Showing 33 results for Scour
S. Kouchakzadeh,
Volume 5, Issue 1 (4-2001)
Abstract
Bridge abutments are usually located in the floodplain zone of rivers where velocity and shear stress are not uniformly distributed. The influence of channel geometry and lateral momentum transfer in compound flow field on the scouring phenomenon has not been fully investigated and understood yet. The impact of lateral momentum transfer on the local scour at abutments terminating in the floodplain of a compound channel is presented in this paper.
It is shown that, by accounting for lateral momentum transfer at small floodplain/main channel depth ratios (λa/H<0.3), estimates of maximum local scour depth are increased by up to 30%. Therefore, ignoring the influence of the lateral momentum transfer, in such circumstances, might result in unrealistic estimation of the scour depth. To draw a more general conclusion, more data are required to assess the influence of different parameters affecting the phenomenon in compound flow conditions.
M. Heidarpour, H. Afzalimehr, M. Naderi Bani,
Volume 7, Issue 3 (10-2003)
Abstract
The use of slot through a pier is a new method proposed to control local scour at bridge piers. In this study, control of local scour at bridge pier is studied using 20 pier models under clear water conditions. The models consist of one circular pier without slot, three round-nosed piers without slot, and 16 piers with slot. Two slot lengths were chosen (yl=b and yl=2b, where y1 is the length of slot and b is the width (diameter) of the pier). Furthermore, they were located at two positions (near the bed and near the water surface).
The results showed that for a circular pier, the slots with the lengths of b and 2b, located near the water surface, had no influence on the equilibrium scour depth. It was also found that for all piers, maximum reduction in scour depth occurred for piers with a slot length yl=2b and close to the bed. Also, the efficacy of a slot for scour protection in the case of a round-nosed pier was more than a circular pier (with a diameter equal to the width of a round-nosed pier).
Malihe Keykhee, M Heydarpor, Farhad Mosavi,
Volume 13, Issue 49 (10-2009)
Abstract
Ripraps are placed around bridge piers to prevent scour and secure the piers from failure. Proper riprap cover is essential to be economical. The present study examines using of riprap for reduction of local scour in piers group and the results are compared with data from riprap on a single pier. The models consist of two and three circular-shaped piers in line with the flow, with the diameter of 0.02 m and pier spacing of twice and four times the pier diameter. Four uniform riprap sizes with the diameters of 2.86, 3.67, 4.38 and 5.18 mm were used to cover the piers. The results showed that the effect of wake vortices formed at the downstream side of piers group was decreased as compared with single pier. The reinforcing and sheltering effects caused 31% decrease in front pier and 60% increase in back pier, respectively, for the length of cover riprap. The reinforcing and sheltering effects were decreased by increasing pier spacing, but the riprap pattern was not affected. In triple piers group, scour depth in the second pier was less than the first pier and in the third pier was less than the first and second piers. In double and triple piers group, the sheltering effect reduced the scour depth (46% and 54%, respectively) in the back pier with respect to the single pier. Reduction of dimensions in scour hole of back pier in triple piers group was 67% with respect to double piers group, which is the result of sheltering effect of first and second piers. The best shape for the riprap was semi-oval. The riprap length in double and triple piers group was reduced by 31% and 37.5%, respectively, as compared with the single pier.
A. Masjedi, M. Gholamzadeh Mahmoodi,
Volume 15, Issue 55 (4-2011)
Abstract
Every year river flooding causes serious damage to the bridges at the time needed most. One of the most effective factors causing bridge failure is scouring around the piers in a river bend. One of the methods to decrease scouring around the bridge piers is fitting them with a coller on the piers. The collars protect the river bed against vortex flow in the vicinity of the pier base. An experiment was conducted to study lab flumes made of Plaxiglass with a 180 degree bend and 2.8 m central radius and a 0.6 m width. In this study, a 6cm diameter pier was placed with a circular collar with four different collar sizes in one position in bend with constant discharge and depth under clear-water conditions. The collar was placed at four different elevations. The soil material had a diameter of d50 = 2mm and geometric standard deviation of σg = 1.3. The results of the model study indicated that the maximum depth scouring was highly dependent on the experimental duration. It was observed that as the size of a collar plate increases, the scour decreases. So, minimum depth of scour is dependent on the 3D coller and -0.1D elevation. Circular collar results in maximum reduction in scour depth (93%) compared with no circular collar.
