Comparative Assessment of Single- and Double-Interface Shear Tests of MSW Landfill Liners Using Large Direct Shear Equipment (original) (raw)
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The design of a competent basal lining system is crucial in ensuring a long-lasting and functional engineered municipal solid waste (MSW) landfill. However, due to the inclusion of numerous geosynthetics and geomaterials forming a multi-layered lining system, there rises an uncertainty on determining the critical or weakest interface. This is exacerbated by the different properties offered by these lining materials and their inter-crossing functions in landfills. According to ASTM D5321-20 standard, the interface shear strengths used in design of bases and side-slopes of lining systems are determined through a single interface testing configuration. However, minimal research has been done to evaluate the consequences of multi-interface testing configurations on the minimum factors of safety (FoSmin). The present study was thus conducted to further investigate this phenomena while establishing the appropriateness of double interface testing configuration using large direct shear equi...
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.
Interface shear strength variability and its use in reliability-based landfill stability analysis
Geosynthetics International, 2006
Failure of modern landfills by slippage of lining materials and waste bodies is not uncommon. The majority of failures are controlled by slippage at interfaces between lining components. Information on variability of interface shear strength is required both to carry out limit equilibrium stability analysis using characteristic shear strengths and to analyse the probability of failure. Current practice is to carry out a limited number of site-specific tests, and this provides insufficient information on the variability of interface strength for design. A summary of measured strengths and an assessment of variability are presented for seven generic interfaces common in landfill lining systems. This combines values from the international literature, from an internal database, and from the results of repeatability testing programmes. The implications of variable shear strength are examined though failure probability analysis for two common design casesveneer and waste body slippage -and this adds to the small number of studies published previously. The reliability analyses show that relatively high probabilities of failure are obtained when using variability values from the literature and an internal database, even when factors of safety > 1.5. The use of repeatability data produces lower probabilities for typically used factors of safety, although they are still higher than recommended target probability of failure values.
Influence of Surface Texture on the Interface Shear Capacity of Landfill Liner
Geomembrane is one of the most widely used geosynthetics in various civil engineering applications. Its primary function is to act as a barrier for liquid and/or vapour. Smooth geomembrane is frequently used in combination with different soils, and however due to its low surface roughness, the main concern in the design is to ensure adequate shear capacity along the smooth geomembrane/soil interface. The use of smooth geomembrane will lead to low interface shear capacity between landfill liner components which can be considered as one of the major factors in the landfill slope stability failures. Modification of HDPE geomembrane from smooth surface to textured surface is therefore required to improve interface shear capacity of landfill liners. In this study, several interfaces of landfill liner components were tested by using large scale shear box. The combinations used were (1) Sand:Bentonite (100:5)/Smooth HDPE; (2) Sand:Bentonite (100:10)/Smooth HDPE; (3) Sand:Bentonite (100:5)/...
International Journal of Geosynthetics and Ground Engineering
Landfill liners are critical components of waste containment systems that are designed to prevent the migration of pollutants into the environment. Accurate measurement of the shear strength of soil–geosynthetic and geosynthetic–geosynthetic interfaces is essential for designing safe and cost-effective landfill liners. This paper presents a comparative study of the shear strength parameters of single and multi-layer interfaces using a Large Direct Shear Apparatus (LDSA). The study aimed to investigate the effects of using different testing configurations on the Peak and Large Displacement (LD) strengths of the interfaces and to identify the test configuration that provides the most critical shear strength results. A “305 × 305 mm” LDSA was used to perform interface shear tests in saturated conditions with applied normal stresses ranging from 50 to 400 kPa. The results showed good agreement between strength envelopes derived from single and multi-layer interface tests for the materia...
Detritus
One of the crucial aspects in design of a landfill capping is the interface behavior between the different layers of the cover system, from levelling layer above waste up to the topsoil. Design guidelines and international codes require a geotechnical stability analysis to be performed along every interface. The critical interface is the one which gives the minimum shear resistance, in terms of friction angle and adhesion. Evaluation of the correct values to be used is then essential. Shear resistance at the interface between different geosynthetics or between a geosynthetic and a soil can be measured through laboratory tests. Testing methods are EN ISO 12957-1 and ASTM D5321 (for direct shear test) and EN ISO 12957-2 (for inclined plane). The paper briefly describes direct shear and inclined plane testing methods and enhances pros and cons. In the last 25 years the authors have coordinated a great number of the above tests with different types of geosynthetics and soils. The main r...
