Experimental Study Location and Percentage of Permeability of Permeable Spur Dike on the Changes of Bed Topography around Impermeable Spur Dike in Binary Combination of Permeable and Impermeable Spur Dike

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Experimental Study Location and Percentage of Permeability of Permeable Spur Dike on the Changes of Bed Topography around Impermeable Spur Dike in Binary Combination of Permeable and Impermeable Spur Dike

ارائه دهنده: Provider: Negin Farzi

اساتید راهنما: Supervisors: Majid Fazli (Ph. D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees:

زمان و تاریخ ارائه: Time and date of presentation: 2021

مکان ارائه: Place of presentation:

چکیده: Abstract: Spur dikes are structures that are mainly used to protect the river bank. The issue of scour around the spur dikes is one of the important parameters in their design. The presence of a spur dike in the flow path of the flood changes the flow pattern and directs the flow to the river axis. This change in pattern and narrowing of the river axis increases the velocity at the spur dike site and leads to scouring and movement of bed sediments and endangers the stability of the structure. Proper design of the breakwater can significantly reduce the maximum scouring depth around the spur dike. A review of previous research indicates the lack of study on the effect of the distance of protective spur dike from impermeable spur dike on the improvement of erosion and sedimentation conditions. Therefore, in this study, in order to reduce the amount of scour around the impermeable spur dike, the effect of the protective spur dike structure with different percentages of permeability and different placement distances to the impermeable spur dike was investigated in a laboratory. The experiments were performed under clear water conditions with spur dikes with zero, 30, 50 and 70% permeability percentages inside a flume with a width of 60 cm and a length of 15 m and a constant flow depth of 14 cm was performed. In this study, impermeable and permeable spur dikes were used. The impermeable spur dike was installed at a good distance in the flume. The permeable spur dike was then placed in front of the impermeable spur dike at various distances. Finally, flow was established in the flume, and the topography of the bed around the spur dike was measured using a point gauge. The results of experiments performed at different distances and different permeabilities of dual spur dikes showed that the maximum reduction of scour depth around dual spur dikes in spur dike with a permeability of 30% at a distance of 24 cm, in a spur dike with a permeability of 50% at a distance of 21 cm and in a permeability of 70% at a distance of 9 cm, respectively 76, 50 and 20.8%, have been reduced compared to the single impermeable spur dike. By increasing the distance between the spur dikes to a certain extent, there will be changes in the erosion pattern around the spur dikes, and after that, the shape of the erosion pattern will not change in terms of depth at different points or width in the longitudinal and transverse directions. By increasing the distance of the permeable spur dike from the impermeable spur dike, the scour around the impermeable spur dike decreases and around the permeable spur dike increases, resulting in an extension of the scour hole length. As the percentage of spur dike permeability increases, the width of the scouring hole does not change much, but the length of the scouring hole decreases with increasing percentage of permeability of the spur dike. Key Words: impermeable spur dike, permeable spur dike, percentage of permeability, flow pattern.

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