Using the 'step zero' approach to design a centrifuge modelling program

The design of a centrifuge modeling program for a clay bed with an interbedded sand layer is outlined following the 'step zero' approach. A modified sand overlying clay model was used incorporating the top clay as an effective surcharge. The tests aimed to investigate punch through failure, and the subsequent stabilization of bearing capacity. To this behavior within the limited depth of the test box a certain vertical free boundary distance (F BD ) is required, which controls the required ratio of soil sample depth to foundation size. In assessing this requirement based on existing calculation methods for punch through, the following four factors were found to be crucial: (i) intercept strength of clay at sand-clay interface; (ii) soil strength gradient of the clay layer; (iii) relative density of sand; and (iv) relative sand layer thickness to foundation diameter. As a result of planning and implementing a 'step zero' approach, the majority of the tests successfully captured the peak resistance and the depth of the punch-through event. The planning approach demonstrated here serves as an example for future centrifuge test design in similar scenarios. © 2010 Taylor & Francis Group, London.