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Comparison of shear strength properties of textured polyethylene geomembrane interfaces in landfill liner systems
The interface shear strength between geomembranes and geosynthetics is a critical factor governing the stability of slopes that incorporate geosynthetics. In order to better characterise the shear properties of geomembranes, a wide-range of shear strength friction measurements were conducted. This dissertation presents the results of a study that examined interface shear strength parameters of textured high density polyethylene geomembranes (HDPE) and textured low linear density polyethylene (LLDPE) geomembranes sheared against different geosynthetics; geotextiles, geogrid and geosynthetic clay liners (GCLs), typically used in South African landfill base liners and capping systems. Tests were performed using a modified 305 x 305 mm x 100 mm large direct shear box over a range of normal pressures of 25, 50, 100, 150, 200 and 300 kPa. Shear rates of 0.1 mm/min and 1 mm/min were used for geomembrane/ GCL and geomembrane/ geosynthetic interfaces respectively. Results indicated that LLDPE and HDPE geomembranes sheared against various geosynthetic combinations produced different friction characteristics which resulted in varying performance patterns. HDPE geomembrane surfaces mainly experienced conventional linear failure envelopes when sheared with different geosynthetics. However, LLDPE geomembrane interfaces showed that the linear failure envelopes did not always give the best representation of the shear stress and normal stress relationship for sheared interfaces. These geomembrane shear strength envelopes could be described as linear until a critical confining stress in the range of 100 kPa to 150 kPa was attained, therefore making the failure envelopes bilinear. A comparison of the linear and bilinear failure envelopes showed that a bilinear failure envelope was a more appropriate approximation over large normal stress ranges. A bilinear relationship resulted in higher interface friction angles and low apparent adhesion parameters being achieved at normal stresses less than 100 or 150 kPa. While low interface friction angles and large adhesion values were produced above the critical confining pressure. Although HDPE geomembrane interfaces indicated larger stiffness and rigidity at early shear, it was observed that LLDPE geomembrane/ geosynthetic interfaces presented larger factor of safety values when compared to HDPE geomembranes sheared against majority of the geosynthetics. These results were produced when friction parameters generated from this study were applied to practical design examples of landfill base liner and capping systems. From these observations several practical recommendations were generated to assist professionals to choose suitable materials during design.
Comparison of shear strength properties of textured polyethylene geomembrane interfaces in landfill liner systems
The interface shear strength between geomembranes and geosynthetics is a critical factor governing the stability of slopes that incorporate geosynthetics. In order to better characterise the shear properties of geomembranes, a wide-range of shear strength friction measurements were conducted. This dissertation presents the results of a study that examined interface shear strength parameters of textured high density polyethylene geomembranes (HDPE) and textured low linear density polyethylene (LLDPE) geomembranes sheared against different geosynthetics; geotextiles, geogrid and geosynthetic clay liners (GCLs), typically used in South African landfill base liners and capping systems. Tests were performed using a modified 305 x 305 mm x 100 mm large direct shear box over a range of normal pressures of 25, 50, 100, 150, 200 and 300 kPa. Shear rates of 0.1 mm/min and 1 mm/min were used for geomembrane/ GCL and geomembrane/ geosynthetic interfaces respectively. Results indicated that LLDPE and HDPE geomembranes sheared against various geosynthetic combinations produced different friction characteristics which resulted in varying performance patterns. HDPE geomembrane surfaces mainly experienced conventional linear failure envelopes when sheared with different geosynthetics. However, LLDPE geomembrane interfaces showed that the linear failure envelopes did not always give the best representation of the shear stress and normal stress relationship for sheared interfaces. These geomembrane shear strength envelopes could be described as linear until a critical confining stress in the range of 100 kPa to 150 kPa was attained, therefore making the failure envelopes bilinear. A comparison of the linear and bilinear failure envelopes showed that a bilinear failure envelope was a more appropriate approximation over large normal stress ranges. A bilinear relationship resulted in higher interface friction angles and low apparent adhesion parameters being achieved at normal stresses less than 100 or 150 kPa. While low interface friction angles and large adhesion values were produced above the critical confining pressure. Although HDPE geomembrane interfaces indicated larger stiffness and rigidity at early shear, it was observed that LLDPE geomembrane/ geosynthetic interfaces presented larger factor of safety values when compared to HDPE geomembranes sheared against majority of the geosynthetics. These results were produced when friction parameters generated from this study were applied to practical design examples of landfill base liner and capping systems. From these observations several practical recommendations were generated to assist professionals to choose suitable materials during design.
Comparison of shear strength properties of textured polyethylene geomembrane interfaces in landfill liner systems
2019-01-01
Theses
Electronic Resource
English
DDC:
690
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