A. R. Masjedi, H. Kazemi, A. Moradi ,
Volume 15, Issue 57 (10-2011)
Abstract
In this research, the effect of installing position of bridge pier on scouring depth was studied in a bend laboratory flume, which is made of Plexiglas with 180 bend and a relative radius of Rc/B=4.7. Tests were conducted using one pier 6 cm in diameter under four discharge conditions with constant depth of 12 cm and clear-water conditions. Flume bed was fully paved by uniform sand. It was found that maximum scouring depth occurred in bend when bridge pier was installed in the position of 60 degrees. Also, in all situations increased scouring depth occurred by increasing discharge.
P. Shojaei, D. Farsadizadeh , A. Hoseinzadeh Dalir,
Volume 15, Issue 57 (10-2011)
Abstract
Submerged vanes are low aspect ratio flow-training structures mounted vertically on the river bed at an angle to the prevailing flow. The aim of application of vane is to generate a secondary circulation in the main flow, designed to modify the near-bed flow pattern and thus redistribute flow and sediment transport within the channel cross section. Collar is a flat sheet with low thickness fixed vertically on the pier at stream bed level or near it. Installation of a collar leads to protect the river bed against the direct impact of downflow produced at the upstream face of the pier and therefore reduces the scour depth. This research is a laboratory study that examines the effectiveness of submerged vanes and combination of submerged vanes and collar as a pier scour protection device. Experiments were conducted in an 8 m long and 0.8 m wide flume and a cylindrical pier used was 6 cm in diameter. Clear-water scour tests with u*/u*c = 0.9 were performed with a collar 3 times wider than the pier diameter at the stream bed level and submerged vanes 1.5 times longer than the pier diameter at the stream bed level (H=0). Different arrays of vanes with different angles to main flow direction were employed. The highest reduction in the depth of scour hole with four vanes and a collar showed 61% reduction in scour depth.
E. Nohani, M. Shafai Bejestan, A. R. Masjedi,
Volume 18, Issue 68 (9-2014)
Abstract
Local scour around piers is the major cause of their foundation failure in the river bends that endangers the stability of the structure and its efficiency. Riprap is commonly placed around the bridges piers for local scour protection. The aim of this study was to present an equation for estimating stable riprap diameter around a cylindrical bridge pier in river bends. In this study, using an experimental model with a 180 degree bend stability, four different riprap diameters under different flow conditions and clear water flow were studied. Empirical relationships based on dimensional analysis for stable riprap design around the bridge foundation was presented. The experimental results were compared with equations provided by other researchers, including Lauchlan (1999), Parola (1995) and Chiew (1995). Results showed that the presented equation in this paper has a good precision. The simple equation presented in this study included all factors important to the instability of the riprap, and recommends designing ripraps around the bridge pier in river bends.
M. Zare , T. Honar1,
Volume 19, Issue 74 (1-2016)
Abstract
The most important cause of concern about the stability of bridge foundation is the occurrence of scour around bridge piers. Therefore, different methods have been proposed to prevent or reduce scouring around bridge piers. The use of groynes is one of the modern methods to control and reduce local scour. In the present study, the effect of a solid groyne on reduction of the scour depth around a cylindrical bridge pier, located in the bend of a laboratory flume is assessed. Experiments were conducted for groyne model angled at 50˚, 90˚ and 120˚ to the downstream channel sidewall with three flow rates of 47, 49 and 51 liters per second in a sediment free condition. Results showed that in at ratios of velocity to critical velocity and all groyne angles, in comparison with no groyne, the scour depth was reduced. At all ratios of velocity to critical velocity, the best operation was related to normal groyne and the average operation of repelling groyne was better than attracting groyne. The operation of normal groyne decreased and attracting groyne function improved as the flow rate increased. Also, the normal groyne (ratio of velocity to critical velocity equal to 0.87) had the best effect on reducing the scour depth (by about 71.4 percent).
