Scour Protection Research Articles

Numerical study on local scour characteristics of multi-bucket jacket foundation considering exposed height

At present, offshore wind farms around the world have successively applied Multi-Bucket Jacket Foundations (MBJF), but little research has been done on the scour characteristics of MBJF. In this study, a three-dimensional numerical model is established to study the scour characteristics of large-diameter, wide-shallow, and multi-bucket foundations in deep water areas. The simulation results of the single pile foundation erosion based on this model are in good agreement with the existing experimental results. Also, an optimized grid division strategy is proposed based on a large number of comparative analyses, discussing the influence on the flow field, the bed elevation contour, and the scouring depth under different exposed height(h), bucket diameter(D), and bucket spacing(d) of the MBJF. Then, the influence of the upper structure on the scour characteristics is quantified. The results show that two sides of the buckets can form scoop-shaped scour holes with steep front and gentle back, with deposition of sand formed on the front and back sides. As the exposed height increases, the scouring depth initially shows an increasing trend, which then decreases. The scouring depth of the front row buckets decreases as the diameter increases, while it increases as the diameter for the rear row buckets increases. Compared with d=1.5D and d=3D, d=2D has the smallest scouring depth. Within the normal scale range, the maximum deviation coefficient of the influence of the upper jacket structure on the foundation scouring depth does not exceed 5.2%. Finally, based on V(velocity), H (water depth), μ (viscosity) the basic flow variables, the scouring prediction formula based on dimensionless parameters is obtained. The findings can be used to provide a reference for the design and scour protection of MBJF.

Scour Protection of Submarine Pipelines Using Ionic Soil Stabilizer Solidified Soil

A novel scour protection approach for pipeline using the Ionic Soil Stabilizer (ISS) solidified soil was proposed in this study. The ISS-solidified slurry can be poured adjacent to the pipeline immediately after it was placed, or in the growing scour holes. In the present study, the first type was utilized as the scour protection layer around the pipeline. A series of laboratory flume tests were conducted to validate the protective capacity of ISS-solidified slurry for the pipeline in waves and combined waves and current. Then, the scanning electron microscope (SEM) tests and pore size tests were carried out, respectively, to investigate the mechanism of ISS-solidified slurry for scour protection around the pipeline. Finally, the effects of the ISS-solidified layer for liquefaction stability of non-cohesive subsoil were evaluated. The results indicated that the ISS-solidified slurry is a reliable, economic approach for scour protection around pipelines in the ocean environment. It is noteworthy that if a non-cohesive soil layer underlies the ISS-solidified slurry, it is vulnerable to suffer accumulated liquefaction due to the dense crust structure of the ISS-solidified layer, so the adverse effects for accumulated liquefaction should be considered carefully due to the set of the ISS-solidified layer.

Countermeasures for local scour at offshore wind turbine monopile foundations: A review

Local scour at monopile foundations of offshore wind turbines is one of the most critical structural stability issues. This article reviews the contemporary methods of scour countermeasures at monopile foundations. These methods include armouring countermeasures (e.g., riprap protection) to enhance the anti-scour ability of the bed materials and flow-altering countermeasures (e.g., collars and sacrificial piles) to reduce downflow or change flow patterns around the monopiles. Stability number and size-selection equations for riprap armour layers are summarised and compared. Moreover, other alternative methods to riprap are briefly introduced and presented. A typical graph of the scour depth reduction with different collar sizes and elevations under specific test conditions is summarised and compared with a plot for a pile founded on a caisson. Reduction rates for different flow-altering countermeasures, including the collar, are listed and compared. A newly developed soil improvement method, namely microbially induced calcite precipitation (MICP), is also reviewed and introduced as a scour protection method. As a popular bio-soil treatment method, MICP has a good potential as a scour countermeasure method. Bio-soil treatment methods and traditional armouring methods are defined as active and passive soil enhancement scour countermeasures, respectively.

Solidification sludge as a scour countermeasure in ocean engineering

This paper presents a new solidification sludge method to overcome the shortcomings of scour protection in ocean engineering. A series of experiments are carried out to investigate the effects of solidification sludge components on the viscosity and scour resistance velocity. The results reveal that the values of viscosity and scour resistance velocity are exponential functions with cure time. The scour resistance velocity can be estimated by viscosity, and the scour resistance velocity is found to be a power function with viscosity with high correlation coefficient. Adding the dosages of cement, HPMC and sodium silicate, reducing the water content and raising the temperature are effective ways to improve the anti-scouring ability of solidification sludge in ocean engineering. The bigger the pile diameter, the higher the anti-scouring ability.

