Abstract: Offshore wind turbines play a key part in the renewable energy strategy in the UK and Europe as well as in other parts of the world (for example, China). The majority of current developments, certainly in UK waters, have taken place in relatively shallow water and close to shore. This limits the scale of the engineering to relatively simple structures, such as those using monopile foundations, and these have been the most common design to date, in UK waters. However, as larger turbines are designed, or they are placed in deeper water, it will be necessary to use multi-footing structures such as tripods or jackets. For these designs, the tension on the upwind footing becomes the critical design condition. Driven pile foundations could be used, as could suction-installed foundations. However, in this paper, we present another concept-the use of helical pile foundations. These foundations are routinely applied onshore where large tension capacities are required. However, for use offshore, a significant upscaling of the technology will be needed, particularly of the equipment required for installation of the piles. A clear understanding of the relevant geotechnical engineering will be needed if this upscaling is to be successful.

Abstract: In this paper, we show some recent experimental applications of Brillouin optical time-domain analysis (BOTDA) based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors.

Abstract: National Science Foundation (U.S.) (Origami Design for Integration of Self-assembling Systems for Engineering Innovation (ODISSEI Grant No. EFRI-1240383))

Abstract: Despite the growth of the offshore wind industry, there are currently doubts relating to the design of wind facilities in the sea. This paper expounds current, already identified structural uncertainties: problems for soil characterization and transition piece (TP) design. This document also introduces new doubts or issues to be researched in the near future in this field (wave theory, scour process, wave load actions, scale difficulty, etc.), not as yet identified due to the scarce experience in the offshore wind industry. With this in mind, technical offshore wind standards related to foundation design have been reviewed.

Abstract: A response spectrum analysis (RSA) procedure, which estimates the peak response directly from the earthquake design spectrum, is available for the preliminary phase of design and safety eva...

Abstract: Jacket structures are still at the early stage of their development for use in the offshore wind industry. The aim of this paper is to investigate the effect of the soil-structure interaction on the response of an offshore wind turbine with a jacket-type foundation. For this purpose, two different models of flexible foundation-the p-y model and the p-y model considering pile groups effect-are employed to compare the dynamic responses with the fixed-base model. The modal analysis and the coupled dynamic analysis are carried out under deterministic and stochastic conditions. The influence of the soil-structure interaction on the response of the jacket foundation predicts that the flexible foundation model is necessary to estimate the loads of the offshore wind turbine structure well. It is suggested that during fatigue analysis the pile group effect should be considered for the jacket foundation.

Abstract: The authors acknowledge funding from the UK EPSRC, the MEXT KAKENHI (Grant No. 21340100), the Royal Society, the Wolfson Foundation, and the Max Planck Society.

Abstract: Reinforcement measures are often used in high-arch dams with complicated geological foundations. The geomechanical model test is an effective method to study the global stability of arch dams and to evaluate the reinforcement effects of foundation treatments. The block masonry technique was developed to simulate the jointed rock mass, tectonic discontinuities, and reinforcement measures. A tailor-made low-strength binder and small blocks were developed to simulate the strength and deformation of the jointed rock mass and discontinuities, respectively. We applied this technique to geomechanical model tests of the Dagangshan arch dam with and without foundation reinforcements. A rupture test was conducted, and the stress and displacement distribution of the dam and abutments were recorded; the failure mechanisms and processes were explored. The reinforcement effects of the foundation treatment were evaluated by comparing the test results of the models with and without foundation reinforcements. Our analysis indicates that foundation reinforcements can improve the stress distribution, decrease deformation, prevent slides, reduce fault movement, and improve the global stability of high-arch dams.

Abstract: Industrial consortium in Reservoir Simulation and Modelling; Foundation CMG; Alberta Innovates.