Mr A. Nouri Imamzadehei, Manouchehr Heidarpour, M. R. Nouri Imamzadehei, B. Ghorbani,
Volume 21, Issue 2 (8-2017)
Abstract
Flood currents are considered threatening factors by creating local scour along bridge piers. One method for decreasing local scour is to strengthen the bed against imposed tensions. Among methods which can directly be appropriate in decreasing and controlling local scour of bridge piers is to employ geotextile around bridge piers. In the present study, the effect of geotextile layer in decreasing local scour of cylindrical single-pier was investigated with the purpose of proposing the best effective method of covering bridge pier. So, layers with circular and oval shapes were put around the pier, in proportion with pier diameter, and the performance of each was compared with the unprotected pier. Test results showed that with installing the oval geotextile layer, final scour depth around the pier reached to 1.25D. Also, comparing geotextile and collar with 2D diameter, the delay of scour process around geotextile was 40 times higher than the collar, but the collar decreased the ultimate scour depth further than geotextile.
K. Qaderi, R. Jafarinia, B. Bakhtiari, Z. Afzali Goruh,
Volume 22, Issue 1 (6-2018)
Abstract
The investigation of local scour below hydraulic structures is so complex that makes it difficult to establish a general model to provide an accurate estimation for the local scour dimension. During the last decades, Data Driven Methods (DDM) have been used extensively in the modeling and prediction of unknown or complex behaviors of systems One of these methods is Group Method of Data Handling (GMDH), that is a self-organization approach and increasingly produces a complex model during the performance evaluation of the input and output data sets. So, the objective of this study was to investigate the potential of the GMDH method in the accurate estimation of local scouring geometry (maximum scour depth, the distance of maximum local scour depth till Ski-jump bucket and length of local scour) below the Siphon spillway with Ski-jump bucket energy dissipaters for a set of experimental data. 80% of data set was used for the training period and the remaining data set was used for the test period. The average values of MSRE, MPRE, CE and RB for the nonlinear second order transfer function (FUNC1) were calculated to be 0.92, 0.02, 8.74, -0.01; also, for the nonlinear first order transfer function (FUNC2), they were 0.85, 0.02, 10.43 and -0.02, respectively. The results indicated that the performance of FUNC1 was better than FUNC2. Also, the value of the coefficient of determination (R2) for the estimation of local scour dimension using different methods such as s linear regression, nonlinear regression and ANN indicated the high performance of the developed model of GMDH in the accurate estimation for local scour dimensions.
A. Masjedi, B. Jafari,
Volume 22, Issue 3 (11-2018)
Abstract
In this study, the performance of slot in the spur dike was evaluated as a way to reduce the scouring around the installed flat spur dike in a 180 degree bend and the development of scouring in the slotted spur dike was compared with that of the spur dike with no slot. To evaluate the effect of the slot on the development of scouring around it, a flat spur dike made of Plax Glass was installed in a position of 70 degrees from a bend (180 degrees) in the flume bed. After determining the maximum of scouring depth at the tip, to reduce the scouring around the spur dike, two slots with the determined height were placed in 4 different positions in the spur dike. Experiments with 4 different discharges and constant flow depth in clear water conditions were conducted. The results of the experiments showed that the created the slot reduced the scouring depth toward the spur dike. In both slots, the minimum of scouring depth was seen in a model with the closest position of the slot toward tip, and its maximum was seen in a model with the farthest position from the slot.
Z. Talebi, H. Arvanaghi,
Volume 22, Issue 4 (3-2019)
Abstract
Flow pattern around the bridge piers includes water surface profile, velocity profile, shear velocity, shear stress distribution, etc. In this research, the effects of the base shape along with scale effects on the flow pattern around the rectangular bridge piers were numerically calculated through "Fluent Software", using Horizontal Velocity Distribution (Vx) and Vertical Velocity Distribution (Vy) criteria. The results showed that in studying the horizontal component of velocity (Vx) for the rectangular bridge piers, the vortices activity radius was 8 times of the length of the pier, and the minimum channel width for vortices activity was 16 times of the length of the Bridge pier; also, the minimum channel length in front of the pier was 4 times of the length of the pier and behind which, it was 25 times more than the bridge pier. Finally, the minimum channel length for the vortexes activity was calculated to be 29 times more than the bridge pier length. Furthermore, for the vertical component of velocity, the flow pattern around the base of the bridge cannot be an appropriate parameter for checking the effects of the length and width of the channel.