Influence of scour protection layers on the lateral response of monopile in dense sand

The scour protection layers are usually installed around the monopiles to prevent the formation of scour hole. While extensive studies have been performed on the effectiveness of scour protection layer as mitigation measure, no study to date has been found to quantify the influence of scour protection layer on the lateral response of monopiles. In this study, centrifuge tests and numerical analyses were performed to examine explicitly the influence of the scour protection layer on the monopile response under lateral load in sand. It was found that a scour protection layer with a diameter of 5 times the diameter of the monopile (5D) and equivalent surcharge pressure of 15 kPa can increase the foundation lateral capacity by more than 30% and significantly decrease the accumulation of deflection by more than 100% in dense sand. Numerical analyses suggested that the beneficial contribution is attributed to the densification of sand and the increase of effective stress around the pile, which increased the stiffness and ultimate resistance of the soil reaction curve (i.e., p-y curve). Numerical parametric studies suggested that the beneficial effect of scour protection layer is also applicable to monopile in loose sand and by considering the contribution of the scour protection layer, the embedment length of the monopile can be reduced by 10%.

Performance Evaluation of Scour Protection around a Bridge Pier through Experimental Approach

Performance Evaluation of Scour Protection around a Bridge Pier through Experimental Approach

Entrainment of Sediment Particles in Protection Layers

AbstractProtection layers are often used to prevent scour and erosion, e.g., prevention of scour around wind turbine foundations. However, several cases exist where installed scour protection has s...

Numerical computation of fluid–solid mixture flow using the SPH–VCPM–DEM method

In this paper, a unified particle-based solver is developed to solve complex fluid–solid​ mixture flow problem involving many elastic solid bodies. Our previous Fluid Structure Interaction (FSI) solver that incorporates Smoothed Particle Hydrodynamics (SPH) for fluid modelling and Volume Compensated Particle Method (VCPM) for elastic solid modelling is extended by incorporating the Discrete Element Method (DEM) for modelling the contact force between colliding elastic solid bodies. The contact force is modelled using the non-linear Hertzian formulation. The method is firstly validated by solving several benchmark FSI problems that involve only one solid body. Then, solid–solid interaction is modelled and the collision problem involving two elastic rings and the well-known Drafting, Kissing and Tumbling (DKT) phenomenon in a fluid domain are simulated. The results agree considerably well with other benchmark numerical solutions. The collapse of Aluminium cylinder layers (in dry and wet conditions) is then simulated and it is found that the numerical result is comparable to the experimental data. Following that, the SPH–VCPM–DEM method is used to solve a more complex problem involving the dumping of solid objects through solid and perforated fall pipes for scour protection. The results show the potential of the SPH–VCPM–DEM method in simulating complex fluid–solid mixture flow.

New UK guidance on hydraulic actions on highway structures and bridges

This paper outlines key technical changes introduced to two documents in Highways England Design Manual for Roads and Bridges that cover hydraulic actions on structures: CD 356 and CS 469. CD356 provides practical requirements and guidance for designers to determine hydraulic actions that are either not covered or are covered in insufficient detail in the Eurocodes and UK national annexes, and incorporates provisions for climate change. These include design processes, scour assessment, scour protection design, methods for deriving input parameters, and site investigation. CS 469 provides practical requirements and guidance for the inspectors, assessors and asset managers of structures. Its new extended scope includes structures over or adjacent to water, on floodplains and located where significant surface water flooding has occurred. The document includes requirements and advice on scour caused by floating or submerged debris, other hydraulic actions, scour emergency inspections and scour management of risk, with amendments to scour risk scores and ratings. Climate change allowances are updated. It clarifies where the advice of the overseeing organisation is needed, roles and responsibilities of key stakeholders in the scour inspection, assessment and risk management process, the definition of a competent civil or structural engineer and many of the technical definitions.

