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A new geotechno-stratigraphic model for Quaternary deposits in the Western Irish Sea Mud Belt area is presented. This area, located in the North Irish Sea, has been heavily influenced by the advance and retreat of the British and Irish Ice Sheet during the last glaciation and subsequent Holocene marine transgression. This study uses a synthesis of lithostratigraphy, geotechnical data (from in situ cone penetration testing) and seismic profiles to generate a stratigraphic framework describing the geometry, distribution and characteristics of Quaternary deposits in an area of the Western Irish Sea Mud Belt at increased resolution. Within a regional context, this stratigraphy is compared with other established offshore stratigraphies in the Irish Sea and terrestrial successions. Four stratigraphic units are identified consisting of a basal subglacial (lodgement) till (Unit 4) emplaced by the Irish Sea Ice Stream. Unit 4 overlies irregular bedrock and is overlain in turn by glaciomarine to glaciolacustrine, ice-proximal outwash and glaciomarine ice-proximal sand and sandy muds (Units 3 and 2 respectively; previously undifferentiated). A thick succession (up to 27 m) of Holocene marine muds (Unit 1) caps the sequence up to the contemporary seabed. Results show that these deposits, and their geotechnical properties, have significant implications for the anthropogenic use of the area, such as the development of offshore renewable energy infrastructure. Revealed are relatively thick (up to 30 m) weak, under-consolidated sediments at the surface and highly heterogeneous, often over-consolidated, sediments that have limited groundtruthing at depth. Furthermore, localised shallow gas is imaged on seismic profiles. The influence on the geotechnical properties of the sediments by this gas revealed no significant effect on shear strength values from cone penetration testing data, although it may have implications for the long-term behaviour of the sediments.

For the majority of offshore jackets, driven piles are the preferred foundation solution; however difficult soil conditions may preclude conventional pile driving. In such circumstances, methods of grouting a pile into an oversized hole or drilling and underreaming for a cast-in-place pile have received considerable attention. Drilled-and-grouted (D&G) piles are normally used in challenging geologies, such as very dense sands, very stiff clays and in calcareous deposits. However, D&G piles are normally time-consuming to construct. To address this challenge, the MIDOS pile system, which minimizes the number of offshore operations, was created and subjected to a suite of field tests. Cyclic tests were conducted on a pile installed in a silica sand deposit, where over 1000 loading cycles in between 1000 kN and 5000 kN (in tension) were applied. The evaluation of the cyclic test data clearly shows that the serviceability of the pile is unaffected by the cyclic loads. A feasibility study of the MIDOS pile in carbonate sands (Dog's Bay sand) was also explored in a laboratory test program. Carbonate sands are particularly relevant for drilled foundation solutions as the shaft friction of driven piles is typically very low due to the high radial contraction of such material adjacent to the pile shaft during impact driving. A finite element model (FEM) developed for this calcareous sand was used to compare the lab test results. The outcome of the laboratory testing program demonstrated that the MIDOS pile would have similar geotechnical and structural properties in both calcareous and siliceous deposits, suggesting that this novel offshore foundation type is suitable for a range of sand conditions.

This paper presents the results of field tests performed to investigate the field behaviour of winged-monopile foundations. The principle of the winged monopile is that steel plates are attached to a standard monopile (in the area near the ground or seabed surface) to increase the foundation stiffness and lateral resistance. The experimental tests described in this paper consisted of load tested driven instrumented prototype scale standard (reference) monopiles and piles with varying wing geometries at two sand sites. The overall load–displacement performance and mobilised bending moment profiles were examined to assess the potential benefits of adding wings to monopiles. Experimental p–y curves were developed for the piles to analyse how the presence of wings influenced the soil–structure interaction of the foundation system. The use of simplified p–y methods for predicting the winged-pile response was assessed. The experiments proved that the addition of wings greatly improved the lateral resistance and stiffness of the piles; however, the results suggest that conventional p–y curve methods are limited as they cannot account for the effect that the enhanced stresses mobilised by the wings have on the strength and stiffness response of the pile below the wing location.

