Stability performance and interface shear strength of geocomposite drain/soil systems (original) (raw)
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Evaluation of Hydro-Mechanical Behaviour of Hydraulic Barriers of Landfill Covers
Proceedings of GeoShanghai 2018 International Conference: Geoenvironment and Geohazard, 2018
Bentonite amended local soils are used as hydraulic barriers (CB) in municipal solid waste landfills and for the disposal of low level radioactive waste stored containers. Excessive settlements can cause cracks in the CB which affect the strength and provide preferential flow paths to fluids compromising the sealing efficiency of the barrier. Thus, the integrity of CB with respect to their hydraulic conductivity and flexural strength is very important to prevent the environment hazards. In the present study, a series of hydraulic conductivity tests, direct tensile tests and centrifuge model tests were conducted on model barriers. The influence of waste settlement on the long term performance of the barriers was studied by conducting a series of centrifuge model tests. Digital Image Cross-Correlation technique was used in the present study for obtaining the tensile strain in the barrier during settlement. Since, clay is having low tensile strength and low tensile strain at failure, an attempt was made to improve its tensile strength by using polyester discrete geofibers. A custom designed direct tensile test setup was used to evaluate the tensile strength-strain characteristics of the unreinforced CB and fiber reinforced soil barriers (FB). A flexible wall permeameter was used in the present study for studying the influence of geofibers on the hydraulic conductivity of the barriers. From the present study, it was observed that for the type of fibers, fiber dosage and length and soil used in the present study, the tensile strain at failure was increased to a maximum of 2.5 times and hydraulic conductivity of the soil has not varied drastically and satisfied target hydraulic conductivity requirements for the hydraulic barriers of the landfills.
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...
The objective of this paper is to examine the influence of settlement rate and geogrid reinforcement on the deformation behaviour of soil barriers of landfill covers subjected to differential settlements. A series of centrifuge tests were performed on soil barriers at 40 gravities. Two different settlement rates were induced using motor-based differential settlement simulator designed for a high gravity environment. Centrifuge tests on a 1.2 m thick unreinforced soil barrier subjected to two different settlement rates without provision of any overburden pressure was found to experience identical deformation profiles and cracking pattern. A slight delay in the occurrence of crack initiation and an increase in the strain at crack initiation was noticed when the soil barrier was tested at slow settlement rate. An increase in the limiting distortion level from 0.044 to 0.069 was noticed when the unreinforced soil barrier was subjected to an overburden pressure equivalent to that of cover system. When the soil barrier was reinforced with a geogrid layer without any overburden pressure, the limiting distortion level was increased from 0.044 to 0.064. An increase in the maximum mobilized tensile load of model geogrid from 77 kN/m to 120 kN/m was observed with the provision of overburden pressureequivalent to that of cover system.
Dynamic Shear Degradation of Geosynthetic–Soil Interface in Waste Landfill Sites
Applied Sciences, 2017
Geosynthetics and soil particles inevitably come into contact, resulting in a geosynthetic-soil interface. The discontinuity of the materials at the interface causes an intricate shear response, especially under dynamic loads. In the present study, the effects of chemical aggressors of the leachate from a waste landfill site on the cyclic shear behaviors of a geosynthetic-soil interface were investigated. The MultiPurpose Interface Apparatus (M-PIA) that can simulate cyclic simple shear conditions was utilized, and 72 sets of cyclic simple shear tests were conducted. The Disturbed State Concept (DSC) was employed to quantitatively estimate the shear stress degradation. As a result, new disturbance functions and parameters that represent the characteristics of the dynamic shear degradation at the interface were evaluated. Additionally, a numerical back-prediction was performed to verify the accuracy and applicability of the DSC parameters. Numerical interpolation procedures were suggested and enabled to reproduce the degradation successfully. Consequently, a general methodology was established to estimate the cyclic shear stress degradation of the geosynthetic-soil interface in consideration of chemical effects.
Influence of geomembrane on the deformation behaviour of clay-based landfill covers
Geotextiles and Geomembranes, 2012
Clay-based landfill covers often have a geomembrane (GM) layer sandwiching between the clay barrier and the cover soil. The knowledge pertaining to the deformation behaviour of a clay barrier along with geomembrane subjected to differential settlements is very limited. Hence, the main objective of this paper is to examine the influence of GM on the integrity of clay-based landfill covers subjected to differential settlements in a geotechnical centrifuge. First, scaling considerations required for modelling geomembrane in a centrifuge are presented. A series of centrifuge tests were performed at 40 gravities using a 4.5 m radius beam centrifuge having a capacity of 2500 g-kN available at IIT Bombay on model clay-based landfill covers with and without GM. By maintaining type moist-compacted conditions of the clay barrier as constant, the thickness of the clay barrier was varied as 0.6 m and 1 m. The performance of the clay barrier with and without GM was monitored by measuring water breakthrough at the onset of differential settlements. The analysis and interpretation of centrifuge test results reveal that with the provision of a GM and an overburden pressure equivalent to that of a landfill cover, the sealing efficiency of the cover system was found to be maintained even after the formation of full-depth cracks within 0.6 m and 1 m thick clay barriers subjected to a maximum distortion level of 0.125. This observed behaviour is attributed to the downward thrust exerted by the deformed geomembrane at the zone of maximum curvature which hinders the infiltration of water through cracks. This indicates the significant influence of GM in maintaining the sealing efficiency of a landfill cover system.
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...
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.
GeoCongress 2012, 2012
The objective of this paper is to examine the deformation behavior and water tightness of clay-based composite cover of landfills subjected to differential settlements using a centrifuge modeling technique. A short series of centrifuge tests were performed at 40 gravities on model composite cover system formed using a model clay barrier of 15mm (0.6m) thickness, geomembrane and overburden equivalent to that of landfill covers. The effect of presence of overlaps within the geomembrane layers at the zone of maximum curvature was also investigated. Centrifuge model test results on cover system formed with a 15mm (0.6m) thick clay barrier experienced water breakthrough once limiting distortion level is equal to 0.056. In comparison, a composite cover system formed with a 15mm (0.6m) thick clay barrier and a geomembrane was found to sustain large distortions without any water breakthrough even after subjecting to a maximum distortion level of 0.125. However, with the presence of overlaps at the zone of maximum curvature, the sealing efficiency of the composite cover with 15mm (0.6m) thick clay barrier was observed to decrease and limiting distortion level was 0.10. An attempt was also made to model the deformation behavior of barriers with and without geomembrane by finite element analysis using Plaxis 2D software.
Clay geosynthetic barriers performance in landfill covers
Clay geosynthetic barriers (GBR-Cs) used in landfill covers must ensure lining on the long term. The primary mode of ageing of bentonite GBR-Cs in covers is the coupling of cation exchange and hydrationdesiccation cycles. The objective of this paper is to synthesize the optimal conditions to prevent a loss of performance of GBR-Cs in covers with time, based on a literature review. Various parameters will be discussed. The literature review will put in light the lack of consistent information from study to study. This enforces the need for a list of information to collect in future excavations. Such a list is proposed in the third section of this paper followed by the presentation of results from recent excavations performed by the first author. Formatted Formatted Formatted
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)/...