Using nanomaterial to minimize the local scour downstream of sluice gate

Prediction of scour depths is an important aspect related to the overall stability of hydraulic structures. In this research, small-scale laboratory experiments were carried out to explore the effectiveness of mixing different percentages of Nanomaterial (Silica fume) to non-cohesive (alluvial) movable bed soil to develop mixture of bed material with significant characteristics to minimize the local scour caused by high-velocity jets downstream of a sluice gate. The experiments were executed employing 9 jet Froude numbers ranged from 1.88 to 2.81 associated with 3 heights for gate opening, and 3 tailwater depths. The bed material has 5 different percentages of Silica fume mixed by weight and 2 types of mixing with and without water were used. Ninety-nine experiments were conducted, out of which 9 experiments were done using fine sand as a bed material for the referenced cases. Graphical relationships were presented for maximum scouring and silting depths for different hydraulic conditions and bed materials. This research demonstrated that the type of mix (dry-mix or wet-mix) had a significant influence on the geometry of scouring and silting for the same flow conditions and the mixed percentage ratio of Silica fume. For dry-mix, the scouring and silting depths increased as the percentage ratio of Silica fume increased. While for wet-mix, the scouring and silting depths decreased as the percentage ratio of Silica fume increased. Also, the wet-mix effectively reduced the local scour volumes by 34.65% and 83.05% and decreased the silting volumes by 33.35% and 89.42% according to the percentage of Silica fume. Using a bed mixture of 8% Silica fume wet-mix showed 83.05% and 89.42% decrease in scouring and silting volumes, respectively, compared to pure fine sand bed material. From practical and financial aspects, the presented composition of bed material can effectively replace the smooth apron or at least decrease its length to reduce the construction cost. The obtained results present an untraditional technique for local scour protection downstream hydraulic structures.

Apron and Cutoff Wall Scour Protection for Piano Key Weirs

Piano key (PK) weirs are used in a variety of flow control structure applications, including spillway crests and open channel diversion structures. However, to the best of authors’ knowledge, structure-specific design guidance for scour mitigation is still needed. To fill this gap of knowledge, a systematic experimental campaign was conducted by testing different configurations of horizontal aprons with a cutoff wall. Protection structures were located at the toe of the PK weir. Namely, experiments were performed at large-scale to assess the effect of three apron lengths on downstream scour hole geometry under different hydraulic conditions. It was observed that a horizontal apron deflects the plunging jets originating from the PK weir, thus significantly reducing scour. Experimental evidence allowed corroboration that significant scour depth reduction occurs for an apron length 1.5 times the weir height, with longer aprons found to provide marginal benefits. Finally, also provided herein are tools to estimate the main scour characteristics and help practitioners in optimizing apron design.

Effect of frequency of minute-amplitude oscillatory shear loadings on ultimate yield stress of cohesive sediments

The ultimate yield stress of cohesive sediments changes with oscillatory loading or vibration. Given a strong enough vibration, the sediment may be fluidized. In this study, the effect of the frequency of minute-amplitude oscillatory shear loadings on the ultimate yield stress of cohesive sediments was experimentally and analytically investigated in a laboratory. The test samples were prepared with cohesive sediments with a median particle size of 31 μm and at four water content (31.8% to 37.03%). The sediments were subjected to continuous oscillatory shear loadings with a constant frequency (0–131.6 Hz). The findings of the study indicated that the ultimate yield stress of cohesive sediments under minute-amplitude oscillatory shear loadings was dependent on the oscillatory shear frequency, water content, and the ultimate yield stress of the sediments prior to the application of the oscillatory shear loading. This study revealed that there exists a critical shear loading frequency fcr. When the oscillatory shear frequency (f) was less than the critical shear frequency (fcr), the ultimate yield stress decreased as f increased. However, when f was greater than fcr, the ultimate yield stress was constant, irrespective of further increase of the oscillatory shear frequency. The former condition is identified as the non-equilibrium fluidization stage and the latter, the equilibrium fluidization stage. The fcr value decreased as the water content increased. In the equilibrium fluidization stage, the dimensionless yield stress Su/Su0 did not vary with the water content or oscillatory shear frequency. Two discrete formulae were proposed to estimate the ultimate yield stress of cohesive sediments subjected to minute-amplitude oscillatory shear loadings for the non-equilibrium and equilibrium fluidization stages. To explore the engineering applications of the formula for the equilibrium fluidization stage, a series of vertical pull out tests were performed using a dynamic torpedo anchor. This study provides an important method for distinguishing the degree of fluidization and sheds lights on potential applications in coastal and marine engineering, such as pile or anchor installation and extraction and scour protection in cohesive bed.

