Constitutive Modelling of Multiporous Lumpy Soils

The deposition of excavated natural soils, e.g. in open pit mines or during land reclamation, produces in general lumpy soils with multimodal pore sizes. The mechanical behaviour of such soils is determined by interaction between the firm to stiff lumps and the soft to liquid soil material in the macrovoids between the lumps. The initial skeleton composed of lumps resembles a coarse grained soil. However, contrary to mineral grains, the macrograins (lumps) are not incompressible and time-independent. Due to rising overburden during the subsequent deposition of the excavated soil, a time-dependent deformation of the lumps takes place, being accompanied by a softening of the lumps' surface. The space between the lumps, originally occupied by air, becomes gradually filled with that soft material. A constitutive description of the lumpy soils should take into account all the mentioned effects. In this paper, main ideas and fundamentals for the constitutive modelling of the relevant phases of lumpy soils are outlined. With help of a homogenization method, a material model suitable for practical applications can be obtained.