Pier sediment scour tests for Merrill-Barber Bridge final report

Abstract

The objectives of this study were 1) to determine the maximum structure-induced local sediment scour depths for the proposed bridge piers for the Merrill Barber Bridge over Indian River on.State Road 60 in Indian River County, Florida and 2) to determine the feasibility of predicting equilibrium local scour depths near complex multiple pile bridge piers from bottom shear stresses on the prescoured bed. A series of hydrodynamic tests were conducted in a laboratory flume (100 ft long x 8 ft wide x 2 ft deep) where flow velocities near model piers were measured with a two component constant temperature anemometer at a height of 3 mm above the bed. Bottom shear stresses were then estimated from the flow measurements. The piers (which are 1/15 scale models of proposed Merrill Barber Bridge piers) consisted of thirtysix square piles (3 columns of 12) and a pile cap that was positioned at different elevations above the bottom. Two different pile cap shapes were also considered. A simple relationship between the prescoured bottom shear stress and the equilibrium local scour depth was postulated. Sediment scour tests were then conducted in the same flume with the same models. The average duration of these tests was 28 hours. Scour depths were measured periodically throughout these tests using an acoustic transponder. The scour measurements were used 1) to establish the maximum scour depths for the Merrill Barber Bridge piers and 2) to calibrate and test the scour-shear stress relationship. Even though the range of conditions tested was somewhat limited, the approach appears promising and should be pursued further. A number of interesting findings were made regarding the rate at which scour occurs in these complex structures. (Document contains 134 pages.