H. Davodi, A. R. Masjedi, M. Heidarneja, A. Bordbar, A. A. Kamanbedast,
Volume 23, Issue 2 (9-2019)
Abstract
In this study, some experiments were carried out in a rectangular plexiglass flume to study the effect of the cable around a vertical tripod and two piles groups with different angles. In this research, a series of experiments were performed by placing a cylindrical vertical pileand two piles groups with different angles separately in two modes including with cable and without cable. The experiments were carried out using three types of cable with various diameters, number of threads and thread angles at a constant discharge in clear water. In each experiment, scour depth at the end of the test was measured; then, the scour depth was calculated in different conditions using the obtained data. The best configuration in the vertical pier and piers group was found for the cable-pier diameter ratio of 0.1, the thread angle of 15° and the triple threads. The result indicated that the scour reduction was enhanced as the cable diameter and threads were increased and the thread angle was decreased. So in the piers group of 28 and 38°, scour depth was reduced to about 43, 49 and 56%.
M. Khalaj, S. Gohari, S. S. Okhravi,
Volume 23, Issue 3 (12-2019)
Abstract
Experimental and numerical study of scouring pattern on the direct and polo-shaped groynes have been investigated in this paper. In this study, direct and polo-shaped groynes models with a length of 0.12 meter have been used in discharges of 10.5, 15, 20 liters per second in a direct flume. The results showed that the maximum scour depth formed around the groyne head of direct and polo-shaped types has increased with augmentation of flow discharge, which was 0.095 and 0.104 meter in the case of 20 L/s discharge respectively. Also, the width of scour hole was 2.25 and 2 times of effective length of the groyne in direct and polo-shaped groynes respectively. In this regards, maximum scour depth around the head of groyne was seen 0.87 and 0.79 times of the effective length of the groyne. Sand form located at downstream of the direct groyne at the distance of 0.09 and 0.15 meters from the side wall of direct groyne was stretched and extended to about 1.3 times of the channel width as well. While the length of the sand form for direct groyne was 1.15 times of the channel width. Overall, the dimensions of the scour hole around the polo-shaped groyne, was less than the direct groyne. In addition to understanding the hydraulic behaviour around the groyne, Flow3D software was used. Statistical survey of the results obtained by experimental and numerical models attested that the relative error of the numerical model could be about 20%, which shows an appropriate performance of using Flow3D for predicting the maximum scour depth.
E. Shaker, S. M. Kashefipour, M. Shafai Bajestan,
Volume 23, Issue 4 (2-2020)
Abstract
Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph’s parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion’s ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph’s peak led to increasing depth erosion from 7% to 22%.
M. Pourmirza, A. Kamanbedast,
Volume 23, Issue 4 (12-2019)
Abstract
Occurrence of local scour is one of the most significant causes of damage to the pipes. Therefore, safe and economical design of pipes in the flow path requires a good estimate. In this study, based on the important and effective parameters in the scouring phenomenon, in order to develop educational patterns according to the data obtained in the laboratory of Ahvaz Islamic Azad University, models based on artificial neural networks were created with the NeuroSolution5 software. MLP, GFF and RBF were the models used in this study; after comparing, MLP was selected as the basis for our study. Finally, the effect of each parameter on scouring was determined using the artificial neural networks technique, based on which the shields parameter with a very high effect (more than 95 percent) was determined as one of the most effective causes of the local scour.
Gh. Safarinejadi, M. Heidarnejad, A. Bordbar, M. H. Pourmohammadi, A. Kamanbedast,
Volume 23, Issue 4 (12-2019)
Abstract
The use of free launch jets in flip bucket structures with associated submerged ponds, in the appropriate geological, and topographic and hydraulic conditions, could have significant economic and safety benefits. In this research, the downstream scour phenomenon of a flip bucket jet was investigated in free conditions, as well as in the presence of a trapezoidal and triangular slot in the coastal manner with different layout intervals at flow rate of 9, with a total of 45 experiments. The results of this study showed that the presence of the slot had significant effects on the depth and range of scour, so that the fit bucket jet with alternate triangular slots reduced the scour by about 12.7%, as compared to the no slot mode. Moreover, the maximum scour depth occurred in the bucket mode with the alternate trapezoidal slots in the more favorable interval than the rest of the models. Then, the results were compared with several empirical formulas and Veronese A relation showed closer results to the actual values.
