In this study the effect of using a biopolymer soil stabilizer on soil stiffness characteristics was investigated. Chitosan is a bio-waste material that is obtained by chemical treatment of chitin (a chemical component of fungi or crustaceans’ shells). Using chitosan solution as a soil stabilizer is based on the assumption that the biopolymer forms temporary bonds with soil particles. What is important is that these bonds are biodegradable, so the product does not leave any harmful waste and has high eco-compatibility. The biopolymer itself is a by-product of many industrial chemical processes, so its application is compliant with the goals of sustainable geotechnical engineering. The effect of chitosan on soil shear strength, permeability or surface erosion has already been investigated in several different studies. In this study specimens of low-cohesive soil stabilized with two different chitosan solutions were subject to cyclic loading (torsional shearing test) and dynamic loading (resonant column) to obtain soil shear modulus G as a function of strain values. It has been shown that chitosan solution added to medium-grained materials improves their shear modulus G substantially (up to 3 times) even for relatively low chitosan concentration solutions (1.5 g of chitosan per 1 kg of dry silica sand). The results obtained in this study and the known chitosan properties suggest that chitosan solutions can be a very effective and eco-friendly short-term stabilizer for temporary geotechnical structures, e.g., working platforms.

The paper presents the results of laboratory tests, that verify the correlation between the grain-size characteristics of non-cohesive soils and the value of the dynamic shear modulus. The problem is a continuation of the research performed at the Institute of Soil Mechanics and Rock Mechanics in Karlsruhe, by T. Wichtmann and T. Triantafyllidis, who derived the extension of the applicability of the Hardin’s equation describing the explicite dependence between the grain size distribution of sands and the values of dynamic shear modulus. For this purpose, piezo-ceramic bender elements generating elastic waves were used to investigate the mechanical properties of the specimens with artificially generated particle distribution. The obtained results confirmed the hypothesis that grain size distribution of non-cohesive soils has a significant influence on the dynamic shear modulus, but at the same time they have shown that obtaining unambiguous results from bender element tests is a difficult task in practical applications.

The paper presents a selected aspect of the determining the initial soil shear modulus value on the research example in resonant column – torsional shear apparatus (RC / TS). There are presented the significance of the initial value of shear modulus in design of offshore wind power plant foundations and the importance of its variability in the function of cyclical shear strains of soil related to the impact of sea and atmosphere on the designed structures. Based on the conducted analyses, a new methodology for interpreting the TS test results of soil has been proposed. It allows estimating the values of the shear modulus in the full range of shear strains occurring in issues closely related to the design and construction work of offshore wind power plant foundations.

With the accelerating progression of global climate change, switching to renewable energy sources is inevitable. Wind energy is a fast-growing branch of this industry, and according to the 2021 Global Wind Report, this trend must continue in order to limit the increase in global average temperature. While onshore wind turbines still dominate and account for most recent growth, offshore wind turbines are becoming a promising alternative for geographical, power density-related or even aesthetic reasons. Offshore wind turbines are subjected to more complex loading conditions and proper foundation design is very challenging, however, this is crucial for ensuring and maintaining the structure’s reliability. Soil dynamic tests are one of the bases for wind turbine foundation design. Technical regulations in many countries require such tests to be carried out in a Resonant Column (RC). In this study, a modification of the RC sensors and data acquisition system was introduced in order to conduct in-depth analysis of vibrating soil specimens. The new set of sensors contained five additional accelerometers (Analog Devices ADXL345) attached to the surface of a soil specimen that was subjected to dynamic loading. These accelerometers sent the data to a new data acquisition system, an ARM microcontroller with software developed by authors. The software was able to process test results synchronously with the original software of the RC device. Additionally, the load control system was supplemented with a current pulse generator, which makes it possible to observe the propagation of high-frequency mechanical waves in the tested materials. The modified dynamic testing equipment allowed for the measuring of accelerations and displacements at specific selected points located along the height of the sample, with sampling frequency more than three times higher than that offered by the sensors originally built into the RC device. As a result, some additional dynamic phenomena (i.e., disturbances in the uniformity of vibrations of non-cohesive materials, specimen–device contact imperfections) were observed in the tested soil specimens which remained undetected in standard RC test.

Accurate modelling of the phenomena occurring in loaded soil materials is the primary source of development of the current normative regulations as well as smarter and more efficient engineering practice. The aim of this research is to develop a more accurate description of the complex nature of the soil material and thus a more accurate evaluation of the subsoil-construction interaction in the whole range of stress, not only in chosen limit states. The proper description of the behaviour of soil in the range of small strain is an extremely important element to forecast displacements of construction interacting with subsoil. Due to this fact, it has a huge influence on the quality of mapping the actual internal forces in the whole structure - including the foundation. Stiffness moduli for small strains are actually recognized as one of the most important properties of the soil. RC/TS is the reference apparatus in which they are determined. A technique based on the analytical solutions was used to calculate the dynamic shear modulus, dynamic modulus of elasticity and the damping coefficient of soils and rocks. In theory, the movement of the tested soil particles resulting from the propagation of elastic waves is non-destructive. Despite the apparent differences in the behaviour of soil material under dynamic loads with a significant frequency (approx. 60- 160Hz - RC test) and quasi-static loads, characterized by very low frequency amplitude (below 10Hz, in practice 0.1Hz below - TS test), small strain conditions are modelled numerically using a combination of linear and non-linear laws of elasticity. The main drawback of standard RC/TS research methodology is the assumption that soil material is subject only to viscoelastic strain. This assumption is manifested, among others in the interpretation of the damping coefficient during TS test, which is defined as the proportion of the energy dissipated by the material during the cyclic torsional shearing to the potential energy accumulated in the material during elastic deformations. However, observations confirm the hypothesis that the behaviour of the soil, even in the range of small strains, should be considered as elasto-plastic - including the generation of a plastic, irreversible deformation. The research method involves executing multiple (repeated) torsional shear tests on natural and artificial (repeatable) structure samples of soil. Samples were subjected to varying conditions of the amplitude and frequency of cyclic load. Using modified procedure of registration test results allows the observation of changes in viscoelastic strain of material and measurement of permanent deformation after the completion of the torque impact. Multiple repetitions of tests on samples of the natural and artificial structure allows to identify the cause of any differences that may arise in the individual reactions of the material (phase elastic, viscous, plastic).