Collapse surface characteristics of clayey sands

It has been shown that a certain collapse surface may be defined for loose sands in three-dimensional space, in which the sample sand experiences collapse and instability, leading to unsteady and strain-softening behaviour. The unsteady state due to the collapse surface may lead to such phenomena in the sand as liquefaction and flow behaviour during undrained loading. Investigating the existence of the collapse surface in Firoozkooh 161 sand and its different clay mixtures with various plasticities, the present study aims to carry out an in-depth investigation of the effects of clay percentage and plasticity on sand critical-state or steady-state behaviours. The results obtained indicate that collapse surface characteristics depend largely on the fine percentage and the plasticity. Interesting findings are also reported in this paper on the effects of fine sand percentage and plasticity on the behavioural characteristics and liquefaction potential of clayey sands.