كنترل آب شكستگي موضعي پايه استوانه اي پل با تسليح خاك اطراف پايه به كمك ژئوتكستايل

چكيده انگليسي :

Control of the local scouring around the cylindrical bridge pier usingarmed soil by geotextileAbstract Scour is a natural phenomenon which occurs as a result of erosion in bed and drift riversides by watercurrent This phenomenon is created locally as a result of mutual effect of water way geometry bed andcurrent specifications around the pier As a matter of fact when a currents strikes bridge piers holes aremade around the pier and complex vortex systems are created whose performance causes a hole around pierscalled a scour hole The development of this hole around the pier causes under the foundations to get emptyleading to their destruction and finally the destruction of the bridge Prediction of depth and the final statusof scour hole are the most important cases of hydraulic design of bridges In order to prevent and decreasescour at the bridge pier two basic methods have been presented One of them is the direct method in whichthe resistance of the bed against tension increases and the other is the indirect method in which the effect ofthe destructive forces is reduced by changing the current pattern around the pier Geotextiles which areproduced from polypropylene and polyester fibers form a large group of geosynthetic products and are onthe market in woven and non woven groups from the point of commercial structure this material can be usedto strengthen river beds adjacent to bridge piers and to control the scour around them concurrently playingthe role of riprap and collar On this basis the present research has been carried out with the aim todetermine the efficiency of geotextile cover in controlling the scour in bridge piers and in selecting the bestdimensions of this cover appropriate to the pier dimensions in order to minimize the scour phenomenon Due to the existence of current separation phenomenon and three dimensional current along with sedimenttransfer as well as bed changes scour analysis is theoretically very difficult hence most of the researchactivities regarding this phenomenon are based on laboratory models The tests of this research have beencarried out in laboratory flume in the hydraulics laboratory of the University of Shahrekord This flume has asquare cross section of 60cm 60cm and a length of 20 meters The dimensions of the reinforced plates used geotextiles in the tests of this research consisted of oval shaped plates in various sizes with a proportion ofthe pier diameter covering around the cylindrical pier in various radial and were used along treatmentevidence without coverage to determine the best cover Results show that By using geotextile with anappropriate cover apart from a delay in scouring process the scour location is transferred to downstream andthe scour depth is decreased In other words the geotextile layer has a dual performance in decreasing scour that is it both strengthens the bed against the current and changes the flow pattern Geotextile layer can actbetter than riprap in deceasing scour at bridge pier because in addition to the riprap properties it has noscreen destruction and the layer remains fixed due to its small openings Hence scour close to the geotextilelayer is less with the riprap cover and similar geotextile On this base with regard to negligible amount ofscour the semi oval pattern with more coverage in behind the pier is suggestsd as the best pattern ingeotextile installation Studies on stress and velocity profiles indicate horseshoe vortexes and downwardcurrent in upstream and wake vortexes in downstream the pier and led numerrous irregularities in flowcharacteristics Key words local scour bridge pier geotextile coverage pattern flow characteristics

نوري امام زاده ئي، علي

كنترل آب شكستگي موضعي پايه استوانه اي پل با تسليح خاك اطراف پايه به كمك ژئوتكستايل

الگوي پوشش , ساختار جريان در اطراف پايه