بررسی آزمایشگاهی تاثیر استفاده از سنگ‌چین و پوشش گیاهی بر آب ‌شستگی اطراف تکیه‌گاه پل

هدف از انجام این پژوهش بررسی تاثیر استفاده از سنگچین و پوشش گیاهی بر کاهش آب‌شستگی اطراف تکیه‌گاه پل می‌باشد. به همین منظور در 30 آزمایش در سه گروه، از دو ابزار سنگ‌چین و پوشش گیاهی به صورت جداگانه و همزمان برای کنترل آب‌شستگی تکیه‌گاه مستطیلی 90 درجه و مستطیلی با دیواره‌های دایره‌ای استفاده شد. در ابتدا، آزمایش‌های سنگ‌چین انجام شد. در این آزمایش‌ها سنگ‌چین تیزگوشه در قطرهای 2.7، 6.81 و 12 میلی‌متر و چگالی 2.65 مورد استفاده قرار گرفت. ضخامت لایه سنگ‌چین دو برابر قطر متوسط سنگ-چین، چیدمان مستطیلی و هم‌تراز با مصالح بستر در نظر گرفته شد و نتایج نشان داد که سنگ‌چین با قطر 12 میلی‌متر آبشستگی اطراف تکیه‌گاه مستطیلی را 85 درصد و اطراف تکیه‌گاه مستطیلی با دیواره‌های دایره‌ای را 53 درصد کاهش داد. در مرحله دوم آزمایش‌های‌ پوشش گیاهی انجام شدند و پوشش گیاهی برای هر دو تکیه‌گاه تحت آرایش شطرنجی، در سه درصد تراکم 0.64، 1.19 و 2.8، انعطاف‌پذیر و مستغرق انتخاب شد. مطابق نتایج حاصله، درصد تراکم 1.19 برای هر دو تکیه‌گاه بهترین عملکرد را داشته و آب‌شستگی را در اطراف تکیه-گاه مستطیلی 90 درجه 84 درصد و مستطیلی با دیواره‌های دایره‌ای 81 کاهش داد. در آخرین مرحله از آزمایش‌ها، تاثیر همزمان سنگ‌چین و پوشش گیاهی بررسی شد. سنگ‌چین با قطر 6.81 میلی‌متر و پوشش گیاهی با درصد تراکم 1.19 درصد بهترین نتیجه را داشته به گونه‌ای که آب‌شستگی در اطراف تکیه‌گاه مستطیلی 93 درصد و اطراف تکیه‌گاه مستطیلی با دیواره‌های دایره‌ای را 68 درصد کاهش داد.

laboratory investigation of the effect of using riprap and vegetation on the scour around the bridge abutment

introduction one of the most important factors of damage and failure of hydraulic structures is the occurrence of local scouring around them. scour is a natural phenomenon that occurs due to the flow of water in rivers and streams. if a hydraulic structure such as a bridge pier or abutment is placed against the flow of water, the flow pattern near the structure changes and causes scouring phenomenon locally around these structures.to control scouring around the bridge abutments, various methods have been proposed, which are generally divided into two categories: flow pattern modification methods and bed protection methods. among the substrate protection methods that have been examined in this research is the use of riprap and vegetation, because riprap and vegetation are both fully available and inexpensive tools for protecting the base and abutment of the bridge are known to be washed away.methodology the experiments were carried out in the hydraulics and water structures research laboratory of the water engineering department of shahid bahonar university of kerman. in this study, two 90-degree rectangular abutment and a rectangular abutment with circular walls were used, both are galvanized with 10 cm long, 45 cm high and 6 cm wide dimensions (the abutment which is perpendicular to the flow was chosen as the width of the abutment). a long-term refrence test has done during 12 hours at a flow rate of 34 liters per second for each of the abuments, the equilibrium time was estimated to be 5 hours. after the refrence test for each of the abutments, it was observed that the maximum scour depth around the 90-degree rectangular abutment was 1.01 and the rectangular abutment with circular fins was 0.36. it should be noted that the numbers are dimensionless compared to the length of the abutment.generally, the purpose of the present study is to reduce erosion by means of two protection tools, riprap and vegetation around the bridge abutment, and for this purpose, during 30 tests and in three categories, the effect of using two riprap tools and vegetation has been investigated separately and at the same time to control the scouring of 90 degree rectangular and rectangular abutment with circular walls. in the first group of experiments, riprap tests were performed, where riprap while sharp-edged were used in three diameters of 2.7, 6.81 and 12 mm and density of 2.65. the thickness of the riprap layer is twice the average diameter of the stone, with a rectangular arrangement and parallel to the bed material. in the second stage, the vegetation tests were performed and the vegetation was selected for both abutments under a checkerboard arrangement, in three density percentages of 0.64, 1.19 and 2.8, flexible and submerged. in the last stage of the experiments, the simultaneous effect of stonework and vegetation was investigated.