Landfill Liners Stability Assessment using Interface Parameters
Landfill liner stability assessment using interface shear strength parameters have been a tedious testing and analysis process. The current testing procedures are based on ASTM testing guideline and basic fundamental engineering testing philosophies. Hence there is need for much ideal testing equipment which can perform the entire test series required for landfill liner parameter evaluations. The equipment are required to perform interface test between 1) soil and soil (CCLs), 2) geomembrane (HDPEs and PVC) and soil, 3) geosynthetic (GCLs) / compacted clay liners (CCLs) and soil, 4) geomembrane and geotextile, 5) geotextile and soil, 6) geotextile and geosynthetic (GCLs) / compacted clay liners (CCLs), 7) geomembrane and geosynthetic (GCLs) / compacted clay liners (CCLs). Having such high requirement and testing complexity for landfill liner system, this paper addresses the modification adopted to a large scale shear box in order to perform the above said interface tests. The modified large scale shear box was used to study interface performance of various combination of liners. Test data were compiled into a landfill model to study the stability performance of landfill liners under static and seismic loading to identify suitable liner configuration for both single and composite liner systems. The data from analysis results are compiled as quick reference guide for engineers involved in landfill liner design and maintenance. Details of laboratory test data and analysis results will be presented herewith. 4 TESTING APPARATUS Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.25 Case 2E-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.20 Case 2D-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.15 Case 2C-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.10 Case 2B-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.00 Case 2A-3 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.25 Case 2E-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.20 Case 2D-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.15 Case 2C-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.10 Case 2B-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.00 Case 2A-2 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.25 Case 2E-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.20 Case 2D-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.15 Case 2C-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.10 Case 2B-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.00 Case 2A-1 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.25 Case 1E-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.20 Case 1D-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.15 Case 1C-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.10 Case 1B-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.00 Case 1A-3 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.25 Case 1E-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.20 Case 1D-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.15 Case 1C-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.10 Case 1B-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.00 Case 1A-2 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.25 Case 1E-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.20 Case 1D-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.15 Case 1C-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.10 Case 1B-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.00 Case 1A-1 DESCRIPTION CASES Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.25 Case 2E-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.20 Case 2D-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.15 Case 2C-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.10 Case 2B-3 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.00 Case 2A-3 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.25 Case 2E-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.20 Case 2D-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.15 Case 2C-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.10 Case 2B-2 Slope height of 10m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.00 Case 2A-2 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.25 Case 2E-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.20 Case 2D-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.15 Case 2C-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.10 Case 2B-1 Slope height of 10m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.00 Case 2A-1 Slope height of 10m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.25 Case 1E-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.20 Case 1D-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.15 Case 1C-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.10 Case 1B-3 Slope height of 30m with 135m length with back slope angle of 1H:1V and seismic coefficient of 0.00 Case 1A-3 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.25 Case 1E-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.20 Case 1D-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.15 Case 1C-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.10 Case 1B-2 Slope height of 30m with 135m length with back slope angle of 2H:1V and seismic coefficient of 0.00 Case 1A-2 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.25 Case 1E-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.20 Case 1D-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.15 Case 1C-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.10 Case 1B-1 Slope height of 30m with 135m length with back slope angle of 3H:1V and seismic coefficient of 0.00 Case 1A-1 DESCRIPTION CASES
Performances of Landfill Liners under Dry and Wet Conditions
Geotechnical and Geological Engineering, 2011
This paper addresses the study conducted on the performance of landfill liner interface parameters. Interface shear strength parameters for various combinations of 9 different lining materials were studied and presented in this paper. This comprehensive testing program covers the interfaces between:
Interface shear strength of geosynthetics: Evaluation and analysis of inclined plane tests
Geotextiles and Geomembranes, 2009
The inclined plane test (IPT) is commonly performed to measure the interface shear strength between different materials as those used in cover systems of landfills. The test, when interpreted according to European test Standards provides the static interface friction angle, usually assumed for 50 mm displacement and denoted as f stat 50 . However, if interpreted considering the several phases of the sliding process, the test is capable of yielding more realistic information about the interface shear strength such as differentiating interfaces which exhibit the same value of f stat 50 but different behavior for displacement less than 50 mm. In this paper, the IPT is used to evaluate the interface shear strength of some materials usually present in cover liner systems of landfill. The results of the tests were analyzed for both, the static and the dynamic phases of the sliding and were interpreted based on the static initial friction angle, f 0 , and the limit friction angle, f lim . It is shown that depending on the sliding behavior of the interfaces, f stat 50 , which is usually adopted as the designing parameter in stability analysis, can be larger than f 0 and f lim .