Influence of selected technological parameters on dynamic replacement column formation – results of laboratory model tests

The paper presents results of the research on the influence of selected technological parameters on dynamic replacement columns formation. The analysis concerned: the depth of the initial crater H_cr, the volume of its filling V_cr, and the grain size of the backf used. It was carried out on a testing stand that allowed the observation and documentation of the particle driving process. The soft soil layer was simulated with a hydrogel, while the bearing layer was made of medium sand. The columns were formed in the initial craters, with a depth of 0.4, 0.6 or 0.8 of the thickness of the soft layer, and backfilled up to 50, 75 or 100% of the volume. The investigation of the optimal crater and backfill volume was carried out using medium gravel (2–16 mm). The influence of the grain size of the backfill material was studied at the optimal H_cr and V_cr – medium sand (0.063–2 mm) and medium gravel (2–32 mm) were used at this stage. The displacements of backfill material grains and the shapes of the columns were analysed using GOM and Cad software. The optimal solution was to construct the columns in the shallow crater (H_cr /H_s = 0.4) and to backfill it with gravel 2–16 mm up to 50% of the volume – under these conditions, end-bearing columns were formed with the diameter increasing with depth. In order to improve the shape of the column, in the final phase of the DR process, V_cr shall be increased up to 100%.