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Conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axisymmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone-like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axisymmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled three-dimensional finite-element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample's end-restraints (rough or smooth). The effects are quantified in terms of the sample's overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce ‘bending’ in the sample.

The effect of curing time, content of grout solution and concentration of urea, calcium chloride and urease enzyme on the process of enzymatic calcium carbonate precipitation was analysed. Initially, the process was studied in test-tube experiments by evaluating the amount of calcium carbonate precipitated using X-ray diffraction tests. The method was then applied to stabilise a sandy soil to examine the strengthening effect using unconfined compressive strength tests, X-ray diffraction and scanning electron microscopy. The results showed the effectiveness of the method for improving the mechanical properties of a sandy soil. The soil strength and stiffness increased with increases in content of the grout solution and curing time, while an increase in the concentration of urease and urea–calcium chloride only had a positive effect for lower concentrations. The results also showed a relationship between unconfined compressive strength and calcium carbonate content and pH value.

This paper describes the effect of binder and fibre quantity on the mechanical behaviour of a soft soil stabilised with binders and reinforced with steel fibres. Four types of tests were carried out – unconfined compressive strength (UCS), direct tensile strength (DTS), split tensile strength (STS) and flexural strength (FS) tests. The effects of binder quantity (with and without steel fibres) and the effects of fibre quantity were analysed. The results obtained showed that the compressive strength, tensile strength and stiffness increased with binder quantity, but, with the addition of steel fibres, the behaviour changed depending on the strain mechanism of each test. In general, the presence of a low quantity of steel fibres had a detrimental effect in terms of UCS and a negligible impact on the STS, while a beneficial effect was found for DTS and FS. As the fibre quantity was increased, the UCS, STS and FS tests revealed a decrease in brittleness, while the DTS tests showed brittle behaviour with an abrupt and complete loss of tensile strength after failure. The relationships between compressive and tensile strengths are presented in the paper.

This paper provides an overview of the PISA design model recently developed for laterally loaded offshore wind turbine monopiles through a major European joint-industry academic research project, the PISA Project. The focus was on large diameter, relatively rigid piles, with low length to diameter (L/D) ratios, embedded in clay soils of different strength characteristics, sand soils of different densities and in layered soils combining clays and sands. The resulting design model introduces new procedures for site specific calibration of soil reaction curves that can be applied within a one-dimensional (1D), Winkler-type, computational model. This paper summarises the results and key conclusions from PISA, including design methods for (a) stiff glacial clay till (Cowden till), (b) brittle stiff plastic clay (London clay), (c) soft clay (Bothkennar clay), (d) sand of varying densities (Dunkirk), and, (e) layered profiles (combining soils from (a) to (d)). The results indicate that the homogeneous soil reaction curves applied appropriately for layered profiles in the 1D PISA design model provide a very good fit to the three-dimensional finite element (3D FE) calculations, particularly for profiles relevant to current European offshore wind farm sites. Only a small number of cases, involving soft clay, very dense sand and L/D = 2 monopiles, would appear to require more detailed and bespoke analysis.

This work studies the effect of cyclic loading on the behaviour of a soft soil chemically stabilized with Portland cement and blast furnace granulated slag (proportion 75/25) and reinforced with steel fibres. The influence on accumulated permanent axial strain and on the unconfined compressive strength and stiffness, determined by unconfined compression strength tests, is evaluated for different numbers of load cycles applied initially to the samples. For the conditions tested, the results of the cyclic stage indicate there is a number of load cycles below which the accumulated permanent axial strain increases with the number of cycles, whereas above it, it remains almost constant. The results of the UCS tests show an increase in strength with the number of cycles, which is more pronounced in the tests performed with a low number of cycles. It was also observed an increase in stiffness until 2500 cycles were reached, while for higher number of cycles the opposite occurs.

The prediction of induced ground movements and the potential damage to existing structures and services is paramount when building deep excavations in an urban environment. In order to obtain a reasonable prediction advanced constitutive models need to be employed, so that the behaviour of the soil can be adequately reproduced under different stress conditions. The calibration of such models is complex and often requires optimisation, as a large number of parameters need to be determined from the available ground investigation data, while also ensuring their consistency with the initial ground conditions. This paper presents the calibration process of advanced constitutive models employed to simulate the excavation of the Ivens shaft in Lisbon, Portugal. The data from both historic and new laboratory and field testing is employed in the calibration procedure. In order to assess and validate the suitability of the derived model parameters, a back-analysis of the nearby Baixa-Chiado metro station excavation is carried out and its results are presented and discussed.