Ross McAdam | University of Oxford (original) (raw)
Papers by Ross McAdam
Géotechnique, 2022
This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Mu... more This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Multiple undrained high-resolution cyclic triaxial experiments on low-to-medium density intact chalk, along with index and monotonic reference tests, define the conditions under which either thousands of cycles could be applied without any deleterious effect, or failure can be provoked under specified numbers of cycles. Intact chalk's response is shown to differ from that of most saturated soils tested under comparable conditions. While chalk can be reduced to putty by severe two-way displacement-controlled cycling, its behaviour proved stable and nearly linear visco-elastic over much of the one-way, stress controlled, loading space examined, with stiffness improving over thousands of cycles, without loss of undrained shear strength. However, in cases where cyclic failure occurred, the specimens showed little sign of cyclic damage before cracking and movements on discontinuities lead t...
Géotechnique, 2022
Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to ... more Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to inform the interpretation of axial and lateral tests on driven piles. The chalk de-structures when taken to large strains, especially under dynamic loading, leading to remarkably high pore pressures beneath penetrating CPT and driven pile tips, weak putty annuli around their shafts and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explore the chalk's unstable structure and markedly time and rate-dependent mechanical behaviour. A clear hierarchy is found between profiles of peak strength with depth of Brazilian tension (BT), drained and undrained triaxial and direct simple shear (DSS) tests conducted from in-situ stress conditions. Highly instrumented triaxial tests reveal the chalk's unusual effective stress paths, markedly brittle failure behaviour from small strains and the effects of consolidating to higher than in-...
Model tests on two designs of 0.5m diameter transverse flow turbine are described. Measurements w... more Model tests on two designs of 0.5m diameter transverse flow turbine are described. Measurements were made relevant to both the hydrodynamic and structural performance of the turbines, and a variety of conditions were explored (including flow depth, upstream velocity, flow direction, blade pitch, turbine solidity). This paper concentrates particularly on the measurements of loads on the turbine blades.
The Transverse Horizontal Axis Water Turbine (THAWT) has been proposed as a tidal device which ca... more The Transverse Horizontal Axis Water Turbine (THAWT) has been proposed as a tidal device which can be easily scaled and requires fewer foundations, bearings seals and generators than a more conventional axial-flow device. The THAWT device is a horizontally deployed variant of the Darrieus cross-flow turbine, in which the blades can be oriented into a truss configuration to produce long, stiff multi-bay rotors. This thesis establishes and combines a set of numerical models, which predict the hydrodynamic and structural performance of the THAWT device, with sufficient confidence to assess the feasibility of such a device at a full scale installation and to optimise its performance. Tests of 1/20th scale experimental models of the THAWT device have demonstrated that the truss configured device is capable of producing power with an efficiency close to that of the parallel configured turbine. In addition, variations in the configuration of the scale models have indicated how several desi...
This paper describes the outcome of a recently completed research project – known as PISA – on th... more This paper describes the outcome of a recently completed research project – known as PISA – on the development of a new process for the design of monopile foundations for offshore wind turbine support structures. The PISA research was concerned with the use of field testing and three-dimensional (3D) finite element analysis to develop and calibrate a new one-dimensional (1D) design model. The resulting 1D design model is based on the same basic assumptions and principles that underlie the current p-y method, but the method is extended to include additional components of soil reaction acting on the pile, and enhanced to provide an improved representation of the soil-pile interaction behaviour. Mathematical functions – termed ‘soil reaction curves’ – are employed to represent the individual soil reaction components in the 1D design model. Values of the parameters needed to specify the soil reaction curves for a particular design scenario are determined using a set of 3D finite element...
This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed... more This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed in the UK. The research was aimed at developing new design methods for laterally loaded monopile foundations, such as those supporting offshore wind turbine structures. The paper first describes the background to the project and briefly outlines the key research elements completed. The paper concludes with a brief description of the anticipated impact of the work and describes initiatives that have followed since.
