Embankment and dyke stability in the Netherlands has always been evaluated by effective stress analysis. The subsoil of most of these structures is organic, weak and soft, but the internal friction angle of these soils is surprisingly high. Empirical methods are used to obtain acceptable, reduced values of friction angle from triaxial tests for use in stability analyses. It appears possible, however, to do full justice to the peculiar combination of low strength and stiffness and high friction angle by means of the finite-element method using a viscous version of the Cam-clay model. All parameters of the model are found from a single test in a constant-rate-of-strain K ₀ oedometer. The approach is illustrated by two case histories, after first providing insight into the peculiar properties of the Dutch soils, and the manner in which they are dealt with.

Precast high-strength prestressed concrete pipe piles installed by the jacking method have received wide use as deep foundations in China. Adoption of appropriate termination criteria during installation is the key issue to ensure design capacity or avoid conservative design for jacked piles. A database including 1228 field load tests on jacked concrete pipe piles is collected in this study to establish empirical correlations between the final jacking force and the ultimate capacity. Using the pile slenderness ratio as the fundamental parameter, a total of 14 correlations are derived to apply for various categories of soil conditions. Among them, the ratio of pile capacity to jacking force for piles in stiff clay and firm clay exhibits the greatest magnitude and trend of increase with increasing pile slenderness ratio. Moreover, two jacked concrete pipe piles in silty clay are instrumented and load-tested as an independent case to examine the consistency of the proposed correlations. The two test piles are installed in accordance with a double-control termination criterion that involves the requirements of both final penetration and final jacking force. The load transfer behaviour of the piles has revealed that their performances satisfy all the design requirements.

Vertical vibration tests were conducted using model footings of different size and mass, resting on the surface of a finite sand layer with different height-to-width ratios, which was underlain either by a rigid concrete base or a natural red-earth base. Using the results of resonant frequency, the equivalent stiffness was obtained using the empirical equations available in the literature. The results of the experimental study showed that the rigidity of the finite base has significant influence on the equivalent stiffness of the soil–foundation system. The equivalent stiffness obtained for model footings resting on a finite sand stratum underlain by a rigid concrete base is higher than those obtained under the influence of the natural red-earth base. The increase in dynamic force rating decreases the stiffness of the soil. At a constant height to width (H/B) ratio, for a footing with higher mass ratio when compared with a footing with lower mass ratio, the equivalent stiffness does not decrease significantly with increase in the mass ratio of the model footing, indicating the significant influence of the contact area of the footing. When a layer having significantly larger value of stiffness compared to the upper layer is present at shallow depth, it can be treated to act as a finite sand stratum.

In this paper a new mathematical function is proposed for describing the S-shape relationship in both normal x and y scale and the semi-logarithmic x and y scale. Basic features of the proposed function have been demonstrated. The proposed function has then been used to simulate the S-shape relationship for seven categories of engineering phenomena. It is seen that the proposed mathematical function has a great potential for representing various S-shape relationships and provides a powerful tool for characterising properties of materials or response of systems; it is thus useful for further numerical analysis.

Renewable offshore energy structures experience unusually high levels of cyclic loading under storm and operating conditions. Laboratory and full-scale tests provide one route to develop rational foundation design approaches for such structures. Analytical approaches may also be developed from soil element testing and modelling. This paper outlines preliminary results from such a study. Computer-controlled stress path triaxial equipment, employing high-resolution local strain instrumentation, is adopted for experiments on Dunkerque and Fontainebleau sands designed to support parallel full-scale field and laboratory-model testing programmes involving axial pile loading. The triaxial experiments comprise suites of constant-volume uniform cyclic tests on K ₀ over-consolidated specimens employing different amplitudes, performed in conjunction with static and multi-stage experiments that examine the effects of non-uniform cyclic loading. Preliminary results reveal the relationships between cyclic deviator stress, mean effective stress changes and number of cycles, as well as patterns of permanent and cyclic strain development.

A review of the load applied to multi-pile offshore wind turbine foundations is presented, from which the need to consider the response to axial cyclic loading is emphasised. The paucity of available data on field tests on driven piles in sand is noted. A comprehensive data set of multiple axial cyclic and static tests conducted on seven industrial-scale steel pipe-piles at a marine sand site in Dunkerque, France, is re-examined in this paper. The effects of cycling on axial capacity are interpreted by reference to stable, metastable or unstable zones defined in a normalised cyclic stability interaction diagram. A detailed analysis is made of the load–displacement and stiffness response associated with each mode of cycling. It is shown that in all cases the piles' cyclic stiffnesses show only minor changes until cyclic failure is approached. The patterns of permanent cyclic strain accumulation are sensitive to the applied mean and cyclic loading levels. Whereas displacements accumulate rapidly over just a few cycles in the unstable zone, extended cycling in the stable zone leads to minimal accumulated displacements and constant transient cyclic displacements.

Offshore wind turbines are currently considered as a reliable source of renewable energy in the UK. These structures, owing to their slender nature, are dynamically sensitive at low frequencies, the first modal frequency of the system (less than 1 Hz) being very close to that of the excitation frequencies. The majority of operational offshore wind turbines situated in UK waters are founded on monopiles in water depths up to 30 m. For future development rounds where water depths are up to 70 m, alternative foundation arrangements are needed. To date there have been no long-term observations of the performance of these relatively novel structures. Monitoring of a limited number of offshore wind turbines has indicated a departure of the system dynamics from the design requirements. This paper summarises the results from a series of 1:100 scale tests of a V120 Vestas turbine supported on two types of foundation: monopiles and tetrapod suction caissons. The test bed used consisted of kaolin clay and sand. Up to 1·25 million loading cycles were applied to the scaled model, and the dynamic properties of the system were monitored. The results provide an insight into the long-term performance. Some interesting dynamic soil–structure interaction issues are identified and discussed.