جستجوی مقالات مرتبط با کلیدواژه "گروه پایه کج" در نشریات گروه "آب و خاک"

When the bridge piers are located in front of the water flow, vortices are formed against it and due to their activity, the materials of the river bed are eroded around the bridge piers and the scouring hole is created. If the foundation depth and bridge pier piles are insufficient, the bridge will fail.The study of total shear stress in the flow bed at different leveling of the pile caps shows that the highest shear stress is created when the pile cap position is at the same level as the river bed; by installing the pile cap at a lower level than the river bed, the maximum shear stress decreases. This may be due to the fact that in this case, the distance between the pier group increases and the presence of the second pier decreases the flow rate in the pier group and different pier in the one pier group acts as the two independent piers in the formation of the flow pattern. By comparing the final longitudinal sections of the scouring at different leveling of the pile cap, it is concluded that the largest reduction in scouring depth occurs in aerofoil-shaped pile caps and pile caps with the sharper nose and better aerodynamic shapes are good options to control the horseshoe vortices and will reduce the scouring depth around the inclined pier group.

Hydraulic structures situated as an obstacle in front of water flow that changed the flow pattern in their vicinity and causing the local scour around the structure. The scour around the bridge pier is one of the most important phenomena in sediment hydraulics, which creates a hole around the pier and undermines its stability. Different methods have been proposed to prevent or reduce the local scour. In this study, the effects of collars, nanoclay materials and angle of piers have been studied in pier group. The results show that for the pier with the angle of 15 degree was observed the greatest decrease in the depth of the scour hole. Studies show that in the group pier with inclination angle of 15 degrees, there was 14 percent scour hole reduction and with presence of a collar the reduction of scour hole was 86 percent. Also, by using nanoclay materials, the depth of the scour hole in the without collar condition was reduced by 18.5%.

Bridges are one of the main components of the transportation. One of the main causes of bridges failure, especially during flood times, is the development of scour depth near and below the pier and its foundation. Therefore, protecting the pier from scouring is an important issue in the safety of bridges at design stage . In general, scouring can be divided into three types: general scour, scouring due to the contraction of the river section and local scouring such as around bridges and abutments . The flow pattern around the bridge pier include downflow, horseshoe vortices, and wake vortices. By increasing the local shear stress in the vicinity of the bridge piers, these vortices cause erosion in front of the piers and gradually extend to the sides of those. The separation of the flow at the sides of the pier creates so-called wake vortices, which is unstable and shed alternatively from each side of the pier. These vortices act as little tornadoes lifting the sediment particles from the bed. As a result of these processes, a scour hole is formed around the pier and gradually developed. Regarding to the importance of scour around the bridge piers, many studies have been conducted on understanding of governing process and estimation of the scour depth around bridge pier. Although many literature have been documented for single pier but due to geotechnical and economical reasons, multiple-pile bridge piers and complex piers have become popular in bridge design and have attracted interest of researchers. Due to the importance of reduction of scour around the bridges, different countermeasures have been introduced and evaluated in the literature. In general, the countermeasures against pier scour are broadly classified into two categories: (1) flow-altering countermeasures, and (2) bed-armoring countermeasures.One of the devices to reduce scour depth around the bridges piers is an installation of bed sill in vicinity of the foundation. In this research, the effect of the upstream sill on time development and maximum scour depth around inclined bridge pier group was investigated for different pile cap thicknesses, top level installation of pile caps, array and diameter of piles. The bridge pier consist of two rectangular piers with 2.5 and 3.5 cm dimensions which mounted at an angle of 28 degrees on a pile cap with 10 cm width, 16 cm length, 3 and 5cm thickness which placed on an array of 2×2 and 2×3 piles with different diameters. The experiments were performed for relative flow depth (y/D) 6.42, relative pile cap levels (Z/D) 0, 1, 2, 3, 4, relative pile diameter levels (dp/D) 0.57 and 0.85 in clear water conditions. A total of 72 runs was performed for hydraulic and geometric conditions. Comparison of the results indicated that at the level of Z/D =0, by installation of sill at upstream of pile cap, the maximum scour depth decreases 24.5 percent. At the top installation of pile cap of Z/D =1, the maximum scour depth decreases 29 percent of sill installation location at upstream of pile cap. At the level of Z/D =2, by installation of sill at upstream of pile cap, the maximum scour depth decreases 32.5 percent. At the top installation of pile cap of Z/D =3, the maximum scour depth decreases 35 percent of sill installation location at upstream of pile cap. At the level of Z/D=4, by installation of sill at upstream of pile cap, the maximum scour depth decreases 36.8 percent. Comparison of results indicated that installation of upstream sill length of scour hole decreased 26 percent approximately. However, width of scour hole increased 2-3 times of corresponding scour width of non-sill conditions.