Abstract: The nonlinear response of shallow foundations when subjected to combined loading has attracted the attention of the research engineering community over the last few decades, providing promising evidence for incorporation of such response in design provisions. Failure in the form of soil yielding or foundation uplifting may accommodate high ductility demand and increase the safety margins of the whole structure. However, increased permanent displacement and rotation may occur. This paper explores the concept of shallow soil improvement as a means to locally increase soil strength and thus limit rocking-induced settlement. Bearing in mind that the rocking mechanism is relatively shallow, failure may be contained in a soil layer of known properties that extends to a shallow depth beneath the foundation. The performance of a system in poor soil conditions, on an ideal soil profile, and on improved soil profiles was explored through a series of centrifuge tests at the Center for Earthquake Engineering ...

Abstract: Effects of the embedded monopile foundation on the local distributions of pore water pressure, soil stresses, and liquefaction are investigated in this study using a three-dimensional integrated numerical model. The model is based on a Reynolds-Averaged Navier-Stokes wave module and a fully dynamic poroelastic seabed module and has been validated with the analytical solution and experimental data. Results show that, compared to the situation without an embedded foundation, the embedded monopile foundation increases and decreases the maximum pore water pressure in the seabed around and below the foundation, respectively. The embedded monopile foundation also significantly modifies the distributions of the maximum effective soil stress around the foundation and causes a local concentration of soil stress below the two lower corners of foundation. A parametric study reveals that the effects of embedded monopile foundation on pore water pressure increase as the degrees of saturation and soil permeability decrease. The embedded monopile foundation tends to decrease the liquefaction depth around the structure, and this effect is relatively more obvious for greater degrees of saturation, greater soil permeabilities, and smaller wave heights.

Abstract: A composite bucket shallow foundation (CBSF) has been proposed by Tianjin University to adapt the offshore soft geological conditions of China for wind turbines. Vertical bearing capacity modelling and observation tests regarding the CBSF are performed. The test results are accompanied by numerical simulations to provide a better understanding of the failure mechanism of the CBSF. The upper limit of the vertical bearing capacity of the bucket foundation is derived through the upper bound theorem of classical plasticity theory according to the failure mechanism. The soil damage rate is specified as a new empirical parameter in the formula and is defined as the rate between the thickness of the soil that is broken inside the foundation and the radius of the foundation, which indicates the range of soil failure. Furthermore, the range of the soil damage rate is obtained through vertical bearing capacity model tests. The relationship of the bearing capacity factor Nq and Nγ with the friction angle is also dis...

Abstract: Recent studies have highlighted the potential benefits of inelastic foundation response during seismic shaking. According to an emerging seismic design scheme, termed rocking isolation, the foundation is intentionally under–designed to promote rocking and limit the inertia transmitted to the structure. Such reversal of capacity design may improve the seismic performance, drastically increasing the safety margins. However, the benefit comes at the expense of permanent settlement and rotation, which may threaten post-earthquake functionality. Such undesired deformation can be maintained within tolerable limits, provided that the safety factor against vertical loading FSV is adequately large. In such a case, the response is uplifting–dominated and the accumulation of settlement can be limited. However, this is not always feasible as the soil properties may not be ideal. Shallow soil improvement may offer a viable solution and is therefore worth investigating. Its efficiency is related to the nature of rocking, which tends to mobilize a shallow stress bulb. To this end, a series of shaking table tests are conducted, using an idealized slender bridge pier as conceptual prototype. Two systems are studied, both lying on a square foundation of width B. The first corresponds to a lightly-loaded and the second to a heavily-loaded structure. The two systems are first tested on poor and ideal soil conditions to demonstrate the necessity for soil improvement. Then, the efficiency of shallow soil improvement is studied by investigating their performance on soil crusts of depth z/B = 0.5 and 1. It is shown that a z/B = 1 dense sand crust is enough to achieve practically the same performance with the ideal case of dense sand. A shallower z/B = 0.5 improvement layer may also be considered, depending on design requirements. The efficiency of the soil improvement is ameliorated with the increase of rotation amplitude, and with the number of the cycles of the seismic motion.