H. Ghafari, M. A. Zomorodian,
Volume 23, Issue 4 (12-2019)
Abstract
One of the main reasons for bridge failure is the local scour around the pier. Pier groups are popular in the structural designs due to economical and geotechnical reasons. The mechanism of scouring at the pier groups is more complicated than the single one. In this study, the scour around group piers in the sandy soil and a mixture of sand and clay in some relative compaction equal to 90% and the optimum moisture was studied. The arrangement of the group piers was 1pier * 3pier and 3pier * 1pier along and transverse of the flow direction, respectively, at the interval space of D, 2D and 2.5D intervals. The effect of the Bentonite clay content was investigated. Finally, by using Kaolinite clay, the effect of the clay mineral was studied. The results showed that the scouring depth was different not only in cohesive and non- cohesive soils, but also according to the type of the clay mineral. The use of 10% bentonite clay mixed with sand reduced scour more than 90%, as compared to the sandy soil. On the other hand, using 15% of kaolin in the similar conditions reduced scour depth by only a 34%, in comparison to the sandy soil.
M. Majedi Asl, S. Valizadeh,
Volume 23, Issue 4 (12-2019)
Abstract
Local scour around the foundation of marine and hydraulic structures is one of the most important factors in the instability and destruction of these structures. False prediction of scour depth around bridges has caused financial losses in plasticization and endangered many people's lives. Therefore, an accurate estimation of this complex phenomenon around the bridges is necessary. Also, since the formulas presented by different researchers relate to laboratory conditions, they are less true and less accurate in other situations. Recently, many researchers have tried to introduce new methods and models called soft calculations in predicting this phenomenon. In this research, 146 different laboratory data series (three different laboratory conditions) were analyzed using a backup vector machine to predict scour depth around the bridge head. These data are presented in the form of various combinations of input parameters which, respectively, represent thickness under the slippery layer, Reynolds number, critical velocity, Shields parameter, velocity Shear, average speed, flow depth, the average diameter of the particles and diameter of the bridge. The parameters in two different scenarios (the mode with dimension and mode) were introduced into the SVM network and the results of this machine were compared with those obtained from the experimental formulas and relations presented in this study. The results showed that in the first scenario, the combination of No. 5 with input parameters () and in the second scenario, the combination No. 5 with input parameters () for the test stage were selected as the best model. It was also concluded from the results that the scenario two (the state with dimension) in predicting the scour depth around the vertical single-pillar provided a more accurate estimate than the first scenario (barrier state). At the end, the sensitivity analysis was carried out on the parameters and the parameters D, U*, V were selected, respectively, as the most effective parameters
M. Majedi Asl, R. Daneshfaraz, S. Valizadeh,
Volume 24, Issue 2 (7-2020)
Abstract
Sand mining from rivers is one of the biggest concerns in the science today. Certain principles and rules for choosing the right place for mining materials and the amount of this mining are missing in the design codes. Therefore, mining of river materials from sites with less potential and near structures has been occasionally seen. In the present study, it has been attempted to reinforce the structure to control the impact of the mining of material, which results in the increased scour by changing the flow pattern around the structure. The experiments were carried out in two simple and armed modes, in sand bed with a grain size of 0.78 mm, with a length of 4.25 meters, inside a canal of 13 meters in length and 1.2 meters in width. The extent of scouring along the longitudinal and transverse directions in different times from the start to the scouring equilibrium was investigated for all substrates under sub-critical flow conditions (range 0.5-0.25). The results showed that the use of a cable-protected method in the upstream pit led to 29.6% reduction in the maximum scour depth at the front and 34% reduction in the back of the pier; also, in the downstream of the pit, it reduced the maximum scour depth by 15% at the front of the pier. Therefore, the cable arrangement used at the piers surface, according to the current research method, resulted in a significant reduction in the depth and extent of scouring in the pier group of the bridge.
