Scour Countermeasures Research Articles

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.

Scour at Bridge Piers Protected by the Riprap Sloping Structure: A Review

Bridge piers on large rivers are often protected from scouring using launchable stone, such as a riprap sloping structure. While such scour countermeasures are effective for pier protection, they significantly alter flow conditions in the bridge opening by overtopping flow and flow contraction, deflecting the formation of the scour hole downstream and exposing the downstream riverbed to additional scour. This paper provides a comprehensive and relevant review of bridge scour estimation methods for piers with a riprap sloping structure installed as a scour countermeasure. Research on empirical methods for bridge scour estimation is reviewed and analyzed with formulae used for comparable structures—complex pier formulae and formulae for river training structures. A summary of relevant formulae applicable to piers with installed scour countermeasures is provided, as well as a discussion on the possible future research directions that could contribute to the field.

Using side flow jets as a scour countermeasure downstream of a sluice gate

BackgroundLocal scour is one of the main problems affecting the stability and operation of control hydraulic structures. Many techniques were used to control the resulting scour. In the recent study, a new technique was used to control local scour downstream single-gate hydraulic regulator by using side flow jets. This study aimed to demonstrate the effect of side jets at different angles on the local scour parameters (depth, length, and volume) and energy dissipation in the downstream hydraulic regulator.ResultsA physical model was used to represent the open channel, regulator, and the side jets with different angles. Five flow discharges, four jet angles, and three gate openings were applied through the experiment. The experiment results showed that the presence of side jets had a remarkable effect on the parameters of the local scour hole and energy dissipation. They dissipated more energy of hydraulic jump than in the absence of jets, and consequently, scour hole dimensions were significantly reduced. Regression analysis was used to deduce equations that can predict the development of local scour downstream sluice gate considering the inclination angle of side flow jets under different flow conditions.ConclusionsSide flow jets can be used as scour reducer techniques with the advantages of eliminating the jet clog produced from sediments and suspended solids.

Application of a Single Porous Basket as a Pier Scour Countermeasure

This paper presents a study on bridge pier protection with a single porous basket (SPB) in clear-water experiments. The SPB is a type of combined flow-altering countermeasure. The SPB was installed at a distance ahead of the protected pier. After a series of tests, the results showed that appropriate installation of the SPB was able to effectively adjust the flow pattern to reduce the down-flow motion and horseshoe vortex ahead of the pier. Dominant factors for the pier protection—considered for all tests—included the distance between the basket and pier, submerged depth of the basket, basket length, pier diameter, basket diameter, hole size, porosity, and the flow approaching angle. After evaluating these parameters through laboratory tests, the results of protection were optimized. In optimal conditions, the SPB was able to provide maximum pier protection and decrease the maximum scour depth by as much as 75.53%.

Lifetime Resilience Measurement of River-Crossing Bridges with Scour Countermeasures under Multiple Hazards

River-crossing bridges are often subject to multiple hazards, including foundation scour, seismic attacks, and environmental degradation. When river-crossing bridges are in service, they should be restored rapidly after any disruption over their lifetime. To achieve this resilient quality, it is necessary to assess the system resilience subjected to multihazard impacts and the beneficial effects of any retrofitting or hazard-countermeasure in a lifetime context. To river-crossing bridges, one important intervention is to implement scour countermeasures. This study presents a probabilistic framework to quantify the lifetime system resilience of river-crossing bridges subject to multiple hazards. Notably, the framework is designed to reveal how progressive and abrupt hazards interact and result in resilience degradation and how scour countermeasures contribute to resilience enhancement. Experimental outcomes reveal the positive and distinct effects of implementing scour countermeasures at different times. The proposed framework is expected to assist civil engineers in conducting lifecycle management of river-crossing bridges that are subject to hydraulic scour and demand timely countermeasures.

Migration of Maximum Scour Location around Wide Setback Bridge Abutments in Floodplains

AbstractLocation of maximum scour depth is a key feature for the accurate design of scour countermeasures. Experimental results show that the maximum scour depth around wide setback abutments migra...

Mitigation of Scour Failure Risk of a River Bridge Located in an Ungauged Basin

In this study, scour failure risk of the Çatalzeytin Bridge located in the Western Black Sea Basin, Turkey, was assessed for possible future flood events and appropriate scour countermeasures were considered based on economic and constructability considerations. Waterway adequacy in the spans of the bridge and scour criticality around bridge foundations considered for risk calculations in HYRISK were estimated by hydrological and hydraulic analyses of the watershed and stream. Since the watershed of the bridge is ungauged, geomorphological instantaneous unit hydrograph concept was adopted to estimate the peak discharges with various return periods to be used in hydraulic modelling. Monte Carlo simulation results indicated that most of the simulated peak discharges were in the 95% confidence interval. Hydraulic model results from HECRAS indicated that waterway adequacy and scour criticality were critical for discharges with 200 and 500-year return periods. Scour failure risk of the Çatalzeytin Bridge was classified as high and it was proposed to reduce the risk by constructing partially grouted riprap as the most feasible alternative that would consequently increase the expected lifespan of the bridge. Following this methodology, river bridges may be prioritized based on the risk analysis.