Coastal structures, 2019
Large numbers of offshore wind turbines, near-shore bridges and port facilities are supported by ... more Large numbers of offshore wind turbines, near-shore bridges and port facilities are supported by driven piles. The design and installation of such piles is often problematic in Chalk, a low-density, porous, weak carbonate rock, which is present under large areas of NW Europe. There is little guidance available to designers on driveability, axial capacity, the lateral pile resistance which dominates offshore wind turbine monopile behaviour, or on how piles can sustain axial or lateral cyclic loading. This paper describes the ALPACA project which involves comprehensive field testing at a low-to-medium density chalk research test site. The project is developing new design guidance through comprehensive field testing and analysis combined with in-situ testing campaigns and advanced static-and-cyclic laboratory testing on high quality block and rotary core samples.
The recently-completed PISA (PIle Soil Analysis) research project aimed to improve the design of ... more The recently-completed PISA (PIle Soil Analysis) research project aimed to improve the design of monopile foundations for offshore wind turbines (OWT), focusing on laterally-loaded monopiles with length-to-diameter (L/D) ratios between 2 and 6. The project resulted in a novel one-dimensional (1D) design model which overcomes certain limitations in current practice. The PISA 1D design model facilitates rapid design calculations, based on the use of Timoshenko beam theory to represent the monopile. The soil response is modelled via soil reactions, applied along the shaft and at the base of the monopile. The soil reaction curves are determined using a series of three-dimensional (3D) finite element (FE) calibration calculations, performed prior to the design process, spanning a representative design space. A new software tool called PLAXIS MoDeTo (Monopile Design Tool) has been developed based on this design procedure. This design tool facilitates the automatic generation and calculati...
The PISA design model is a procedure for the analysis of monopile foundations for offshore wind t... more The PISA design model is a procedure for the analysis of monopile foundations for offshore wind turbine applications. This design model has been previously calibrated for homogeneous soils; this pa...
Tidal turbine blades are smaller than wind turbine blades yet carry similar bending moments. This... more Tidal turbine blades are smaller than wind turbine blades yet carry similar bending moments. This pro vides a structural challenge and limits how thin the blades can be made, which subsequently affects the hydrodynamic performance of the rotor. Thinner blades generally offer higher performance but require thicker laminates hence are more expensive to build. Opinions vary amongst tidal turbine developers as t o the best compromise for overall cost of energy. The parametric study presented in this paper includes a full structural and hydrodynamic design of a megawatt-sc ale axial flow tidal turbine rotor. Typical tidal turbine si te parameters are assumed in terms of flow speed, turbulence and wave loading based on Gurit's experience of several rotors of th is size. The blades are designed using epoxy composites in accor dance with industry best practice. The blade thickness, chord and twist distribution are varied to find the effect on annual energy production and blade manufactu...
Frontiers in Offshore Geotechnics III, 2015
ABSTRACT There is currently a significant focus on developing offshore wind power in the UK and E... more ABSTRACT There is currently a significant focus on developing offshore wind power in the UK and Europe. The most common foundation type for wind turbines is a single large diameter pile, termed a monopile, on which the turbine is located. As the diameter of such piles is envisaged to increase in future installations, there are concerns that current design methods are not applicable. To explore this problem, the joint industry project PISA has been established, with the aim to develop a new design framework for laterally loaded piles utilised in the offshore wind industry, based on new theoretical developments, numerical modelling and large scale field pile testing. This paper presents an overview of numerical modelling undertaken as part of the project.
Géotechnique Letters, 2015
In recent years, fibre Bragg grating (FBG) sensors have emerged as a relatively new strain sensin... more 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 bet...
Frontiers in Offshore Geotechnics III, 2015
Journal of Geotechnical and Geoenvironmental Engineering
This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress wav... more This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length-to-diameter ratios of 6∶20 were impact driven at an established chalk test site in Kent, United Kingdom. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles' responses under each hammer blow. A high-frequency (5 kHz) fiber optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared the time series of pile head PDA measurements and FBG strains measured below the ground surface. Numerical solutions of the one-dimensional wave equation were optimized by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high-resolution strain measurements are made.
