory tests indicate that the net effect of these three factors result in the peak internal shear strength being less sensitive to shear displacement rate at normal stresses between 200 and 400 kPa than at normal stresses less than 200 kPa. Shear displacement rate appears to have little influence on the residual internal shear strength regardless of normal stress. The amount of shear displacement required to reach the peak and residual internal shear streng...
Interface Shear Strength of Geosynthetic Clay Liner (GCL) and Residual Soil
International Journal on Advanced Science, Engineering and Information Technology, 2012
In this study, direct shear box with dimension of 100 mm x 100 mm was used to determine interface shear strength of a GCL and compacted residual soil at optimum moisture content. The tests were carried out using dry GCL sample at shearing rate of 0.5 mm/min. Normal stresses used were between 100 kPa to 300 kPa to represent the depth of 20 meters of solid waste (15 kN/m 3). The needle-punched GCL was tested for both sides, woven and non-woven. Results showed that the residual soil, classified as CL according to the Unified Soil Classification System (USCS) with a hydraulic conductivity of 7.05 to 5.54 x 10-9 m/s, was suitable to be used as compacted clay liner (CCL). Test results on the interface shear strength of woven and non-woven GCL with residual soil in terms of internal friction angle were 33° and 37°, respectively.
Large-Scale Shear Tests on Interface Shear Performance of Landfill Liner Systems
Geosynthetics in Civil and Environmental Engineering
Interface shear performance of various landfill liner systems were evaluated for landfill stability by conducting large scale shear tests. Testing program covers the interfaces between (1) geosynthetics (geomembrane (GM) sheet (HDPE and PVC) and non-woven geotextile) and subsoil, (2) geosynthetics and compacted clay liner (CCL), and (3) GM and geotextile. The focus of this paper is placed on interface shear performance under both as installed condition (dry for geosynthetics and optimum moisture content for CCL or subsoil) and saturated / wet condition, since landfill liner system is often subjected to saturated / wet condition due to the higher water retention capacity of CCL as well as the contact to leachate and/or groundwater. For geotextile-GM interface, there is no significant effect on the interface shear strength. The saturated CCL-GM interface had lower shear strength compared to the interface under as installed condition, although the shear performances of CCL-geotextile interface under both conditions are similar to each other. For the interfaces between geosynthetics and subsoil, the frictional resistance of HDPE with textures surface had a significant drop from 23 to 15 degree in the saturated / wet condition.
Out-of-Plane Tensile Behavior of Geosynthetic Clay Liners
Geosynthetics International, 1996
Presented in this paper is the out-of-plane tensile behavior of a variety of geosynthetic clay liners (GCLs). Tensile response curves indicate that GCL strength is largely dependent on the carrier material types from which the GCL is manufactured. Fiber reinforcement effects as well as orientation effects were relatively small for this type of test. The effects of hydration and seams were also assessed. The study shows that GCLs can withstand considerably greater out-of-plane deformation than compacted clay liners (CCLs). Review of the results indicates that GCLs should be considered over CCLs for use as barrier layers where differential subsidence is anticipated.
Shear Behavior of an Unreinforced Geosynthetic Clay Liner
Geosynthetics International
Dry and hydrated specimens of an unreinforced geomembrane-backed geosynthetic clay liner (GCL) were sheared against a textured geomembrane using a torsional ring shear apparatus to study the shear behavior of geomembrane encapsulated bentonite. Shearing of the dry GCL against a textured geomembrane at high normal stresses resulted in failure occurring within the GCL adhesive that attaches the bentonite to the geomembrane backing and not the GCL bentonite/geomembrane interface. This type of failure occurred when both smooth and textured geomembranes were used as the GCL backing material. Conversely, shearing of the hydrated GCL against a textured geomembrane resulted in failure occurring at the GCL bentonite/textured geomembrane interface. The order of hydration and normal stress application was found to significantly affect the GCL/textured geomembrane interface shear strength. The mobilized shear strength of the GCL/textured geomembrane interface does not equal the drained shear st...
International Journal of Geosynthetics and Ground Engineering
Geosynthetics form an integral part of engineered municipal solid waste (MSW) landfill lining systems, as they provide cost saving and technical benefits. Their introduction in lining systems, however, has presented new potential interfaces for shear failure especially on bases and on side slopes of engineered MSW landfills. In the laboratory, interface shear strength parameters used in slope designs of landfill lining systems are determined through single-interface testing configurations as per ASTM D5321-20 and D6243-20 standards. However, single-interface testing configurations do not provide a clear understanding of shear strength transfers among the lining components and does not aid in pin-pointing the interface facilitating failure especially when a multi-layered lining system has been proposed. Multi-interface testing configurations present an alternative that may address such limitations. But there is minimum information available on this type of testing as it is not stipul...