At low confining stresses, calcareous sands exhibit many similar characteristics to silica sand deposits; however, at high stresses their shearing behaviour is quite different, exhibiting strong contraction due to grain crushing. Therefore, calcareous deposits can create significant challenges for driven pile foundations where the high installation energy causes particle damage, radial contraction and very low pile shaft friction. Drilled-and-grouted piles are often preferred in calcareous conditions. As an alternative to conventional foundation solutions, a novel pile has been developed based on the mixed-in-place technology. Two carbonate sands, the Dog's Bay foramol carbonate sand and the Ballyconneely sand, which is a calcitic carbonate algal sand, have been tested in the laboratory to investigate the geotechnical behaviour of these two sediments, which have different genesis and mechanical characteristics. The sands were mixed with concrete grout at cement-to-sand ratios of 15, 25 and 35%, and at a water-to-cement ratio of 0·4 to simulate the mixed-in-place pile installation technique. The results show similar geotechnical and structural performance for both sands.

The behaviour of calcareous (or carbonate) soils often presents significant foundation challenges regarding the construction of offshore hydrocarbon facilities. The presence of carbonate deposits at many strategic petrochemical reserves implies the necessity to study the behaviour of these soils. Driven piles, normally used as deep foundation elements for oil and gas platforms are normally avoided in these geological conditions as the impact operations lead to a degradation of the sand properties decreasing the shaft capacities. Drilled-and-grouted (D&G) piles overcome many of the technical limitations associated with impact piling in carbonate deposits, however D&G piles are both expensive and time consuming to construct. A novel mixed-in-place pile has been developed that provides a technically and economically efficient solution for carbonate soils. This technology minimizes the number of offshore operations and is therefore significantly quicker than D&G piles and therefore more cost effective. Several laboratory tests and in situ tests have been performed to assess its behaviour in both silica and carbonate sands. This research uses the results of recent laboratory experiments on the mixed-in-place pile on both silica and calcareous sands to develop a Finite Element Model (FEM) of full scale piles to test their potential bearing capacities for oil and gas platforms.

Over the past 5 years, a substantial research effort aimed at optimising the design of offshore wind turbines has led to significant reductions in the projected cost of developing offshore wind. Optimising the geotechnical design of these structures, through modern analysis techniques such as 3D Finite Element Modelling (FEM), has played a key role in helping to reduce costs. This paper presents a methodology for accurately modelling monopile behaviour using Cone Penetration Test (CPT) data to calibrate the non-linear stress dependent Hardening Soil (HS) model. The methodology is validated by comparing the modelled behaviour to field tests on a range of pile geometries. The paper also demonstrates how the soil-pile reaction response curves can be extracted from the FE model by isolating the stresses on each element of the pile. The contribution of each component to the overall lateral resistance is shown to vary with the pile geometry and is examined using the extracted soil reaction curves.

In recent times, interest in dynamically installed foundation systems for deep-sea construction has increased; however, these foundation systems are still under development and need quantification of various soil parameters with different perspectives. For the design of dynamically installed foundations, it is essential to assess the strain-rate effect on very soft soils. The T-bar has been widely used to characterize soft offshore sediments, such as silt and clay, and there is extensive existing literature on the interpretation of test results. Strain-rate dependence has not previously been fully examined for T-bar tests in very soft clay at very high rates of penetration. This paper examines this aspect using a physical model test. A 65-cm-thick kaolin clay bed was formed using vacuum consolidation. A T-bar was driven into the clay bed at rates that varied from 0.1 cm/s to 60 cm/s. The tests revealed that the resistance factor increased by 9 % for every 10-fold increase in the penetration rate for the material tested in this research.

A research study was recently completed by University College Dublin to examine the performance of various pile types including open steel tubular piles, concrete precast piles, and helical piers. At the outset of this project, one of the key risks identified was that the concrete piles could not be installed to the target depth due to (i) insufficient energy from the available hammer and (ii) the onset of pile material damage. In order to mitigate this risk a detailed pile driveability analysis was completed to predict the installation performance during driving. Selecting an appropriate model for predicting the Static Resistance to Driving (SRD) was seen as a critical component of the driveability process in order to predict reasonable stresses and blow counts. This paper describes the procedures adopted for a base case driveability analysis and the outcome of the pile installations. A comparison of the SRD using other models (including the API and IC-05 methods) was conducted and the results we...

