This article presents results of the numerical analysis of the interaction between heavy caterpillar tracks system and subsoil. The main goal of the article is to present an algorithm to design working platforms - temporary structures enabling the work of heavy construction equipment on weak subsoils. A semi-analytical method is based on the results of the numerical analysis performed with use of the finite element method (FE software ZSoil.PC [12]). The calculations were carried out for the piling rig machine - Bauer BH20H (BT60). Three ground models were adopted: Model 1: one layer - weak cohesive soil (clay); Model 2: two layers: weak cohesive soil (clay) and cohesionless working platform (medium sand); Model 3: one layer: strong cohesionless subsoil (medium sand). The following problems were solved: I) entry of the machine on the ground with various geotechnical parameters under each caterpillar tracks II) detection of the maximum permissible angle of ground slope.

In this paper, the authors present an extension of the scope of the previously conducted research to the full three-dimensional computer simulation (using the finite element method), which takes into account the interaction between: heavy caterpillar tracks system – working platform – weak subsoil. The article presents a computer model considering two caterpillars, resting on elastic-plastic sub-soil, with standard Mohr-Coulomb yield conditions, allowing for computer simulation of the behavior of the system up to achievement of ultimate limit state. The results of the above model are treated as the reference for a simplified Analytical Models of estimating the limit state, which might be used in design procedures. In turn, these Analytical Models are enhancements of previously presented one. The most important results concluding form the Analytical Model are simple interaction formulas, in the space of moments acting on the machine-subsoil system, limiting a domain of safety in given soil conditions.