A Calculation Model of the Equilibrium Scour Depth for Monopile Foundations Under Waves and Currents

The erosive power of a free-falling high-velocity water jet, flowing from a dam spillway, could create a scour hole downstream of the dam, endangering the foundation of the dam. Despite extensive research since the 1950s, there is presently no universally agreed method to predict accurately the equilibrium scour depth caused by plunging jets at dams. These formulae yield a large range of equilibrium scour dimensions. The hydrodynamics of plunging jets and the subsequent scour of a rectangular, horizontal and vertical fissured rock bed were investigated in this study by means of a physical model. Equilibrium scour hole geometries for different fissured dimensions (simulated with rectangular concrete blocks tightly prepacked in a regular rectangular matrix), for a range of flow rates, plunge pool depths, and dam height scenarios were experimentally established with 31 model tests. From the results, non-dimensional formulae for the scour hole geometry were developed using multi-linear regression analysis. The scour depth results from this study were compared to various analytical methods found in literature. The equilibrium scour hole depth established in this study best agrees with that predicted by the Critical Pressure method.

Download Full-text

Experimental investigation of the equilibrium scour depth below submerged pipes both in live-bed and clear-water regimes under the wave effect

Applied Ocean Research ◽

10.1016/j.apor.2018.08.010 ◽

2018 ◽

Vol 80 ◽

pp. 49-56 ◽

Cited By ~ 2

Author(s):

Mustafa Dogan ◽

Aysegul Ozgenc Aksoy ◽

Yalcin Arisoy ◽

Mehmet Sukru Guney ◽

Vahid Abdi

Keyword(s):

Experimental Investigation ◽

Scour Depth ◽

Clear Water ◽

Wave Effect ◽

Water Regimes ◽

Equilibrium Scour Depth

Download Full-text

Scour around Spur Dike in Sand–Gravel Mixture Bed

Water ◽

10.3390/w11071417 ◽

2019 ◽

Vol 11 (7) ◽

pp. 1417 ◽

Cited By ~ 4

Author(s):

Manish Pandey ◽

Wei Haur Lam ◽

Yonggang Cui ◽

Mohammad Amir Khan ◽

Umesh Kumar Singh ◽

...

Keyword(s):

Water Depth ◽

Velocity Ratio ◽

Maximum Error ◽

Length Ratio ◽

Scour Depth ◽

Spur Dike ◽

Particle Ratio ◽

Cause Of Failure ◽

Equilibrium Scour Depth ◽

Sediment Mixture

Scour is the main cause of failure for spur dike. The accurate prediction of scour around spur dike is essential to design a spur dike. The present study focuses on the maximum scour depth in equilibrium condition and parameters, which influence it in a sand–gravel mixture bed. Outcomes of the present experimental study showed that the non-dimensional maximum equilibrium scour depth increases with critical velocity ratio (U/Uca), water depth-armour particle ratio (h/da), Froude number for sediment mixture (Frsm), water depth-spur dike length ratio (h/l), and decreases with increase in armour particle-spur dike length ratio (da/l). The maximum scour depth is proportional to dimensionless parameters of U/Uca, h/da, Frsm, h/l, but the scour depth is inverse proportional to da/l. Scour around spur dike in a sand–gravel mixture is mainly influenced by the property of the sediment mixture. The scour increases with decrease in non-uniformity of the sediment mixture. A non-linear empirical equation is proposed to estimate the maximum scour depth at an upstream nose of rectangular spur dike with a maximum error of 15%. The sensitivity analysis indicates that the maximum non-dimensional equilibrium scour depth depends on Frsm, followed by the secondary sensible parameters da/l, h/l, and h/da.

Download Full-text

Viscosity effects on local scour around vertical structures in clear-water conditions

E3S Web of Conferences ◽

10.1051/e3sconf/20184003038 ◽

2018 ◽

Vol 40 ◽

pp. 03038 ◽

Cited By ~ 1

Author(s):

Costantino Manes ◽

Francesco Coscarella ◽

Ashley Rogers ◽

Roberto Gaudio

Keyword(s):

Local Scour ◽

Hydraulic Structures ◽

Scour Depth ◽

Foundation Design ◽

Viscous Forces ◽

Erosion Rates ◽

Sediment Removal ◽

Viscosity Effects ◽

Horseshoe Vortices ◽

Equilibrium Scour Depth

Local scour represents the erosion process that occurs at the base of hydraulic structures overlying sediment beds. Horseshoe vortices forming at the bed-structure junction are the main responsible for sediment removal and dictate erosion rates as well as the maximum erosion depth resulting from a significant flow event. In steady-flow conditions this is often referred to as the equilibrium scour depth, which, for many hydraulic structures, represents a key parameter for foundation-design and risk-assessment purposes. The equilibrium scour depth has been investigated for decades and many predictive formulae have been developed following the classical empirical approach, whereby numerous experimental datasets are used to isolate and identify the influence of non-dimensional groups emerging from dimensional analysis. Within this context, the influence of obstacle Reynolds numbers, and consequently of viscous forces, has always been neglected because of the large Re values normally encountered in engineering and laboratory conditions. The present paper demonstrates that this assumption is largely incorrect especially for beds made of sand or finer material. The theoretical analysis presented in Manes and Brocchini ([1]) is herein extended to include viscosity effects and investigate their importance on equilibrium scour depths forming around obstacles resembling bridge piers.