The variability of marine sediment erodibility with depth: Centimetric scale effects detected from portable erosion flume tests

A portable erosion flume has been developed that is capable of estimating erosion threshold and erosion rate relationships for fine-grained specimens over the depth of a typical sample tube. This newly-designed apparatus is a recirculating flume capable of generating steady currents over the exposed section of the sample. In this paper, the erosion properties of two marine sediments have been determined and show a significant systematic variation with depth at centimetre scale that would have implications for the potential need for scour protection engineering. The tests showed that the critical erosion onset velocity doubled over the upper 200 mm of each sample, and the erosion rate fell by an order of magnitude. The increased erosion resistance with depth is consistent with the general trend of erodibility reducing with decreasing moisture content. Ignoring this depth effect when selecting design values of the erosion properties could lead to erroneous predictions of scour rate and extent around subsea structures, and unnecessary scour protection engineering costs.

Experimental Evaluation of Dynamic Rock Scour Protection in Morphodynamic Environments for Offshore Wind Jackets

Bottom-fixed offshore wind turbines are generally built on continental-shelf sections that are morphodynamically active due to their shallow depths and severe wave and current conditions. Such sites are commonly protected against scour to prevent the loss of structural stability. Scour protection can be designed using static or dynamic solutions. Designing dynamic protection requires experimental validation, especially for singular or unconventional structures. This article presents an experimental method for the laboratory analysis of scour protection for jacket foundations placed at morphodynamically active sites. The test campaign was conducted within the project East Anglia ONE (UK) as part of the asset owner studies and aimed to evaluate operation and maintenance (O&M) aspects, independent of the contractor’s original design assessments. The physical experiments explored morphodynamic changes on the sea bottom and their importance to scour protection, as well as the importance of the history of the wave loads to the deformation of the rock scour protection. This was explored by repeating different cumulative tests, including a succession of randomly ordered sea states (Return Period (RP) 1-10-20-50 years). The experimental results show that the deformation of the rock sour protection was the greatest when the most energetic sea states occurred at the beginning of the experimental test campaign. The maximum deformation was at 5D50 when the first test was also the most energetic, while it was at 3D50 when not included as the first test, yielding a 40% reduction in the scour protection deformation.

Bridge Failure Prevention: An Overview of Self-Protected Pier as Flow Altering Countermeasures for Scour Protection

The inherent scour process around the bridge piers needs to be considered and crucial to ensure a sustainable and economical bridge design. The performance of any scour protection/controlling devices around bridge piers is determined on how each device counters or minimize the scouring process. Besides the usually adopted bed armouring, abundant studies have been conducted to evaluate the efficiency of flow-altering countermeasures in reducing local scour depth. The flow changes due to the rigid pier are modified in a way to reduce the impinging effect on the bed. This paper discusses on the performance and feasibility of self-protected piers, defined as a pier without any additional structure built either next to or at a distance away from the pier. We paid attention to the efficiency of the proposed countermeasures in terms of possible maximum scour reduction and provide the best configuration of each self-protection pier. This review consists of analysis on the openings on pier including internal tubing, slot and pier groups, and modified pier shapes as the flow-altering, self-protected countermeasure alternatives.

Scour protections of collar around a monopile foundation in steady current

An experimental study on scour protection around a monopile foundation in steady current was carried out with the adoption of collar base and collar column. Through the analysis of scouring features, the effectiveness of the collar base and collar column on the local scour was quantified. The parameters of flow conditions (θs/θcr), diameter (Dp/D), and thickness (hs/D), together with the initial buried depth (xb/D) for the collar base and collar column were investigated. For the collar base, the increase in thickness would effectively prevent the local scour beneath the base and lead to a decrease in the critical value of Dp/D. The influence of the diameter Dp/D can be ascribed to the fact that the collar base can take over the seabed region that the horseshoe vortex governs and further reduce the sediment transport at the junction. As for the collar column, the existence of the initial buried depth xb/D would provide space for the local scour to develop. At a large value of initial buried depth, the diameter Dp/D is no longer the main physical parameter. The effectiveness of the collar base and collar column is independent of the flow intensity in live-bed conditions.