This technical note presents the results of a field investigation into pile aging in soft clay which was conducted over a period of ten years. Static load tests were conducted after the excess pore pressure generated by the installation of 6 m long driven concrete piles were fully equalised. These tests allowed the time-capacity aging profile to be established. A normalised capacity-time trend established for the case history is seen to be consistent with the response observed from a wider database of pile tests in clay compiled from the literature. A simple reliability based design example is provided to highlight the positive impact that pile aging could have for industrial practice. Author has checked copyright 19/8/2013. SB.

This paper describes an experimental investigation designed to assess the impact of pile end condition on the capacity of piles installed in soft clay. A series of field tests are described in which instrumented open-ended and closed-ended model piles were jacked into soft clay. The radial stresses, pore pressures, and load distribution were recorded throughout installation, equalization, and load-testing. Although the total stress and pore pressure developed during installation were related to the degree of soil plugging, the radial effective stress that controls the shaft resistance was shown to be independent of the mode of penetration. The long-term shaft capacity of the open-ended pile was closely comparable to that developed by closed-ended piles, suggesting a limited influence of end condition on the fully equalized shaft resistance. In contrast to the shaft resistance, the base capacity was highly dependent on the degree of plugging. Deposited by bulk import RB 19/02/13

The rapid expansion of the offshore wind sector, coupled with increasing demand for high rise structures, has placed renewed demand on the driven piling market. In light of this industry growth, this paper reviews the evolution of design approaches for calculating the shaft capacity of displacement piles installed in cohesive soils. The transition from traditional total stress design towards effective stress methods is described. Complex stress–strain changes occur during pile installation, equalisation and load testing and as a consequence, the selection of parameters for use in conventional earth-pressure type effective stress approaches is not straight-forward. These problems have led to the development of empirical correlations between shaft resistance and in situ tests, such as the cone penetration tests. However, many of these approaches are limited because they were developed for specific geological conditions. Significant insight into pile behaviour has been obtained from recent model pile tests, which included reliable measurements of radial effective stresses. These tests have allowed factors such as friction fatigue and interface friction to be included explicitly in design methods. Whilst analytical methods have been developed to investigate pile response, these techniques cannot yet fully describe the complete stress–strain history experienced by driven piles. The use of analytical methods in examining features of pile behaviour, such as the development of pore pressure during installation and the effects of pile end geometry on pile capacity, is discussed. Deposited by bulk import TS 01.03.13

In recent years, fibre Bragg grating (FBG) sensors have emerged as a relatively new strain sensing technology for civil engineering applications. This paper presents a field trial to assess the feasibility of using FBG sensor arrays to measure strain in driven steel piles. Two FBG arrays were installed in grooves within the wall of an open-ended steel pile such that the finished profile was completely flush with the pile shaft. The pile was then driven into a dense sand deposit using an impact hammer to provide the required installation energy. The FBG gauges were monitored throughout driving in conjunction with accelerometers to quantify the scale of the hammer impacts. The FBG sensors were subjected to hammer blows that yielded pile accelerations between 500 g and 1400 g during installation. The fibre optic sensors were measured throughout driving, where they were observed to respond to the hammer impacts, showing a rapid increase in strain and a return to their initial values between hammer strikes. After installation, a lateral load test was performed with independent load measuring devices. Excellent agreement was observed between the measured moments and those inferred from the FBG strain output. The output of this trial demonstrates that FBG strain sensors are a viable means of measuring load transfer in foundation systems and are suitably robust to withstand high pile driving accelerations.

Lateral loading is often the governing design criteria for piles supporting offshore wind turbines and with the recent growth of this sector, the reliability of traditional design approaches is receiving renewed interest. To accurately assess the behavior of a laterally loaded pile requires a detailed understanding of the soil reaction that is mobilized as the lateral deflection of the pile occurs. Currently, the p-y curve method is widely adopted to model the response of laterally loaded piles. The limitations of existing p-y formulations are widely known, and there is acceptance that load tests on large-diameter stiff monopiles are urgently required to formulate appropriate design methods. However, interpretation of the data from instrumentation placed on stiff monopiles is not straightforward. This paper proposes an optimization technique to derive the soil reaction profile along the shaft of instrumented piles, from which the correlated p-y curves can then be obtained. The method considers force equilibrium, pile deflection, and additional boundary conditions. A set of fourth-order polynomial equations are assumed to model the soil reaction profile under each load step during a monotonic load test. By minimizing the difference between the measured and calculated bending moment and considering equilibrium of the shear forces acting on the pile, the soil reaction profile and the concentrated tip resistance can be obtained simultaneously. A stiff instrumented test pile installed in over-consolidated sand was load tested and the results were used to test the performance of the proposed method. The results are compared with other methods used in literature and practice. The method provides a consistent framework to derive p-y curves from measured strain data. The results of the field test and derived p-y curves confirmed that existing design methods do not accurately capture the lateral loading response of piles in dense sand.

