The purpose of this paper is to report on the field tests for the formation of a single DR (dynamic replacement) column and its influence on the surrounding weak soil deposit. The influence of the column formation has been assessed with piezocone and dilatometer measurements, as well as by changes in the strength and deformation parameters obtained from the field tests. These measurements were carried out during and after the column formation and at varying distances from the column. The tests carried out have shown that soil close to the column became weaker during the column formation. As a result the soil stiffness and strength were found to increase over time. The weaker the soil was in natural state, the more significant the strengthening effect became. That indicates that changes occurring around a DR column are complex. The measurements suggest that the changes in soil structure have a tendency to be dependent on the distance from the column, elapsed time and the type and the initial condition of the soil.

The dynamic replacement method is used to strengthen the subgrade of objects, usually up to 5 to 6 m thick. After the improvement process, acceptance tests in the form of load testing are carried out. Interpretation of the test results can cause some difficulties. Dynamic replacement results in a situation where columns of different shapes, loaded with plates of diameters usually smaller than the head diameter and in the vicinity of adjacent columns, are subjected to load tests. In order to demonstrate the influence of these factors, a spatial model of soil strengthened by dynamic replacement, comprising four material zones, was calibrated on the basis of load testing. The following models were used in the analysis: linear-elastic, elastic–perfectly plastic (Coulomb–Mohr) and elastic–plastic with isotropic hardening (Modified Cam-Clay). This formed the basis for 105 numerical models, which took into account the actual shapes of the columns made at various spacings, subjected to load tests with plates of various diameters. The analyses of the settlements, calculated moduli and stress distribution in the loaded system showed how the results were significantly influenced by mentioned factors. This implies that the interpretation of the results of load tests should be based on advanced spatial numerical analyses, using appropriate constitutive models and including the considered factors.

Remediation and preparation for development is a crucial aspect of the valorization of post-mining areas. This study is focused on technologies devoted to the cement stabilization of post-industrial waste and petroleum contaminated soils. Two case studies are presented. Case 1 is based on the stabilization works of waste from a closed chemical plant in order to turn it into an engineered landfill. The results form the basis for numerical studies of slope stability. The shorter case 2 is based on the laboratory testing of a soil–cement composite with regard to petroleum contamination and the application of active carbon to neutralize it in the course of deep soil mixing. Both cases, due to the use of slag cement, are not considered to be sustainable (due to a relatively high carbon footprint), but they represent current geotechnical practice and form a reference for a wide range of applications. Both cases show the positive impact of stabilization by means of the addition of a hydraulic binder. The effect of soil improvement is measurable in terms of the stability factor of landfill slopes. The effect of active charcoal addition seems to be a valuable improvement to standard deep soil mixing technology in the case of contaminated soil. The presented results, despite their local importance related to the cases under scrutiny, have an important educational and scientific value for the energy sector, where contaminated sites need to be valorized.

Dynamic replacement (DR) is a ground improvement technique that has been used now for almost 50 years. During the formation of a DR column a crater is created which is then filled with a coarse material and compacted again. The length, diameter and shape of such a column cannot be observed directly, which makes the design and execution more troublesome. In the article presented are the dimensions and shapes of 18 columns from eight different test fields. They were formed by means of pounders of various masses (9 or 11.5 Mg) and dimensions (1.00 or 1.05 m in diameter, 1.8 or 2.0 m in height). Based on the observations and measurements, it was concluded that the shape and diameter of a DR column is influenced by the parameters of the soft soil that is supposed to be improved (its thickness, physical state and location in the profile), as well as by the diameter of the pounder. It was revealed that, as the length of the columns increased, the column shapes changed from: a cylinder, through a truncated cone, a barrel to an asymmetric barrel. The diameters of all of the columns were 1.4–2.8 times larger than the diameters of the used pounders and the largest values were noted along the depth of the weakest layer. The presented results may be useful to the profession. When the thickness of the weak soil, its type and state are known and the technological parameters are similar to the ones presented in this paper, it is possible to predict the shape and diameter of the columns depending on the diameter of the pounder.