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In this study, a modification of resonant column/torsional shearing (RC/TS) apparatus was proposed to perform a qualitative analysis of a noncohesive soil specimen vibration during RC tests. An additional multipoint displacement detection system was installed in the RC/TS WF8500 device. In the new measuring system, 48 mini-magnets are attached to the side surface of a cylindrical soil specimen, creating a regular grid of measuring points. Around 48 Hall sensors (Honeywell SS495A1) are used to measure changes in the magnetic field strength due to the movement of the corresponding magnets on the surface of the specimen subjected to dynamic torque. The Hall sensor generates an analog signal that is proportional to the change in the magnetic field. The measurements are collected with a newly developed data acquisition system that consists of a set of analog-to-digital converters and a set of ARM (Advanced RISC (Reduced Instruction Sets Computing) Machine) microcontrollers. The measurement system is controlled with a dedicated software, ControlRec, developed by the authors. The measurements are taken synchronically with and independently from the standard RC test procedure. The new measuring technique allows to observe displacements of the 48 points on the specimens’ surface with over 4 times higher sampling rate than in the original measuring system. As a result, additional effects related to the mechanical wave propagation through soil specimen were observed (local disturbances in distribution of vibration amplitudes or significant displacements near the bottom end of the specimen, which is assumed to be fixed in the standard RC/TS results analysis), that could not be identified using the standard equipment of the device.

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.

The problem is a continuation of the research conducted at the University of Warmia and Mazury in Olsztyn, Institute of Building Engineering. It concerns the development of methods for the interpretation of the shear modulus measurements based on the tests conducted on a torsional shear (TS) apparatus. The issue has significant importance in determining the deformation parameters, essential to perform numerical simulations of the interaction between a geotechnical structure and the subsoil. The purpose of this study was to conduct a comparative analysis of the various methods of interpretation of research results based on direct and reverse analysis, as well as automated classification of the first cycle of the relationship between the shear stress and the shear strain components obtained from the TS test. The methodology for verification of the presented interpretative methods consists in carrying out a series of laboratory tests on non-cohesive and cohesive samples of different granulation and state parameters. The course of the research includes the following steps: elaboration of the granulometric composition of several samples of soil, determination of soil index properties and execution of TS tests. Various methods of interpretation of obtained results were taken into account, in addition to conducting a comparative analysis. The study used a non-standard interpretation approach consisting of analysing one-fourth of the hysteresis loop of the first load–unload cycle of the tested samples. The obtained results confirmed the hypothesis that it is possible to estimate the degradation value of the shear modulus based on a part of the TS test results carried out under quasi-monotonic load conditions. The proposed methods of interpreting test results have confirmed their high usefulness, which is devoid of the uncertainty associated with standardised resonant column/TS testing.

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.