Estimation Of Maximum Scour Depth Research Articles

Evaluation of angled splitters as scour countermeasure at circular piers

Scour around bridge piers is local phenomenon may cause complete failure for the hydraulic structure. This study explored experimentally using splitter plates at specific angles installed upstream single circular bridge pier to improve the nearby flow field and minimize the local scour. Ninety runs were carried out considering 9 splitter models. Four splitter lengths and 3 vertex angles were used. The splitter lengths were between 0 and 1.5 times of pier diameter, each was tested for 3 vertex angles ranged between 0° and 30°. The tests were done under 9 different hydraulic conditions including 3 discharges of 75, 100, and 125 l/s and 3 tailwater depths of 12.5, 15, and 17.5 cm. The turbulent flow conditions were investigated by plotting velocity profiles at different sections. The bed configurations under clear water conditions were presented. The results of pier without splitter were used as reference. The study outcome that the local scour depth was decreased by the increase of splitter length and vertex angle. The near-bed flow velocity and the corresponding Froude No. downstream of the pier was minimized for 1.5D splitter length at 30° vertex angle and the minimum scour geometry was located. The effectiveness of splitters were remarkable by the decrease of flow discharge and increase of tailwater depth provided that the discontinuity of scour hole length in case of multi-circular piers. Regression analysis was employed to develop empirical formula for the estimation of maximum scour depth around circular pier with splitter.

Estimation of maximum scour depth around bridge piers under ice-covered conditions using data-driven methods

The scouring around bridge foundations is a significant concern in civil engineering. Several research has been conducted experimentally and numerically to study the maximum scour depth around the foundations of a bridge in open channel conditions. In cold regions, where ice forms on lakes, reservoirs, and rivers, the interaction between ice and hydraulic structures is further complicated. The flow distribution varies significantly leading to deeper and larger scouring around bridge foundations. The present study took advantage of the data-driven methods to investigate the impacts of ice conditions to maximum scour depth. In total, 96 datasets were extracted from previous studies. The M5 decision tree, Genetic Expression Programming (GEP), and Particle Swarm Optimization (PSO) were used in data analysis. The models were developed using the train-and-test approach to avoid over-training. The mentioned developed models were further compared with a previous empirical equation associated with the prediction of maximum scour depth around piers under ice conditions. Finally, a sensitivity analysis method was applied to evaluate the performance of the data-driven models. It was found that the approaching velocity and pier diameter play the most crucial role in determination of the maximum scour depth. The result is generally in agreement with those of previous experimental studies.

Estimation of maximum scour depth downstream of an apron under submerged wall jets

AbstractAn analysis of laboratory experimental data pertaining to local scour downstream of a rigid apron developed under wall jets is presented. The existing equations for the prediction of the maximum scour depth under wall jets are applied to the available data to evaluate their performance and bring forth their limitations. A comparison of measured scour depth with that computed by the existing equations shows that most of the existing empirical equations perform poorly. Artificial neural network (ANN)- and adaptive neuro-fuzzy interference system (ANFIS)-based models are developed using the available data, which provide simple and accurate tools for the estimation of the maximum scour depth. The key parameters that affect the maximum scour depth are densimetric Froude number, apron length, tailwater level, and median sediment size. Results obtained from ANN and ANFIS models are compared with those of empirical and regression equations by means of statistical parameters. The performance of ANN (RMSE = 0.052) and ANFIS (RMSE = 0.066) models is more satisfactory than that of empirical and regression equations.

STUDY ON ESTIMATION OF SCOURING BEHIND THE BREAKWATER

For realization of tenacious structure, it is significant to investigate the influence of scouring behind the seawall due to tsunami overflow. Although studies have been made on the estimation of maximum scour depth, there is few studies on the relationship between overflow time and scour depth.