In this research, the effects of pile cap thickness and its top level of installation, arrangement and diameter of piles on variation of local scour around the inclined bridge piers group were investigated experimentally. A Physical model of piers group having two inclined rectangular piers with 28 degrees inclination angle was constructed on a pile cap. Experiments were performed on piles group with relative diameters ( ) of 0.6 and 0.9, piles arrangement of 2×2 and 2×3, relative pile cap thicknesses ( ) of 0.9 and 1.4 and the pile cap relative installation levels ( ) of 1.5, 1, 0.5, 0 and also its buried condition at the level of -0.7 and -1.2. Comparison of the maximum scour depth indicated that the change of pile arrangement from 2×2 to 2×3 caused 50 and 60 percent increases in the scour depth related to the ratio of with the amount of 0.6 ad 0.9, respectively. However, changes of the pile diameter and arrangement did not have any effect on the maximum scour depth as pile cap installed in the same level of bed or lower than it i.e. in buried condition. Comparison of the results showed that changes of the pile cap thickness from 0.9 to 1.4 times the pier width, caused the maximum scour depth for all pile geometry and top level installation of the pile cap to be increased 20 percent approximately. Furthermore, as pile diameter increased from 0.6 to 0.9 bridge pier width, the maximum scour depth for installation of the pile cap above the bed increased 5 and 10 percent approximately for pile arrangement of 2×2 and 2×3, respectively.

Bridges are certainly one of the most important structures but costly service elements in a transport system. The bridges are very required to access the damaged areas in emergency situations such as floods and earthquakes. Scour around the foundations of bridge piers exposed to the flowing water than can destroy the bridge itself is a subject of major concern. Flow pattern is known as responsible for all changes in stream bed. Any obstacle in the channel can form new flow patterns causing additional shear stress exerted on the bed than the equilibrium condition of the absence of the obstacle. Appropriate shaping of flow pattern and proper selecting of pier geometry and the location of bridge piers can be one of the proper methods in reduction of scour amount which is the main subject of the present study.
Inclined bridge group pier is a type of bridges with modern geometry based on development in building technology of structures. Many of these bridges have been built all around the world and the 8th bridge built crossing the Karun River in Ahvaz is a sample of the Iranian ones considered in this research. Hydrodynamic behavior of flow is investigated around the inclined bridge group pier settled on foundation using the FLOW-3D numerical model. Inclined bridge group pier investigated in this study, includes two rectangular piers which are 2.5 cm long and 3.5 cm wide and set in an angle of 28 degree on rectangular foundation which is 16 cm long and 10 cm wide and installed in three different foundation levels namely at, above and below the bed levels. The physical model of prototype pier considered in this study was constructed to the scale of 1:190 of the Ahvaz 8th bridge. In order to verify the accuracy of the numerical model, velocity data obtained from image processing technique were used.
Due to non- linearity and interactions between various phenomena involved, flow pattern around the piers group is entirely different than that for a single pier and consequently the outcomes of the flow pattern around single pier cannot be generalized to the pier group. At all levels of foundation setting, longitudinal component of flow velocity increases surrounding the first pier. The increase in the area and its extension towards downstream is caused by the constriction the flow due to the pier and area rotating of the wake vortex in downstream. When the pier foundation is set at the stream bed, the bed rotating flows extend to a distance between the two piers from near the bed up to the middle of flow depth while in upstream of the second pier and near water surface, the stream lines become parallel to the bed. The comparison of the results of the changes in bed shear stress in the situations of foundation setting in different levels showed that the maximum shear stress occurred when the foundation level is at the bed level and the maximum shear stress exerted on the bed decreases by factors of 17% and 53% in the cases of foundation level to be below and above bed levels, respectively. In addition, the results showed that, the amount of vortex flows increased in upstream piers group and near bed in the case of setting the foundation above the bed. This is because of the fact that the volume of piers group acted as obstacle against flow was more than other level settings. Furthermore, based on the obtained results, in the case of foundation level is set at the bed, the quantity and development zone of vortex flow are much higher than those observed when the setting foundation is below the bed level. This can be attributed to the higher effect of the second pier on the flow pattern being between the first and the second piers. Stream lines turn downward in the range between piers group, and after the collision to bed turn upward to water surface and cause to form rotating flow and hence high turbulence intensity in the area. In the near water surface and the center of group piers, stream lines were observed to be parallel to the bed and caused low turbulence intensity in this area.
The results showed that the levels of setting foundation have a significant effect on hydrodynamic characteristics and flow pattern around the piers. By increasing the dimensionless height of the setting foundation from -1 to 0.5 vortices formed in the downstream piers group is strengthen more and the results from the numerical model are consistent with the results of experimental scour around piers group in all three levels of setting foundations. When the foundation setting is at the bed level, the maximum bed shear stress is observed. The maximum bed shear stress is decreased by factors of 17 and 53 percent when the foundation to be set below and above bed levels, respectively.