Dynamic morphology in a bridge-contracted compound channel during extreme floods: Effects of abutments, bed-forms and scour countermeasures

Fluvial morphology in compound river channels usually undergoes drastic variation during extreme floods due to scour and erosion processes. Those processes can be highly dynamic consisting of multiple elements (e.g. bed-form migration, bank erosion, riprap break-down, etc) that are inter-dependent. The existence of bridge abutments and embankments that lead to flow contraction on the floodplain brings more complexity and uncertainty. The present study investigated flood-related processes around bridge sites in a compound channel with different abutment/embankment configurations. Results show that a longer abutment/embankment pushes the high-shearing zone on the floodplain (around abutment toe) further towards the bank slope and causes a higher risk of undercutting at the toe area, while vertical flow pressurization had a more significant effect on enhancing general bed shearing. The main channel bank tends to retain a constant slope (2:1) as scour progresses gradually during floods. The channel bed scour is closely related to the unit discharge contraction ratio determined by both lateral and vertical flow contractions. Regarding the interaction between dynamic processes, migrating bed-forms enhanced sediment erosion by cyclic “embedment–winnowing” processes when they met destabilized loose riprap rocks. Thus, rocks sliding into the main channel may cause a higher risk of bed subsidence and then embankment failure. In total, four bed-form migration types (i.e. interaction types) are observed for different abutment/embankment lengths and flow intensities. In general, the observed processes provide a clear picture of how channel morphology is altered dynamically by multiple factors during extreme floods. Additionally, the findings in this study are integrated under a framework to evaluate the potential scour and erosion hazards in a real river section. It is found that those hazards may go beyond individual sites, affecting each other and then the morphological evolution at a catchment scale. A more comprehensive study in the future will enable this framework to performed more quantitative analysis.

Potential of Epoxidised Natural Rubber Alumina Nanoparticles (ENRAN) sheet as local bridge pier scour countermeasure

This study attempts to reduce scour depth due to localised scour around a bridge pier by introducing Epoxidised Natural Rubber Alumina Nanoparticles (ENRAN) sheet acting as bridge pier sheathing. The performance of the ENRAN sheet was assessed based on the configuration of slots and by roughening with 1 cm diameter spheres. Experiments were conducted with pier shapes of cylindrical, square, and rectangular using a fixed sediment bed with median grain size (600 µm). Coarser slot spatial arrangement is more efficient in reducing 17% scour depth (from the non-sheathed pier), whereas closer placement of the roughened element has better performance up to 27%. Experiments were extended to investigate the combined slotted-roughened configuration, where higher scour reduction (35%) was observed, even for a rectangular shape. Not only the flexibility of the ENRAN sheet allows for installation for any pier shape, but also it’s durable characteristics proved ENRAN as an attractive method, providing self-protection to the bridge pier to minimise scouring.

Reducing Bridge Pier Scour Using Gabion Mattresses Filled with Recycled and Alternative Materials

Scour is caused by the erosive action of flowing water, which causes materials from the bed and the banks of a river to be moved or unsettled. Hydraulic structures can be drastically impacted as a result of scour, which is why it is one of the most common causes of bridge failure around the world. With a predicted increase in climate conditions, the subsequent failure of hydraulic structures due to scour is likely to proliferate as the flooding of waterways is projected to rise. This study aims to determine the viability of introducing alternative materials to a scour countermeasure used in construction—gabion models—in a bid to improve the sustainability of a project whilst providing suitable scour mitigation measures. Existing literature was examined to comprehend the different scour countermeasures used, as well as the use of alternative materials that can be used as a scour countermeasure. A laboratory experiment was then carried out using a bridge pier embedded in a flume channel protected by gabion mattresses filled with alternative materials—stone, clothing and plastic—to analyse their effectiveness. The results demonstrate that stone filled gabions are most effective at reducing bridge pier scour. However, recycled clothing as a gabion fill could prove to be a viable alternative in construction projects, potentially leading to reduced construction costs and greater sustainability. However, more research on a greater scale is required to test this thesis.

