Observations of River Topography and Flow Around Bridges

This investigation was motivated by the amount of river, estuarine, and coastal infrastructure that is susceptible to extreme wave and flooding events. The high velocities and resulting shear stresses associated with high flow velocities are capable of scouring or depositing large quantities of sediment around hydraulic structures. Preventing the failure of these structures and sedimentation in inlets alone costs federal and state agencies billions of dollars annually. In addition to being costly, the manual monitoring of bridge scour - as mandated by the Federal Highway Administration - can be inefficient in states such as Ohio where the flood events that initiate the scour process occur sporadically. According to the National Scour Evaluation Database, there are 23326 bridges over waterways in the state of Ohio, of which 5273 are considered scour susceptible and 191 are considered \u27scour critical\u27. Previous methods for identifying bridge scour have relied on the manual (diver-based) sampling of local water depths that are generally limited to periods of low water flow. As the dynamic scour and deposition of sediments around structures is highest during periods of high flow, traditional sampling methods have limited our ability to predict quantitatively scour or deposition levels and to evaluate sediment transport models. This research is aimed at developing and testing new methods to observe riverbed topographic evolution around piles and under bridges where the structures themselves interfere with GPS based positioning. Simultaneous measurements of the velocity profiles can be used in conjunction with the observed bathymetry to make inferences about bridge scour and the effect of bridge piles on local riverbed topography. Related to problems generated by sediment scour are issues of sediment deposition in navigational channels. On the Maumee River, OH, alone, the Army Corp of Engineers spends millions of dollars annually to dredge an average of 850,000 cubic yards of sediment. With the elimination of open lake disposal of dredged sediments, an inter-agency collaboration of government and private citizens has been formed to identify possible methods for reducing the amount of deposition by reducing the soil erosion along river bank’s. Clearly, development of new observational capabilities and a subsequent increase in observations of riverbed topography and flow around structures will improve our ability to utilize available resources in the most efficient manner

Analisis Susunan Tirai Optimal Sebagai Proteksi Pada Pilar Jembatan Dari Gerusan Lokal

Local scour frequently occurs in the downstream of energy muffler or around the bridge pillars. The bridge pillar function decreases due to the scour of soil material around it. After the scour, the river base degrades resulting in position changes of pile cap, which initially under river base elevation, rises to above the river base elevation. This research conducted using experimental method in Hydraulic Laboratory of UNS's Engineering Faculty. A cylinder and round tip rectangular pillars used as the samples on the sediment Transport Demonstration Channel tool, to find out the characteristic of local scour occurred around the pillar. The analysis shows that the use of curtain to reduce local scour around the pillar is very effective. The reduction value indicated by the test is in a range of 23.12% - 38.53%.. The local scour depth of cylinder pillar after equilibrium condition achieved is in an array of 2.0 – 2.9(y/b) with an average of 2.45(y/b), while the value achieved by round tip rectangular pillar after equilibrium condition is 2.3 – 2.9(y/b) with an average of 2.6(y/b

