Shear Strength of Single and Multi-layer Soil–Geosynthetic and Geosynthetic–Geosynthetic Interfaces Using Large Direct Shear Testing

Abstract

AbstractLandfill 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 materials tested. However, the peak and LD strengths were generally 9% and 24% lower, respectively, for single interface tests than for multi-layer interface tests across the range of normal stresses considered. This conservative estimate may be attributed to the rigid clamping of the geosynthetics, resulting in some tensile strains that reduce the peak and LD shear strengths. Moreover, it was observed in multi-layer interface tests that transfer of shear stresses within the system could have occurred, which could have led to higher overall peak and LD shear strengths. Higher displacements along the critical interface in single interface tests than in multi-layer interface tests may also contribute to this outcome. Overall, these findings have important implications for designing landfill liner systems and performing shear strength tests. Specifically, multi-layer interface tests provide a better simulation of field conditions and a more accurate representation of the shear strength characteristics of composite liner systems. However, performing multiple single interface tests may still be necessary to fully understand the shear strength of individual interfaces. Further research is needed to explore the implications of these findings for other materials and testing conditions.