Numerical analyses of the 2D bearing capacity of block-in-matrix soils (bimsoils) under shallow foundations

Abstract

Bimsoils are mixtures of large geotechnically significant competent blocks embedded in a weaker soil matrix. Conventional design approaches usually account for the matrix strength characteristics, while empirical approaches use the volumetric block proportion (VBP) to modify matrix strength considering the presence of blocks. This article outlines a numerical approach to study the 2D bearing capacity of bimsoils, considering block sizes between 5% and 75% of the footing width, areal block proportions up to 70% of the problem domain as well as welded and unwelded block-matrix-contacts. Sampling algorithms to produce monodisperse and polydisperse block distributions were developed. Bimsoil samples were investigated using finite-element limit analysis. Results were presented in terms of a dimensionless factor Φγ/c. The results showed that not only VBP but also the size of the blocks had a major influence on the bearing capacity. An explanation for this observation was supported by the shape of the failure surface, whose complexity significantly increased with increasing block sizes and block proportions. Moreover, larger shear strengths found in the block-matrix-interface due to welded block-matrix-contacts led to larger bearing capacities. This effect was more dominant in a frictional rather than a cohesive soil matrix.