Stochastic 3D modelling of discrete sediment bodies for geotechnical applications

In the course of engineering geological ground characterizations, internal structures of sediments are often simplified to continuous units and structures like lenses are drawn in cross sections based on geologists’ experience. Seeing this as oversimplifications, we propose discrete sediment body (DSB) modelling which is a computational workflow that permits generation of 3D meshes of sediment bodies. DSB modelling can be used to stochastically model highly detailed sedimentary underground structures, based on geometrical assumptions (e.g. size and orientation of lenses) that can be derived from engineering geological investigations. From a geological point of view, the framework is suited to model underground conditions where one would describe the occurrence of chaotic lens-shaped sediments. The modelling process follows a pipeline, where first estimations about the distribution and geometries of the sediment bodies are made. To get non-intersecting meshes as a final product, surrogate point clouds are generated that follow the initial geometrical estimations, which are then clustered, and finally alpha shape based meshes are generated around the clusters. Resulting 3D sediment bodies enable easy generation of consistent 2D geological cross sections and can be used as a basis for further analyses. The paper is finished with a case study where a finite element stability analysis is done for a slope excavation with underground conditions featuring clayey silt lenses in a matrix of gravelly sand. It can be shown that the lenses substantially influence the ground behavior in comparison to a classical approach with continuous units.