Calibration of the Numerical Model of a Dynamic Replacement Column Formed Under Laboratory Conditions

During dynamic replacement, the contractor has no direct control over the length of the column and its diameter. Therefore, field trial tests performed at the beginning of the work site are extremely important. An alternative may be numerical analyses that permit modelling of column driving with variable technological parameters. The approach of combining meshed methods (FEM) and meshless methods (SPH) using the ANSYS LS-Dyna program with model calibration based on their own laboratory tests was used. A two-dimensional (2D) model was proposed in an axisymmetric state of deformation for calculations. The top layer was divided into two parts: in place of the examined largest displacements, the substrate is modelled by SPH elements and in the remaining part by FEM elements. The load-bearing layer and the pounder were modelled with FEM elements, while the backfill material was modelled with SPH elements. The analysis modelled the drop of pounder, its extraction, insertion of the backfill, and then the drop of free pounder into the crater. For the modelling an elastic-perfectly plastic model with the Mohr-Coulomb failure criterion (for soils) and rigid model (for pounder) were used. The parameters of the adopted models were selected on the basis of laboratory tests and the literature. Modelling of dynamic replacement using an elastic-perfectly plastic model with the Mohr-Coulomb failure criterion allowed for a good reflection of the initial stage of column driving associated mainly with soil failure and greater discrepancies with laboratory results for some of the remaining stages related to soil compaction.