Physical Model Flume Study for Supporting Design of the Proposed Bangabandhu Railway Bridge Over the River Jamuna

A physical model study has been carried out at River Research Institute, Bangladesh to support the design of the proposed Bangabandhu Railway Bridge over the river Jamuna. Under the framework of the study, one flume model have been constructed to fulfil the requirements for the design of the Proposed Bangabandhu Railway Bridge. A flume model, a river reach of about 2.0 km and width about 80m have been reproduced using arbitrary plain bathymetry. The scale of Flume model is 1:80 After calibration of the the model, different application test runs are conducted with various test scenarios. A total of eight tests have been conducted for the flume study. Apart from two calibration tests, all tests are application tests. From the test results of Flume study, it is concluded that among different test alternatives, different piers experienced different scour. Maximum net scour observed from the model tests was 19.40m (-24.40 mPWD) and it occurred at proposed bridge Pier-1(Pier-19 in prototype). It was observed from the recent velocity profile in model that the upstream velocity was lessening slightly due to the sediment deposition. Furthermore, the test results showed that less scour was occurred around existing roadway bridge piers as compared to the proposed railway bridge piers since proposed piers created more turbulence. Photographic views as well as physical evidences corroborated the same facts. The key points of the test findings are given herein.

• Maximum net scour around the existing Bridge pier was found to vary within 3.20 m (+0.8 mPWD) to -10.20 m (-18.20 mPWD)
• Maximum net scour around the proposed Bridge pier was within the range of 2.60 m (+1.4 mPWD) to -19.40m (-27.40 mPWD)
• Maximum point average velocity around the Bridge pier was varied from 1.77 m/s – 5.5m/s
• Maximum proto velocity at 0.8d around proposed bridge piers ranges from 4.14 m/s to 4.52 m/s
• Maximum longitudinal extent of local scour at upstream side varies from 27 m to 28 m while at downstream side ranges from 155.0 m to 163.0 m
• Deposition observed at downstream of proposed bridge and u/s of existing bridge section

Keywords: Physical Model, Flume, River Jamuna, Bathymerty and Bangabandhu Railway Bridge