Journal of Waterway, Port, Coastal, and Ocean Engineering
Géotechnique
Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations.... more Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations. Although three-dimensional (3D) finite-element methods are available for the design of monopiles in this context, much of the routine design work is currently conducted using simplified one-dimensional (1D) models based on the p-y method. The p-y method was originally developed for the relatively large embedded length-to-diameter ratio (L/D) piles that are typically employed in offshore oil and gas structures. Concerns exist, however, that this analysis approach may not be appropriate for monopiles with the relatively low values of L/D that are typically adopted for offshore wind turbine structures. This paper describes a new 1D design model for monopile foundations; the model is specifically formulated for offshore wind turbine applications, although the general approach could be adopted for other applications. The model draws on the conventional p-y approach, but extends it to include additional components of soil reaction that act on the pile. The 1D model is calibrated using a set of bespoke 3D finite-element analyses of monopile performance, for pile characteristics and loading conditions that span a predefined design space. The calibrated 1D model provides results that match those obtained from the 3D finite-element calibration analysis, but at a fraction of the computational cost. Moreover, within the calibration space, the 1D model is capable of delivering high-fidelity computations of monopile performance that can be used directly for design purposes. This 1D modelling approach is demonstrated for monopiles installed in a stiff, overconsolidated glacial clay till with a typical North Sea strength and stiffness profile. Although the current form of the model has been developed for homogeneous soil and monotonic loading, it forms a basis from which extensions for soil layering and cyclic loading can be developed. The general approach can be applied to other foundation and soil-structure interaction problems, in which bespoke calibration of a simplified model can lead to more efficient design.
Volume 10: Ocean Renewable Energy
There are two approaches to extracting power from tides — either turbines are placed in areas of ... more There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as ex...
Revue Française de Géotechnique
Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. La... more Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. Large numbers of offshore wind turbines, bridges and port facilities rely on piles driven in chalk. Current European practice assumes ultimate shaft resistances that appear low in comparison with the Chalk’s unconfined compression strength and CPT cone resistance ranges and can impact very significantly on project economics. Little guidance is available on pile driveability, set-up or lateral resistance in chalk, or on how piles driven in chalk can sustain axial or lateral cyclic loading. This paper describes the ALPACA (Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing) project funded by EPSRC and Industry that is developing new design guidance through comprehensive field testing at a well-characterised low-to-medium density test site, supported by analysis of other tests. Field experiments on 36 driven piles, sixteen of which employ high resolution f...
Géotechnique, 2022
This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Mu... more This paper reports the cyclic behaviour of chalk, which has yet to be studied comprehensively. Multiple undrained high-resolution cyclic triaxial experiments on low-to-medium density intact chalk, along with index and monotonic reference tests, define the conditions under which either thousands of cycles could be applied without any deleterious effect, or failure can be provoked under specified numbers of cycles. Intact chalk's response is shown to differ from that of most saturated soils tested under comparable conditions. While chalk can be reduced to putty by severe two-way displacement-controlled cycling, its behaviour proved stable and nearly linear visco-elastic over much of the one-way, stress controlled, loading space examined, with stiffness improving over thousands of cycles, without loss of undrained shear strength. However, in cases where cyclic failure occurred, the specimens showed little sign of cyclic damage before cracking and movements on discontinuities lead t...
Géotechnique, 2022
Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to ... more Low-to-medium density chalk at St Nicholas at Wade, UK, is characterised by intensive testing to inform the interpretation of axial and lateral tests on driven piles. The chalk de-structures when taken to large strains, especially under dynamic loading, leading to remarkably high pore pressures beneath penetrating CPT and driven pile tips, weak putty annuli around their shafts and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explore the chalk's unstable structure and markedly time and rate-dependent mechanical behaviour. A clear hierarchy is found between profiles of peak strength with depth of Brazilian tension (BT), drained and undrained triaxial and direct simple shear (DSS) tests conducted from in-situ stress conditions. Highly instrumented triaxial tests reveal the chalk's unusual effective stress paths, markedly brittle failure behaviour from small strains and the effects of consolidating to higher than in-...
Model tests on two designs of 0.5m diameter transverse flow turbine are described. Measurements w... more Model tests on two designs of 0.5m diameter transverse flow turbine are described. Measurements were made relevant to both the hydrodynamic and structural performance of the turbines, and a variety of conditions were explored (including flow depth, upstream velocity, flow direction, blade pitch, turbine solidity). This paper concentrates particularly on the measurements of loads on the turbine blades.