The main cause of collapse of bridges is scour around bridge piers. Therefore, knowledge about the effective parameters and estimation of maximum scour depth has an important rule on the safe design of bridges in rivers. The aim of this research is evaluation of optimized ANFIS parameters with GA on prediction of maximum scour depth and comparison with all FIS generator of Matlab Toolbox ANFIS. 48 set of experimental data of scour around incline bridge piers were used. To comparison of performance of results, R2 and RMSE were utilized. Analysis of results showed that GENFIS1 generator of ANFIS toolbox in Matlab had the best performance, which could predict maximum scour with R2 and RMSE, 0.976 and 0.053, respectively. Comparison of predicted scour depths indicated that optimization of ANFIS parameters had better prediction of desired parameters with R2 and RMSE, 0.992 and 0.02537 in comparison of ANFIS toolbox in Matlab software.

After construction of bridge pier in a river, a 3D complex flow pattern forms around piers and erosion of bed material occurs and if foundation depth or piles depth was not sufficient, the bridge will be collapsed. One of devices to reduction of scour around bridge piers is an installation of sill beside of piers. In this research, effect of sill on reduction of scour around the inclined bridges piers group under various hydraulic condition and top level of installation of foundation was investigated experimentally. The model of bridge pier was 1/190 scaled of 8th bridges of Ahvaz, Iran, which had inclined rectangular of 2.5 cm length and 3.5 cm width and was placed on the foundation of 10 cm width and 16 cm of length with inclination of 28 degree. Experiments was conducted for different location of sill (front, middle and downstream) of foundation which installed at relative level, height of top of foundation to width of it, -1, -0.5, 0 and 1. Comparison of results showed that installation of sill in front of foundation had the best performance to decrease of scour depth. Furthermore, the reduction of scour depth as the top level of foundation was placed at same level of bed, was considerable.

Advancement of technology in construction of structure caused to design modern type of bridge piers including inclined bridge piers group. Due to importance of identifying effective mechanisms of scour around this type of bridge piers, in this research the effect of flow parameter and level of bridge foundation on the scour depth was investigated. Bridge piers group included two inclined rectangular piers of 2.5cm width and 3.5cm length which installed at the angle of 28 degree on the top of rectangular foundation of 10cm width and 16cm length. Experiments were performed for various relative velocities, depth of flow and relative top level of the foundation from the channel bed (Z/D*) -1 up to 1. The results showed that the velocity of flow has more effect on the local scour depth in comparison of the flow depth. Comparison of results for different levels of the foundation showed that level of the foundation has significant effect on the scour depth. A maximum and a minimum scour occurred for relative foundation level 1 and -0.5. Furthermore, except of relative foundation - 0.5, the scour at the inclined bridge level is more than individual pier.