Application of endurance time method to seismic fragility evaluation of highway bridges considering scour effect

Earthquake and flood scour are two main causes of failures to highway bridges. This study developed an alternative fragility analysis framework of bridges based on endurance time method (ETM). A two-span reinforced concrete highway bridge supported by three types of substructures, e.g. shaft foundation, two-column bent foundation and pile group foundation, was taken as the example bridge. The developed framework was used to obtain the fragility curves of the example bridges. The influences of scour depth, substructure design, ground motion direction and scour countermeasure on the seismic fragility of bridges were investigated. The developed seismic fragility analysis framework based on endurance time method yields accurate and efficient calculation compared with IDA method. Scour reduces the bearing capacity of the foundation and affects the seismic fragility of bridges. However, the effect of scour on the seismic fragility varies with the bridge substructure design, the ground motion direction and the application of the scour countermeasure.

Sacrificial Piles as Scour Countermeasures in River Bridges A Numerical Study using FLOW-3D

Scour is defined as the erosive action of flowing water, as well as the excavating and carrying away materials from beds and banks of streams, and from the vicinity of bridge foundations, which is one of the main causes of river bridge failures. In the present study, implementing a numerical approach, and using the FLOW-3D model that works based on the finite volume method (FVM), the applicability of using sacrificial piles in different configurations in front of a bridge pier as countermeasures against scouring is investigated. In this regard, the numerical model was calibrated based on an experimental study on scouring around an unprotected circular river bridge pier. In simulations, the bridge pier and sacrificial piles were circular, and the riverbed was sandy. In all scenarios, the flow rate was constant and equal to 45 L/s. Furthermore, one to five sacrificial piles were placed in front of the pier in different locations for each scenario. Implementation of the sacrificial piles proved to be effective in substantially reducing the scour depths. The results showed that although scouring occurred in the entire area around the pier, the maximum and minimum scour depths were observed on the sides (using three sacrificial piles located upstream, at three and five times the pier diameter) and in the back (using five sacrificial piles located upstream, at four, six, and eight times the pier diameter) of the pier. Moreover, among scenarios where single piles were installed in front of the pier, installing them at a distance of five times the pier diameter was more effective in reducing scour depths. For other scenarios, in which three piles and five piles were installed, distances of six and four times the pier diameter for the three piles scenario, and four, six, and eight times the pier diameter for the five piles scenario were most effective.

Scour reduction in sand beds against vertical jets by applying sheet-like countermeasures

The scour observed at the landside ground behind coastal protection facilities, such as seawalls and coastal dikes, due to tsunami overflows is the main reason for failures in such constructions. In this study, we focused on sheet-like (two-dimensional) scour countermeasures, which do not require large-scale excavation of the ground, and experimentally verified the effects of geonet and mesh sheets. By applying a vertical jet directly on the ground and increasing the external force, a situation close to the real scale conditions was reproduced. The experimental results show that the geonet material is able to significantly reduce the scour depth on both non-liquefied and liquefied grounds. We show that in the most effective case, the maximum pore-water pressure and the scour depth are reduced by about 91% and 86%, respectively, by the mesh sheet on the sand-bed surface.

Emergency scour repairs and performance at the Route 37 viaducts, NJ, USA

Route 37 links the New Jersey (USA) mainland to beach communities in Seaside Heights and is an emergency evacuation route. Carrying three lanes of traffic in each direction, the adjacent bridges are approximately 4900 ft (1490 m) long. Following the devastation of Superstorm Sandy in 2012, a special underwater inspection revealed severe scour damage at 23 piers, necessitating emergency scour countermeasures. The worst location suffered 15 ft (4·6 m) of local scour with 10 ft (3 m) of timber pile exposure. A fast-track inspection, analysis and design, expedited client responses, continuous coordination and excellent team cooperation achieved timely repairs to the worst-affected locations, while keeping the bridges open for much-needed access to the barrier island for storm recovery efforts. Emergency repairs included installation of grout-filled fabric formed bags installed in situ around the pile caps as formwork and filling voids beneath the caps with grout. Precast solid armouring blocks were then installed around the toe of the grout bags. These repairs preserved not only the most severely undermined piers, but also provided a resilient, long-term repair. Recent underwater inspections verified the effectiveness of the repairs, which have encouraged material deposition and replenished the natural bay bottom.

Six legged concrete (SLC) elements as scour countermeasures at wing wall bridge abutments

ABSTRACT Previous research studies have shown that abutment scour makes a major contribution to bridge failures. Protecting bridges against scour is, therefore, a priority need. For existing bridges, armouring methods, such as riprap, have a wide application. In the areas where providing stones is expensive, concrete blocks or similar techniques are often used. In the present study, the application of the Six Legged Concrete (SLC) elements was experimentally investigated. The SLC elements were placed in three different densities (open, medium and dense) at three different placement depths (h/l = 0, 0.5 and 1; where h is the element installation height above the bed and l is element height). Each alternative was tested under different flow conditions for a wing-wall abutment. In general, the results showed that the SLC elements can considerably reduce the scour under different flow conditions. In an optimal arrangement, the elements reduced the scour depth at abutment nose up to 100%. The maximum reduction of scour depth was obtained when the SLC elements were placed densely on the bed (h/l = 1).