Quantification of Measurement and Model Effects in Monopile Foundation Scour Protection Experiments

The present work introduces an analysis of the measurement and model effects that exist in monopile scour protection experiments with repeated small scale tests. The damage erosion is calculated using the three dimensional global damage number S3D and subarea damage number S3D,i. Results show that the standard deviation of the global damage number σ(S3D)=0.257 and is approximately 20% of the mean S3D, and the standard deviation of the subarea damage number σ(S3D,i)=0.42 which can be up to 33% of the mean S3D. The irreproducible maximum wave height, chaotic flow field and non-repeatable armour layer construction are regarded as the main reasons for the occurrence of strong model effects. The measurement effects are limited to σ(S3D)=0.039 and σ(S3D,i)=0.083, which are minor compared to the model effects.

Scour protection assessment of monopile foundation design for offshore wind turbines

The driven monopile is the most common foundation type for all installed offshore wind turbines. These monopiles are often subject to scour phenomena, which cause a reduction in foundation strength and stiffness. In order to prevent the consequences of this phenomenon, scour protection systems are used to protect the seabed around a monopile structure against scour in practice. This paper presents a numerical model to investigate the effect of scour protection on the natural frequency and lateral responses of monopile-supported offshore wind turbines under the ultimate limit state (ULS), serviceability limit state (SLS) and fatigue limit state (FLS).This numerical model was validated through a series of model tests, and then applied to the National Renewable Energy Laboratory (NREL) 5-MW offshore wind turbine supported on an Offshore Code Comparison Collaboration (OC3) monopile with riprap rock scour protection system. The study concludes that the scour protection has a slight impact on the first natural frequency and monopile behavior under ULS and FLS. However, the scour protection significantly decreases the pile head rotation at mudline under SLS, which provides the opportunity for further optimization of monopile design by incorporating the contribution of scour protection, thereby leading to a more economical design.

I-RIPRAP Computer Vision Software for Automated Size and Shape Characterization of Riprap in Stockpile Images

Riprap rocks and large-sized aggregates have been used extensively in geotechnical and hydraulic engineering applications to serve as a key component for erosion/sediment control and scour protection. Toward sustainable and reliable use of riprap rocks, an efficient and accurate method to characterize the size and shape properties is deemed necessary. Current state-of-the-practice methods mostly assess riprap properties with labor-intensive and time-consuming inspection routines that involve manual size and weight measurements. Recent advances in the field of computer vision have been leveraged in this paper to apply deep learning for the development of an innovative image analysis tool for quantitative and efficient riprap characterization. Based on the single-aggregate and stockpile-aggregates studies conducted on this topic, this paper introduces a newly developed computer program, named I-RIPRAP, for the advanced characterization of aggregate size and shape from images of riprap stockpile(s). The essential features and software workflow, as well as the function and mechanism of each module, are described and discussed in detail. In addition to the deep learning methods for segmentation, I-RIPRAP also improves the morphological analyses with a volume/weight estimation module and a riprap category reference module to generate useful results that can facilitate quality assurance/quality control tasks. The I-RIPRAP software is envisioned to serve as an efficient and innovative tool for field and in-place evaluations of riprap and large-sized aggregates.

Scour Protections for Offshore Foundations of Marine Energy Harvesting Technologies: A Review

The offshore wind is the sector of marine renewable energy with the highest commercial development at present. The margin to optimise offshore wind foundations is considerable, thus attracting both the scientific and the industrial community. Due to the complexity of the marine environment, the foundation of an offshore wind turbine represents a considerable portion of the overall investment. An important part of the foundation’s costs relates to the scour protections, which prevent scour effects that can lead the structure to reach the ultimate and service limit states. Presently, the advances in scour protections design and its optimisation for marine environments face many challenges, and the latest findings are often bounded by stakeholder’s strict confidential policies. Therefore, this paper provides a broad overview of the latest improvements acquired on this topic, which would otherwise be difficult to obtain by the scientific and general professional community. In addition, this paper summarises the key challenges and recent advances related to offshore wind turbine scour protections. Knowledge gaps, recent findings and prospective research goals are critically analysed, including the study of potential synergies with other marine renewable energy technologies, as wave and tidal energy. This research shows that scour protections are a field of study quite challenging and still with numerous questions to be answered. Thus, optimisation of scour protections in the marine environment represents a meaningful opportunity to further increase the competitiveness of marine renewable energies.