The Transverse Horizontal Axis Water Turbine (THAWT) has been proposed as a tidal device which ca... more The Transverse Horizontal Axis Water Turbine (THAWT) has been proposed as a tidal device which can be easily scaled and requires fewer foundations, bearings seals and generators than a more conventional axial-flow device. The THAWT device is a horizontally deployed variant of the Darrieus cross-flow turbine, in which the blades can be oriented into a truss configuration to produce long, stiff multi-bay rotors. This thesis establishes and combines a set of numerical models, which predict the hydrodynamic and structural performance of the THAWT device, with sufficient confidence to assess the feasibility of such a device at a full scale installation and to optimise its performance. Tests of 1/20th scale experimental models of the THAWT device have demonstrated that the truss configured device is capable of producing power with an efficiency close to that of the parallel configured turbine. In addition, variations in the configuration of the scale models have indicated how several desi...
This paper describes the outcome of a recently completed research project – known as PISA – on th... more This paper describes the outcome of a recently completed research project – known as PISA – on the development of a new process for the design of monopile foundations for offshore wind turbine support structures. The PISA research was concerned with the use of field testing and three-dimensional (3D) finite element analysis to develop and calibrate a new one-dimensional (1D) design model. The resulting 1D design model is based on the same basic assumptions and principles that underlie the current p-y method, but the method is extended to include additional components of soil reaction acting on the pile, and enhanced to provide an improved representation of the soil-pile interaction behaviour. Mathematical functions – termed ‘soil reaction curves’ – are employed to represent the individual soil reaction components in the 1D design model. Values of the parameters needed to specify the soil reaction curves for a particular design scenario are determined using a set of 3D finite element...
This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed... more This paper provides a brief overview of the Pile Soil Analysis (PISA) project, recently completed in the UK. The research was aimed at developing new design methods for laterally loaded monopile foundations, such as those supporting offshore wind turbine structures. The paper first describes the background to the project and briefly outlines the key research elements completed. The paper concludes with a brief description of the anticipated impact of the work and describes initiatives that have followed since.
Coastal structures, 2019
Large numbers of offshore wind turbines, near-shore bridges and port facilities are supported by ... more Large numbers of offshore wind turbines, near-shore bridges and port facilities are supported by driven piles. The design and installation of such piles is often problematic in Chalk, a low-density, porous, weak carbonate rock, which is present under large areas of NW Europe. There is little guidance available to designers on driveability, axial capacity, the lateral pile resistance which dominates offshore wind turbine monopile behaviour, or on how piles can sustain axial or lateral cyclic loading. This paper describes the ALPACA project which involves comprehensive field testing at a low-to-medium density chalk research test site. The project is developing new design guidance through comprehensive field testing and analysis combined with in-situ testing campaigns and advanced static-and-cyclic laboratory testing on high quality block and rotary core samples.
The recently-completed PISA (PIle Soil Analysis) research project aimed to improve the design of ... more The recently-completed PISA (PIle Soil Analysis) research project aimed to improve the design of monopile foundations for offshore wind turbines (OWT), focusing on laterally-loaded monopiles with length-to-diameter (L/D) ratios between 2 and 6. The project resulted in a novel one-dimensional (1D) design model which overcomes certain limitations in current practice. The PISA 1D design model facilitates rapid design calculations, based on the use of Timoshenko beam theory to represent the monopile. The soil response is modelled via soil reactions, applied along the shaft and at the base of the monopile. The soil reaction curves are determined using a series of three-dimensional (3D) finite element (FE) calibration calculations, performed prior to the design process, spanning a representative design space. A new software tool called PLAXIS MoDeTo (Monopile Design Tool) has been developed based on this design procedure. This design tool facilitates the automatic generation and calculati...
The PISA design model is a procedure for the analysis of monopile foundations for offshore wind t... more The PISA design model is a procedure for the analysis of monopile foundations for offshore wind turbine applications. This design model has been previously calibrated for homogeneous soils; this pa...
Tidal turbine blades are smaller than wind turbine blades yet carry similar bending moments. This... more Tidal turbine blades are smaller than wind turbine blades yet carry similar bending moments. This pro vides a structural challenge and limits how thin the blades can be made, which subsequently affects the hydrodynamic performance of the rotor. Thinner blades generally offer higher performance but require thicker laminates hence are more expensive to build. Opinions vary amongst tidal turbine developers as t o the best compromise for overall cost of energy. The parametric study presented in this paper includes a full structural and hydrodynamic design of a megawatt-sc ale axial flow tidal turbine rotor. Typical tidal turbine si te parameters are assumed in terms of flow speed, turbulence and wave loading based on Gurit's experience of several rotors of th is size. The blades are designed using epoxy composites in accor dance with industry best practice. The blade thickness, chord and twist distribution are varied to find the effect on annual energy production and blade manufactu...