Control of bed scour downstream of ski-jump spillway by combination of six-legged concrete elements and riprap

Local scouring is one of the key issues at the downstream of ski-jump spillways which may result in failure of the hydraulic structures. Therefore, adopting some measures in order to control and reduce this phenomenon is very crucial. In the present study, the effect of a special shaped element referred to six-legged concrete (SLC) elements along with riprap materials at the downstream of a ski-jump spillway as the scour countermeasure was experimentally evaluated. Experiments were conducted in unprotected (baseline tests) and protected bed (armed with SLC elements of the fixed size and two sizes of riprap with mean diameters of 9 and 20 mm) at five different flow discharges, with Froude numbers ranged from 3.42 to 15.51, and three tail-water depths. The results of baseline tests showed that increasing the flow discharge at different tail-water depths increased the maximum scour depth. Also, at each state, with the increase in the stability number, the maximum scour depth increases. From the results of the protected bed tests, it was concluded that with the application of SLC elements the jet penetrated from the pores between the protected cover and scour was developed, eventually resulting in the collapse of the protected layer. In addition, when the bed was protected by the combination of SLC elements and proper riprap size, the maximum scour depth beneath the protected material was reduced by 56.6%−100%. Using the experimental data, several empirical relations were developed to predict the maximum scour depth for different protection alternatives under different conditions. By defining the bed scour as a criterion for the stability of SLC, a design graph was also proposed to determine the required riprap size.

Local scour at a complex pier with inclined columns footed on capped piles: effect of the pile arrangement and of the cap thickness and elevation

ABSTRACT Experiments were performed for local scour at a complex pier with two inclined, rectangular columns footed on a group of circular piles with a pile cap. The research fills a gap in existing literature, where studies for complex piers have considered a single, vertical column. The laboratory campaign involved the variation of the pile diameter and arrangement, and of the cap thickness and elevation above the non-scoured bed. The results of carefully conducted scour runs revealed the cap elevation as a most influential parameter. In cases of buried and partially buried pile cap, in fact, the cap acted as a scour countermeasure. For high cap elevation, the supporting piles were also exposed to the flow and their size influenced the resulting scour depth values as it directly impacted on the pier frontal area. The measured scour depth was compared to the values predicted by several literature methods for complex piers with a vertical column, supporting the possibility to extend their use to the geometry investigated in the present study.

Sensitivity of river sediment transport and bridge scour to effects of flow, temperature, and sea level

AbstractSediment transport has implications for activities such as fishing, flood control, scour countermeasures, and dredging through altered flow depths and sediment transport, bank erosion, and bridge scour. To estimate the changes in sediment transport and bridge scour, river discharge, water surface slope, water temperature, and tailwater depth (to simulate sea‐level rise) were altered in existing sediment transport and scour models. It was found that (a) in uniform flow upstream of sea‐level rise effects, sediment transport is sensitive to discharge but not to temperature; (b) in non‐uniform flow affected by sea‐level rise, sediment transport is sensitive to water surface slope and discharge but not to temperature; (3) the discharge value to restore the sediment transport rate existing before sea‐level rise is proportional to the water surface slope ratio to the fourth power; (4) the discharge value to restore the bed sediment size existing before sea‐level rise is proportional to the water surface slope ratio to the three‐fourth power; (5) abutment scour is weakly inversely proportional to the water surface slope but more strongly proportional to the discharge in a logarithmic relation; (6) pier scour is weakly proportional to the water surface slope but more strongly proportional to the discharge in a logarithmic relation; and (7) the discharge to restore both abutment and pier scour depths to their original values prior to sea‐level rise is proportional to the water surface slope ratio to the 9/25th power. Full equations for each of these relationships are given in the article. These relationships can be used for future application and planning purposes.

Combined solutions to reduce scour around complex foundations: an experimental study

In this study, the simultaneous application of sacrificial piles and cable was experimentally examined as a pier scour countermeasure. The experiments were carried out for a single pier, a group of two and three piers using a clear-water regime. It is believed that applying the sacrificial piles and cable at the same time decreases the scour depth at a single pier and a group of two piers efficiently. In a group of three piers, the sacrificial piles with triangular configuration were able to decrease the scour depth considerably with a value of 69% reduction at the first pier. Nevertheless, the cable affects the scour depth reduction negatively at the group of three piers. This research highlights that the combination of cable and sacrificial piles is a suitable method to decrease the local scour at a single and a group of two piers, while sacrificial piles alone can be highly recommended for the group of three piers.