The surface bearing capacity of a strong granular layer on weaker sand

Stronger granular layers are often placed as working platforms over weaker sand subgrade. The design of a working platform involves the calculation of a two-layer bearing capacity under rectangular loading. Existing design methods are either overly simplified, based on infinitely long strip loads, validated by a small number of small-scale 1g model tests or rely on numerous or empirically derived charts that are difficult to use or implement into design software. In this paper a new and highly practical design method is proposed where bearing capacity is determined simply from the shear strengths and unit weights of the two soil layers. It was derived from extensive FEA and FELA parametric studies in both plane strain and axisymmetric geometries and validated against published physical model tests, other FELA analyses and existing design methods. It can be applied to all rectangular shape ratios with dry and saturated layers.