Frontiers in Offshore Geotechnics III, 2015
ABSTRACT There is currently a significant focus on developing offshore wind power in the UK and E... more ABSTRACT There is currently a significant focus on developing offshore wind power in the UK and Europe. The most common foundation type for wind turbines is a single large diameter pile, termed a monopile, on which the turbine is located. As the diameter of such piles is envisaged to increase in future installations, there are concerns that current design methods are not applicable. To explore this problem, the joint industry project PISA has been established, with the aim to develop a new design framework for laterally loaded piles utilised in the offshore wind industry, based on new theoretical developments, numerical modelling and large scale field pile testing. This paper presents an overview of numerical modelling undertaken as part of the project.
Géotechnique Letters, 2015
In recent years, fibre Bragg grating (FBG) sensors have emerged as a relatively new strain sensin... more 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 bet...
Frontiers in Offshore Geotechnics III, 2015
Journal of Geotechnical and Geoenvironmental Engineering
This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress wav... more This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length-to-diameter ratios of 6∶20 were impact driven at an established chalk test site in Kent, United Kingdom. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles' responses under each hammer blow. A high-frequency (5 kHz) fiber optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared the time series of pile head PDA measurements and FBG strains measured below the ground surface. Numerical solutions of the one-dimensional wave equation were optimized by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high-resolution strain measurements are made.
Journal of Waterway, Port, Coastal, and Ocean Engineering
Géotechnique
Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations.... more Offshore wind turbines in shallow coastal waters are typically supported on monopile foundations. Although three-dimensional (3D) finite-element methods are available for the design of monopiles in this context, much of the routine design work is currently conducted using simplified one-dimensional (1D) models based on the p-y method. The p-y method was originally developed for the relatively large embedded length-to-diameter ratio (L/D) piles that are typically employed in offshore oil and gas structures. Concerns exist, however, that this analysis approach may not be appropriate for monopiles with the relatively low values of L/D that are typically adopted for offshore wind turbine structures. This paper describes a new 1D design model for monopile foundations; the model is specifically formulated for offshore wind turbine applications, although the general approach could be adopted for other applications. The model draws on the conventional p-y approach, but extends it to include additional components of soil reaction that act on the pile. The 1D model is calibrated using a set of bespoke 3D finite-element analyses of monopile performance, for pile characteristics and loading conditions that span a predefined design space. The calibrated 1D model provides results that match those obtained from the 3D finite-element calibration analysis, but at a fraction of the computational cost. Moreover, within the calibration space, the 1D model is capable of delivering high-fidelity computations of monopile performance that can be used directly for design purposes. This 1D modelling approach is demonstrated for monopiles installed in a stiff, overconsolidated glacial clay till with a typical North Sea strength and stiffness profile. Although the current form of the model has been developed for homogeneous soil and monotonic loading, it forms a basis from which extensions for soil layering and cyclic loading can be developed. The general approach can be applied to other foundation and soil-structure interaction problems, in which bespoke calibration of a simplified model can lead to more efficient design.
Volume 10: Ocean Renewable Energy
There are two approaches to extracting power from tides — either turbines are placed in areas of ... more There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as ex...
Revue Française de Géotechnique
Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. La... more Chalk is present under large areas of NW Europe as a low-density, porous, weak carbonate rock. Large numbers of offshore wind turbines, bridges and port facilities rely on piles driven in chalk. Current European practice assumes ultimate shaft resistances that appear low in comparison with the Chalk’s unconfined compression strength and CPT cone resistance ranges and can impact very significantly on project economics. Little guidance is available on pile driveability, set-up or lateral resistance in chalk, or on how piles driven in chalk can sustain axial or lateral cyclic loading. This paper describes the ALPACA (Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing) project funded by EPSRC and Industry that is developing new design guidance through comprehensive field testing at a well-characterised low-to-medium density test site, supported by analysis of other tests. Field experiments on 36 driven piles, sixteen of which employ high resolution f...