Shear Strength Testing for Geotechnical Structures

Rahsn Witt

As geotechnical engineers, we often poke our finger into soil or hit rocks with a hammer to provide information used to select material properties required for design. The observations made while visiting the site to use the finger or hammer provide valuable additional information about the site, including the setting, materials and geometry. In some cases the inspection and finger are sufficient in other cases, a combination of approaches, including laboratory testing should be undertaken to build confidence in the material properties adopted in our designs.

As a designer the more information we have about our problem, including the material properties, the more efficiently and safely we can design our structures. Geotechnical engineers have a good practiced of providing detailed specifications for placement of fill and although there is generally good control on fill placement there is often no specification for the shear strength limits or shear strength testing frequency. This paper provides some results of shear strength testing of fill material derived from sandstone tunnel spoil used for temporary retaining structures and working platforms on a recent infrastructure project. It has been portrayed that the extent of testing should be linked to the sensitivity to material properties, the complexity, size and cost of the structure being designed.

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