The stability of landfills and leach pads is becoming more important with each new project failure and the increasingly difficult terrain of some sites. Shear strength of geosynthetic interfaces is one of the primary, and more contentious, variables used in stability analysis. The continued growth of the geosynthetics industry has led to a constant influx of professionals working in waste facility design and slope stability evaluation for the first time. These engineers, together with geomembrane and geosynthetic clay liner (GCL) manufacturers, have long complained of the difficulty in achieving good, reliable interface strength parameters.

The standard test method for the evaluation of friction between geosynthetics and geosynthetics, or geosynthetics and soil, is ASTM D 5321, large scale direct shear test for geosynthetics, and ASTM D6243 for GCLs. While these tests are simple in concept, the generated test results are significantly affected by the test parameters defined and the procedures used. As a result, understanding the specification of interface friction testing and how to interpret and use generated test results has become a crucial part of an engineer’s job. In fact, the cost for not understanding ASTM D 5321 and D6243 tests and test data can be enormous. Unfortunately, the waste industry has several examples of this cost.

This course had been specifically targeted to those persons who have a need to understand and specify interface friction/direct shear tests and use generated results in subsequent design. These persons include:

• Design/Certifying Engineers
• Construction/Quality Assurance Project Managers
• Manufacturers
• Installers
• Third-Party Inspectors
• Regulators

This course will be presented in two parts, each complementing the other to provide maximum benefit. The first will focus on the designer’s use of interface strength including sources of interface strength, peak vs residual strength, normal stress and failure envelopes, friction angle, adhesion and slope stability calculations. Included will be detailed forensic analysis of several slope failures.