Calibration of the dynamic replacement column forming model with the softening of the soil and columns stiffness increase

Abstract

During the formation of dynamic replacement columns, the contractor has no direct control over the column length and diameter. Therefore, field trial tests performed at the beginning of the project are of crucial importance. An alternative approach involves numerical analyses that enable simulation of the column driving process under variable technological parameters. The preliminary calibration of the model was carried out by the authors by combining meshed (finite element method) and meshless (smoothed-particle hydrodynamics) methods in ANSYS LS-DYNA, based on their own laboratory tests, and demonstrated the model’s suitability for dynamic replacement modelling. Due to difficulties in reproducing the complete physical process, several modifications were required, including expanding the SPH-modelled domain, introducing subsoil softening associated with column penetration, and increasing the stiffness of the driven backfill. These implemented modifications made it possible to capture the entire column-forming process and the penetration of aggregate into the load-bearing layer, yielding a semicircular pattern of aggregate propagation and producing a lower column geometry consistent with that observed in laboratory tests. The proposed models reproduce lateral deformations in the immediate vicinity of the column reasonably well, particularly at distances corresponding to 0.7–0.9 of the maximum column diameter, whereas at greater distances, the predicted deformations are significantly overestimated. Further model refinements are both feasible and necessary, including adjustments to the representation of backfill volume and the incorporation of more advanced constitutive models.