Offshore piles are subjected to complex loading regimes, which include both rapidly applied static and cyclic loads. This note describes an experimental investigation conducted in order to assess the factors influencing the response of offshore piles to these loading conditions. The tests were performed using instrumented model piles installed in soft clay. During cyclic loading, the piles demonstrated a transition from stable to unstable behaviour when the applied loads reached a specific load threshold. Stable behaviour was defined when increments of plastic displacement decreased as the number of load cycles increased. During stable behaviour, radial effective stresses at the pile-soil interface remained constant. During unstable behaviour, pore pressures at the pile-soil interface rose as the number of cycles increased. This resulted in reduced radial effective stresses and progressively increasing displacement rates. Due to the presence of these excess pore pressures, the shaft resistance recorded during static load tests, performed after a period of unstable cyclic loading, were lower than those measured on piles where the pore pressure was fully equalised. However, the axial resistance was seen to be rate dependent. Fast loading of the pile resulted in reductions of pore water pressure at the soil-pile interface and enhanced shaft resistance which could overcome the negative effect caused by cyclic loading. Deposited by bulk import SB. 19/02/2013

The paper considers the current state of the art for estimating the pull-out capacity of driven open-ended piles used to support wind turbine foundations founded on sand. The latest edition of the American Petroleum Institute guidelines for pile design includes a conventional earth pressure approach and four alternative cone penetration test (CPT) methods for estimating pile shaft resistance in sand. A database of open-ended pile tests was used to assess the predictive reliability of the design approaches. While the earth pressure approach was unreliable, exhibiting bias with pile slenderness and sand relative density, the CPT methods were shown to provide improved and relatively consistent estimates of pile capacity. However, the tension loads experienced by wind turbine foundations are significantly higher than those applied to piles in the database. When the CPT methods were used to estimate the pile length required to support a 5 MW turbine installed in typical offshore soil conditions, the CPT methods provided a wide range of predicted pile lengths. The reasons for this divergence are discussed and an alternative framework for considering driven pile shaft resistance is put forward. Deposited by bulk import TS 01.03.13

Cet article presente les resultats d'une serie d'essais sur le terrain effectues dans le but d'etudier les effets de la methode d'installation sur la resistance de l'arbre d'un pieu developpee lors de l'installation d'un pieu dans un silt argileux mou. Les essais ont ete effectues sur des pieux ayant subit differents niveaux de chargement cyclique durant l'installation. Les resultats des essais indiquent que la contrainte totale radiale, la pression interstitielle, et la contrainte de cisaillement sur l'arbre du pieu lors de l'installation, sont fortement affectes par la procedure d'installation. Ces trois parametres augmentent lorsque la longueur du levier utilise pour l'installation augmente (ou lorsque le nombre d'application cyclique de la charge diminue). Cependant, les contraintes effectives radiales egalisees, qui controlent la capacite de l'arbre du pieu a long terme, sont demeurees inaffectees par la methode d'installation. Une expression simple, qui necessite des resultats d'essais de penetration au cone, de mesures de laboratoire de l'angle de friction a l'interface et de donnees sur la geometrie du pieu, est proposee afin de calculer la resistance de l'arbre.

This paper describes the development of a model instrumented open-ended (pipe) pile. The importance of model geometry and separating the shaft, annular and plug load, and horizontal effective stresses is discussed. A detailed description of the construction of the twin-walled open-ended pile is presented. Particular attention was given to protecting the fragile instrumentation from the rigours of installation and the effects of water ingress. Calibration procedures, which were used to verify the instrument reliability, are also discussed. The final section describes field tests conducted in both loose sand and medium-dense sand deposits, which are used to validate the instrument performance. Deposited by bulk import TS 22.02.13