Interface shear strength variability and its use in reliability-based landfill stability analysis (original) (raw)
E3S Web of Conferences
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...
International Journal of Engineering Sciences & Research Technology, 2014
Now a day’s failure of modern landfills by slippage of lining materials is common. The majority of failures are controlled by slippage at interfaces between lining components. Information and variability of interface shear strength is required to carry out both limit equilibrium stability analysis using characteristic shear strengths and probability of failure analysis. 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. The implications of variable shear strength are examined though probability of failure analysis of two common design cases: veneer and waste body slippage. 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 of probability failure (Pf) values
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.
The Evolution of Geotech - 25 Years of Innovation, 2021
Geomembrane asperities are surface protrusions which distinguish smooth ge omembranes from textured geomembranes. Asperities possess geometrical features such as height and concentration and are hypothesised to develop high interface shear strength, resist sliding and increases stability. To date, many textured-geomembranes with different asperity geometries have been manufactured and used in landfill linings together with geosynthetics like geotextiles. Previous studies have considered the effects of asperity geometries to geomem brane/geotextile interface shear characteristics. However, limited studies have considered the effects of asperity height and concentration on the landfill side-slope liner factor of safety (FoS) using the geomem-brane/geotextile critical interface as the point of reference. Thus, this study was aimed at investigating the influence of asperity geometries on liner stability. This study utilized experimental results from direct shear test (i.e. friction angle and adhesion) and performed probabilistic stability analysis using SLIDE2. Available results indicated that FoS increased as both asperity concentration and height increased. However, asperity-height increased beyond 1.2 mm mobilized FoS reduction. Therefore, obtaining an optimised liner stability factor is hinged on selecting the appropriate geomembrane asperity geometry at the critical geomembrane/geotextile interface.
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...
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
Back-Analyses of Landfill Slope Failures
2008
This paper investigates the shear strength of municipal solid waste (MSW) using back analyses of failed waste slopes. Shear strength of MSW is a function of many factors such as waste type, composition, compaction, daily cover, moisture conditions, age, decomposition, overburden pressure, etc. These factors together with non-standardized sampling methods, insufficient sample size to be representative of in-situ conditions, and limited shear displacement or axial strain imposed during the shear tests affect the test results and have created considerable scatter in reported test results. This scatter led the authors to pursue the back-analysis of failed waste slopes as a better means for estimating the shear strength of MSW. The back-analysis of failed waste slopes in the Gnojna Grora landfill in Poland, Istanbul Landfill in Turkey, Hiriya Landfill in Israel, and Payatas Landfill in Philippines are presented in this paper. Each of the landfill slope failures is reviewed and the result...
Waste/Lining System Interaction: Implications for Landfill Design and Performance
Despite the relative maturity of landfill design practice, worldwide there are still significant numbers of large scale failures of waste bodies, often incorporating the lining system. In addition, there is growing evidence that post waste placement deformations in the lining system are leading to loss of function (i.e. discontinuous drainage layers, loss on protection and leaking liners). Best practice has established that both stability and integrity of the lining system must be assessed during the design process, and specifically that interaction between the waste body and lining system should be considered both in the short-term (i.e. during construction) and long-term (i.e. following waste degradation). The paper introduces available analysis approaches, reviews knowledge of waste behaviour required for such analyses and provides guidance on the mechanisms to consider. The need for field monitoring to validate numerical models is established as is the need for extensive measurements of waste mechanics properties linked to a standard classification system to aid comparison and use. The benefits of using probability of failure analysis to incorporate material and test variability in design are highlighted.
Influence of the Design on Slope Stability in Solid Waste Landfills
Earth sciences, 2013
This paper presents, firstly, the influence of the geometry of a slope in the safety factor (SF). In order to do this, the SF is compared among three types of slopes: with berms every 7 m high and a dam at the toe, without berms and with a dam at the toe, and without berms nor dams. It was observed that, for the same inclination, the berms do not significantly influence the stability. However, the construction of an earth dam at the base increases safety, especially with little height and slope in waste with poor mechanical properties. On the other hand, a set of diagrams to learn, quickly and easily, the safety factor of a landfill slope has been developed. Thus, this set of diagrams allows calculations from the SF height (from 17 to 80 m) and slope inclination (from 45° to 14°) with values of effective cohesion of the waste (C'o) from 1 to 3 t/m 2 and effective friction angle (Φ') of 10° to 25°.