Design and development of a large shear box for testing working platform material

On large construction projects where deep foundations are to be installed, a working platform is placed across the entire site. This is comprised of a layer of aggregate (often crushed construction waste) usually with a particle size ranging from 120 mm downwards. Deep foundations are installed using heavy and tall drilling rigs and the working platform is thus safety critical to reduce the risk of machinery sinking and/or toppling which would lead to accidents and often serious injury to workers. Currently available design guidance is felt to result in conservative designs and there are many benefits to be gained from a greater understanding of the behaviour of working platform material. The design of these platforms is primarily governed by the angle of friction of the platform material. The measurement of friction angle for geomaterials that have large particle sizes is problematic (due to reasons of scale) and is often addressed by scaling down the material's grading curve prior to testing in small to medium size direct shear apparatus. The work presented here details the design of and the rationale for a large scale direct shear apparatus suitable for testing geomaterials with particle size distributions of the type that would be utilised in working platforms.