Download Full-text

A numerical approach for determining equilibrium scour depth around a mono-pile due to steady currents

Applied Ocean Research ◽

10.1016/j.apor.2016.02.010 ◽

2016 ◽

Vol 57 ◽

pp. 114-124 ◽

Cited By ~ 7

Author(s):

A.L.J. Pang ◽

M. Skote ◽

S.Y. Lim ◽

J. Gullman-Strand ◽

N. Morgan

Keyword(s):

Numerical Approach ◽

Scour Depth ◽

Equilibrium Scour Depth

Download Full-text

Examination of Blockage Effects on the Progression of Local Scour around a Circular Cylinder

Water ◽

10.3390/w11122631 ◽

2019 ◽

Vol 11 (12) ◽

pp. 2631 ◽

Cited By ~ 2

Author(s):

Priscilla Williams ◽

Ram Balachandar ◽

Tirupati Bolisetti

Keyword(s):

Local Scour ◽

Estimation Methods ◽

Scour Depth ◽

Blockage Ratio ◽

Small Influence ◽

Channel Blockage ◽

Median Diameter ◽

Equilibrium Scour Depth ◽

Future Work

An evaluation of scour estimation methods has indicated that the effects of blockage ratio are neglected in both scour modelling and development of new predictive methods. The role of channel blockage on the mechanism and progression of local scour is not well understood, and further analysis is required in order to incorporate this effect into scour estimation. In the present investigation, local scour experiments were carried out under varying blockage ratio. The results were compared with data from literature in order to explore the effects of blockage ratio (D/b, where D is the pier diameter, and b is the channel width) on equilibrium scour depth (dse/D, where dse is the depth of scour at equilibrium). It was determined that D/b had a small influence on both dse/D and the progression of scour depth (ds/D) when relative coarseness D/d50 < 100 (where d50 is the median diameter of sediment), and that the influence appeared to be amplified when D/d50 > 100. The efficacy of scour estimation methods used to predict the progression of local scour was also dependent on D/d50. A method of scour estimation used to predict dse/D was evaluated, and it was similarly found to be particularly effective when D/d50 < 100. In future work, further experiments and analysis in the range of D/d50 > 100 are required in order to establish the role of D/b under prototype conditions and to refine existing scour estimation methods.

Download Full-text

Effect of Viscosity on the Equilibrium Scour Depth at Single Cylindrical Piers

Journal of Hydraulic Engineering ◽

10.1061/(asce)hy.1943-7900.0001102 ◽

2016 ◽

Vol 142 (3) ◽

pp. 06015022 ◽

Cited By ~ 6

Author(s):

Rui M. M. Lança ◽

Gonzalo Simarro ◽

Cristina M. S. Fael ◽

António H. Cardoso

Keyword(s):

Scour Depth ◽

Equilibrium Scour Depth

Download Full-text

Clear-water scour at bridge piers in fine and medium gravel beds

Canadian Journal of Civil Engineering ◽

10.1139/l05-022 ◽

2005 ◽

Vol 32 (4) ◽

pp. 775-781 ◽

Cited By ~ 14

Author(s):

Rajkumar V Raikar ◽

Subhasish Dey

Keyword(s):

Bridge Piers ◽

Geometric Standard Deviation ◽

Scour Depth ◽

Size Factor ◽

Clear Water ◽

Envelope Curve ◽

Gravel Beds ◽

Sediment Size ◽

Gravel Size ◽

Equilibrium Scour Depth

An experimental investigation on scour at circular and square piers in uniform and non-uniform gravels (fine and medium sizes) under clear-water scour at limiting stability of gravels is presented. From the experimental results, it is observed that the equilibrium scour depth increases with decrease in gravel size. The variation of equilibrium scour depth with gravel sizes departures considerably from that with sand sizes. Consequently, the resulting sediment size factors for gravels, obtained from envelope curve fitting, are significantly different from the existing sediment size factor for sands. The influence of gravel gradation on scour depth is also prominent in non-uniform gravels. The time scales to represent the time variation of scour depth in uniform and non-uniform gravels are determined. For uniform gravels, the non-dimensional time scale increases with increase in pier Froude number and gravel size, whereas for non-uniform gravels, it decreases with increase in geometric standard deviation of particle size distribution of gravels.Key words: bridge pier, gravel beds, scour, erosion, sediment transport, open channel flow, hydraulic engineering.

Download Full-text

Effect of Reynolds Number on Local Scour Around a Monopile in Steady Current

Volume 7A: Ocean Engineering ◽

10.1115/omae2019-96735 ◽

2019 ◽

Author(s):

Xiaofan Lou ◽

Kaibing Zhang ◽

Zhenhong Chen

Keyword(s):

Reynolds Number ◽

Time Scale ◽

Time History ◽

Local Scour ◽

Circular Cylinders ◽

Scour Depth ◽

Clear Water ◽

Number Range ◽

Steady Current ◽

Equilibrium Scour Depth

Abstract The effect of Reynolds number (Re) on the local scour around a monopile encountering steady current was investigated experimentally in a water flume. The experiment was performed using circular cylinders with different diameters under two different freestream velocities, covering both clear-water and live-bed scours and a Reynolds number range of approximately 9,000–60,000. The time-series of the scour depth was recorded during the whole scour process and the scour pit was scanned after the scour process reached equilibrium. Results are presented in terms of the equilibrium scour depth, the time-scale of the scour process and the three-dimensional scour profile at different Reynolds numbers. For both clear-water and live-bed scours, the time history of the scour process indicate that the time-scale becomes larger as Re increases. It is also found that the normalized equilibrium scour depth, as well as the normalized scour radius, decrease with the increasing Re. An empirical equation of the equilibrium scour depth is derived as a function of Reynolds number based on the experimental results so as to better account for Re effect in the scour design.

Download Full-text