Estimating scour below inverted siphon structures using stochastic and soft computing approaches

This paper uses nonlinear regression, Artificial Neural Network (ANN) and Genetic Programming (GP) approaches for predicting an important tangible issue i.e. scours dimensions downstream of inverted siphon structures. Dimensional analysis and nonlinear regression-based equations was proposed for estimation of maximum scour depth, location of the scour hole, location and height of the dune downstream of the structures. In addition, The GP-based formulation results are compared with experimental results and other accurate equations. The results analysis showed that the equations derived from Forward Stepwise nonlinear regression method have correlation coefficient of R2=0.962 , 0.971 and 0.991 respectively. This correlates the relative parameter of maximum scour depth (s/z) in comparison with the genetic programming (GP) model and artificial neural network (ANN) model. Furthermore, the slope of the fitted line extracted from computations and observations for dimensionless parameters generally presents a new achievement for sediment engineering and scientific community, indicating the superiority of artificial neural network (ANN) model

Estimation of maximum scour depth near a spur dike

Scour is a natural phenomenon in rivers caused by the erosive action of the flowing water on the bed and banks. Spur dikes are constructed across the flow to protect the bank from erosion by shifting of the river away from the bank. The spur dike undermines due to river-bed erosion and scouring, which is generally recognized as the main cause of spur dike failure. In this study, accuracy of existing equations for the computation of maximum scour depth has been checked with available data in the literature and data collected in the present study using graphical and statistical performance indices. Three new relationships are also proposed to estimate the maximum scour depth and maximum scour length upstream and downstream of spur dike. This new relationship for maximum scour depth is shown to perform better than other existing equations.

Suitable Bridge Pier Section for a Bridge over a Natural River

Estimation of maximum scour depth at the bridge pier is necessary for the safety and economy of the bridge design. Therefore, the phenomenon of scour around bridge piers was extensively studied from the literature to find the effect of pier shapes and inclined flow on scour depth at bridge piers. It was found from the analysis that scour depth increases with the increase of the flow angle relative to the pier axis, but for a cylindrical pier, maximum scour depth does not change with flow angle. When the flow angle is at 300, the scour depth for the cylindrical pier is smaller than other pier shapes; hence circular pier shape is more suitable for natural rivers which have possibility of changing flow direction.

Scour on Alluvial Bed Downstream of Grade-Control Structures

This paper describes an approach for predicting local scour downstream of grade control structures. The developed analysis applies the incomplete self-similarity (ISS) theory for deducing some physically based dimensionless groups controlling the geometrical pattern of the scour profile. The scour measurements available in the literature in conjunction with numerous unpublished data allow a multiregressive calibration of the ISS relationships. The experimental sample includes different bed grain-size distributions and scales of the erosive phenomenon. The results prove that the ratio between the upstream water head and the weir height is able to explain the measurements of scour depth carried out in both small- and large-scale installations. This estimation of maximum scour depth was improved, introducing variables representative of both the jet contraction and the bed particle grain-size distribution. Variables related to the longitudinal sizes of the scour profile tend to be predicted with more accuracy than those related to the scour depth and appear more influenced by the coarsest component of the alluvial bed.

TIME-VARIATION OF SCOUR IN THE VICINITY OF CIRCULAR PIERS.

A theoretical model is presented to estimate the time-variation of scour depth in an evolving scour hole at circular piers under clear-water and live-bed scour conditions with uniform and non-uniform sediments. The procedure developed for computing the time-variation of scour depth was based on the concept of the conservation of the mass of sediment, considering the horseshoe vortex system to be the main agent of scouring and assuming a layer-by-layer scouring process. The present model corresponds closely with the experimental data of time-variation of scour depth under clear-water and live-bed scour conditions with uniform and non-uniform sediments reported by various investigators. Computation is extended up to the equilibrium scour condition and the corresponding design formula for estimation of maximum scour depth is also proposed for given flow, sediment and pier conditions. The computed values of maximum scour depth showed adequate and safe estimation for bridge pier foundations.