Bridge pier flow interaction and its effect on the process of scouring

University of Technology Sydney. Faculty of Engineering and Information Technology.Previous investigations indicate that scour around bridge piers is a contributor in the failure of waterway bridges. Hence, it is essential to determine the accurate scour depth around the bridge piers. For this purpose, deep understanding of flow structures around bridge piers is very important. A number of studies on flow structures and local scour around bridge piers have been conducted in the past. Most of the studies, carried out to develop a design criterion, were based on a single column. However, in practice, bridge piers can comprise multiple columns that together support the bridge superstructure. Typically, the columns are aligned in the flow direction. The design criteria developed for a single column ignore the most important group effects for multiple columns cases such as sheltering, reinforcement and interference effects. These group effects can significantly be influenced by the variation of spacing between two columns. This is evident by the fact that insufficient investigations and development have been reported for the flow structure and maximum scour depth around bridge piers comprising multiple columns. It is therefore necessary to investigate the effects of multiple columns and spacing between them on the flow structure and local scour around bridge piers and develop a practical method to predict the maximum scour depth. The main objectives of this research work are to analyse the effect of spacing between two in-line circular columns on the flow structure and to develop a reliable method for prediction of the maximum local scour depth around bridge piers. To meet the objectives this research, detailed experimental studies on three dimensional flow structures and local scour around two-column bridge piers were carried out. A series of laboratory experiments were conducted for no column, a single column and two in-line columns cases with different spacing. Two in-line columns were installed at the centre of the flume along the longitudinal axis. Three dimensional flow velocities in three different horizontal planes were measured at different grid points within the flow using a micro acoustic doppler velocimeter (ADV). The velocity was captured at a frequency of 50Hz. Additionally, in vertical planes, particle image velocimetry (PIV) technique was employed to measure the two dimensional instantaneous velocity components. All experiments on flow structures were conducted under no scouring and clear water flow conditions. Similarly, an array of experimental tests were conducted under different flow conditions for studying the temporal development of scour depth and the maximum local scour depth around a single column and two-column bridge piers. The measured instantaneous three dimensional velocity components were analysed and the results for flow field and turbulence characteristics were presented in graphical forms using vector plots, streamline plots, contour plots and profile plots. The results indicated that the flow structures around two- columns bridge piers is more complex than that of a single column case. Furthermore, the spacing between two columns significantly affects the flow structures, particularly in the wake of the columns. It was observed that for the spacing-column diameter ratio (L/D) < 3, the vortex shedding occurred only behind the downstream column. Hence, the flow pattern was more or less similar to that of the single column case. However, the turbulence characteristics such as turbulence intensity, turbulent kinetic energy and Reynolds shear stresses were notably different from those of a single column case. When the spacing was in the range of 2 ≤ L/D ≤ 3, stronger turbulence structures were noticed behind the upstream column. Further increase in the spacing between two columns resulted in a decrease in the strength of turbulence characteristics. The experimental results on temporal development of local scour depth reveal that approximately 90% of the maximum scour depth around the upstream column was achieved within the first 10 hours of the experiments. However, for the downstream column, 90% of the scour depth was achieved within 20 hours. Similarly, the results from the experiments on local scour indicated that the maximum scour depth occurred at the upstream column, when the spacing between two columns was 2.5D. The maximum value of local scour depth for the two-column case was observed about 18% higher than the value obtained for the single column case. The reasons for maximum scour depth at the spacing of 2.5D were identified as the reinforcing effect of downstream column, the strong horseshoe vortex at upstream column, strong turbulence characteristics at the wake of upstream column, and the highest probability of occurrence of sweep events at upstream side of upstream column. Furthermore, a semi empirical equation was developed to predict the maximum scour depth as a function of the spacing between two columns. The findings of this study can be used to facilitate the position of columns when scouring is a design concern

Numerical modelling of erosion and sedimentation around offshore pipelines

In this paper a numerical model is presented for the description of the erosion and sedimentation near pipelines on the sea bottom. The model is based on the Navier-Stokes equations and the equation of motion and continuity of sediment.\ud \ud The results of the simulations have been compared with the results of tests in a large-scale facility. The agreement between the results of the simulations and the experimental results is good.\ud \ud The applicability of the method is twofold: firstly, the processes of erosion and sedimentation around bodies on the sea bottom can be simulated; secondly, the method can be used for the design of pipelines, including erosion stimulating elements, such as spoilers

A local scour prediction method for pile caps in complex piers

The outcomes of an experimental study on local scour at a pile cap are presented. Experiments were conducted with the approaching flow having an undisturbed flow depth and a threshold flow velocity. The main variables investigated were pile cap dimensions and location relative to the streambed. According to the rate of change in scour depth, the scour at a pile cap for different cap levels was divided into four cases. Equations for a correction factor for these four cases are derived. The correction factor Kc has the effect of reducing the scour depth from a corresponding full-depth pier of the same width as the pile cap. A new methodology is presented to estimate local scour depth at a pile cap as a component of a complex pier. The proposed method was evaluated with the results from this experimental study and historical measurements. The proposed method, which corresponds closely to the observations, can be used to predict local scour at a pile cap as a component of a complex pier in the superposition method. It is also applicable to the prediction of local scour due to a caisson being sunk onto a mobile bed in a current