Abstract: Mumbai city is the financial capital of India with the highest population density and formed by reclamation of land over time from original seven different islands. As per Indian seismic design code IS 1893-Part 1, Mumbai city is located in Zone III, hence may experience moderate intensity earthquake which may lead to liquefaction of some typical soil sites of Mumbai city. In this paper, using available recent procedures for liquefaction analysis, seismic liquefaction hazard maps for Mumbai city are prepared. Also the typical coastal soft soil strata of Mumbai may be prone to soil amplification for different bed rock earthquake motions and the present study shows that typical ranges of soil amplification factor for bed rock acceleration are 1.2–3.5. Hence, construction of pile foundation, which is mostly used for the effective use of the most precious land of Mumbai city for construction of high rise buildings, need special attention in design when such possibly liquefied soil strata with soil amplification during moderate earthquake intensity is considered. Present study shows the response of pile foundation in both non-liquefied and liquefied soil by considering both kinematic and inertial responses in terms of displacement and bending moments of piles, which are necessary to consider for seismic design of pile foundation in typical Mumbai soil.

Abstract: As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offshore environments. Particular focus of this paper is on the foundation instability and its failure mechanisms as well as the relevant theory advances for the prevailing foundation types in both shallow and deep water depths. Piles, spudcans, gravity bases, suction caissons, and plate anchors are detailed in this paper. The failure phenomena and mechanisms for each type of foundations are identified and summarized, respectively. The theoretical approaches along with sophisticated empirical solutions for the bearing capacity problems are then presented. The major challenges are from flow-structure-soil coupling processes, rigorous constitutive modeling of cyclic behaviors of marine sediments, and the spatial variability of soil properties for large-spreading structures. Further researches are suggested to reveal the instability mechanisms for underpinning the evolution of offshore foundations.

Abstract: A series of dynamic centrifuge experiments involving a soil-structure model were performed to investigate the influence of ground motion characteristics on site performance and soil-foundation-stru...

Abstract: Tubular steel towers are the most common supporting structure of wind converters. The towers’ foundation covers an important part of the initial cost and its configuration depends heavily on the type of subsoil. Onshore structures are founded on spread footing foundations or pile foundations with the first being the commonest. In these spread footing foundations, the tower is either embedded in the concrete foundation slab or the tower bottom flange is anchored to the concrete by means of pretensioned bolts. This anchoring of the steel tower on the concrete foundation is very rarely analyzed separately and recent failures due to inadequate design have alerted the wind industry towards the solution of the problem. For the purposes of the analytical and numerical approaches, two alternative types of foundation dimensioning are investigated. The tower properties of the two configurations are the same, providing the same loading and material data. The analytical study of the foundation anchoring is performed with the use of the equivalent ring method and the numerical verification of the two foundation solutions is performed with the use of a detailed micro model. The same micro model is used for the calculation of the fatigue life of the tower bottom joint following the damage accumulation method. In both foundation solutions, the total cross sectional area of the anchor bolts is proved to be the decisive factor for the selection of bolt size and number. The size of the tower bottom diameter plays also an important role on the maximum number and size of bolts used. Both analytical and numerical results are in good agreement and valuable outcomes are emerging from the comparative study on the foundation dimensioning of contemporary structures.

Abstract: During large earthquakes, soil liquefaction has repeatedly damaged many buildings with shallow foundations. Many researchers have continuously worked to develop more reliable countermeasure techniques apposite to the foundation soils of existing buildings. However, most countermeasure techniques available in the current practice are either too expensive or applicable only to new construction sites. Lowering the degree of saturation by artificially injecting air is a newly developed, innovative technique that significantly improves the liquefaction strength of soil. This paper describes a series of centrifuge tests for evaluating the effectiveness of this technique by applying it to the foundation soil underlying shallow foundations of relatively light structures, such as residential buildings. Models of saturated medium dense sand beds with shallow foundations were shaken in a centrifuge. Except for benchmark models, air was injected into the soil in-flight before the shaking event, which lowered the degr...

Abstract: In Tanzania, standard penetration test (SPT) is the most commonly used in situ test for foundation design site investigations. In an effort to increase the amount of geotechnical information at low ...