N Dixon, W Blumel, C Stoewahse, P Kamugisha and DRV Jones. This paper was first published in GE’s March 2002 edition.
Interface shear strength parameters are required for use in design calculations to assess the stability of a wide range of geotechnical structures incorporating geosynthetics. These include the design of landfill barriers and reinforced earth structures.
Limit equilibrium calculations can be carried out using a global safety factor (traditional approach) and using partial factors on both resisting and disturbing forces (limit state approach defined in Eurocode 7, 1994).
In the global safety factor approach it is necessary to obtain conservatively chosen mean values of shear strength. The Eurocode 7 approach is to obtain characteristic values of shear strength. In both cases a limited number of site-specific laboratory tests is usually supplemented by subjective experience. For practical purposes it can be assumed that characteristic value (EC7) and the conservatively chosen mean value (traditional) are equivalent (Schneider, 1997), and therefore the recommendations in this paper can be applied to both design approaches.
This paper provides guidance on obtaining characteristic values of the interface shear strength parameters (apparent adhesion, n„and friction angle, 5k) for use in design calculations. A companion paper (Stoewahse et al 2002 - Ground Engineering February) discussed factors influencing the measurement of interface shear strength behaviour.