Pola Gerusan Lokal pada Model Pilar Jembatan Lingkaran Ganda (Double Circular)

Pillar of the bridge on the stream causes changes flow patterns and local scour. Local scour will decrease the power of pillar to sustaining bridge load. Laboratory model was conducted to determine the model of local scour phenomena double circular pillar with or without protector curtain type. Basic canal model is using kampar sand with grain size d35 = 0,285 mm, d50 = 0,330 mm and d65 = 0,380 mm and spesific weight is 2,64.Froude number that used is Fr1=0,464, Fr2=0,670 and Fr3=0,769. Reynold number Fr1 scored 1658,42 is classified as transitional flow, Fr2 scored 3081,68 and Fr3 scored 4381,19 is classified as turbulent flow. Shield shows the use of gradation in moving zone. Hydrodynamic flow in pillar causes down flow that showed by scour in upstream pillar. Scour rech the equilibrium stage at minute 75. The ratio of scour depth ds/b is range from 0,03 – 0,46. The use of swivel can reduce the scours depth until 44,44%. Sediment transport analysis prove that the higher Froude is used the bigger the granules are transported. Key word : scour, model laboratory, double circular, froude, reynold, Shields, hydrodynamic flow, sediment transport

Densely distributed and real-time scour hole monitoring using piezoelectric rod sensors

This study aims to validate a piezoelectric driven-rod scour monitoring system that can sense changes in scour depth along the entire rod at its instrumented location. The proposed sensor is a polymeric slender rod with a thin strip of polyvinylidene fluoride that runs through its midline. Extraction of the fundamental frequency allows the direct calculation of the exposed length (or scour depth) of the slender rod undergoing fluid flow excitation. First, laboratory validation in dry conditions is presented. Second, hydrodynamic testing of the sensor system in a soil-bed flume is discussed. Each rod was installed using a three-dimensional-printed footing designed for ease of installation and stabilization during testing. The sensors were installed in a layout designed to capture symmetric scour conditions around a scaled pier. In order to analyze the system out of steady-state conditions, water velocity was increased in stages during testing to induce different degrees of scour. As ambient water flow excited the portion of the exposed rods, the embedded piezoelectric element outputted a time-varying voltage signal. Different methods were then employed to extract the fundamental frequency of each rod, and the results were compared. Further testing was also performed to characterize the relationship between frequency outputs and flow velocity, which were previously thought to be independent. In general, the proposed driven-rod scour monitoring system successfully captured changing frequencies under varied flow conditions

Validation of some bridge pier scour formulae using field and laboratory data

Estimation of maximum local scour depth at the bride pier site is necessary for the safety and economy of the designed bridge. Numerous formulae are available and almost all of these formulae were developed based on laboratory data. Validation of these formulae is necessary in order to ascertain which of the formulae will give a reasonable estimate of the local scour depth. In this study, four commonly cited formulae were selected for the validation process using both the laboratory and field data. They were the Colorado State University (CSU), Melville and Sutherland, Jain and Fisher, and Laursen and Toch formula. The experimental data was obtained from the laboratory model study done at University Putra Malaysia, whilst the field data were obtained from 14 bridges sites. Three statistical tests were carried out to determine the formula that gives minimum prediction errors. Comparison between the predicted and measured depth of scour from the experimental and field data showed that the Laursen and Toch and the CSU formulae appeared to give a reasonable estimate. Whilst the Melville and Sutherland and Jain and Fisher formulae appeared to over-predict the depth of the scour. This observation was supported by the statistical tests