Experimental evaluation of scour reduction around oblong collar pier structure: an integrative approach

Collar pier structure (CPS) effectively reduces the rate of scouring, highlighting the importance of temporal scour depth (d_s) estimation to enhance bridge safety. A thorough literature review is conducted to collect 696 data points and equations related to oblong CPS. The key parameters, including pier length × width (L × D), collar length × width × position (L* × W × H), sediment size, and velocity, are identified on d_s and their influences are evaluated. Performing new experiments varying W and L, another 174 data points are obtained, measuring d_s at five azimuthal positions (ϕ) in a flume of 11 m long, 0.81 m wide, and 0.60 m deep, with a uniform sediment bed thickness of 0.20 m. For a pier without a collar (PWOC), the location of maximum d_s is observed upstream (ϕ = 0°), whereas with a collar (PWC), the location shifts downstream (ϕ = 135°). A maximum 93.81 % scour reduction is achieved when W/D = 3.5 and L/D = 2. Conversely, the minimum scour reduction is only 10.74 % when W/D = 1.5 and L/D = 4. Limited literature provides formulas for calculating d_s, mainly relying on restricted data. The data from previous studies are rarely utilized for conducting comprehensive analyses. A new formula for d_s is developed by applying nonlinear regression analysis combined with the Gauss-Newton optimization technique. Its efficacy is confirmed through comparison with both experimental and literature datasets using statistical evaluation metrics. This new formula shows significantly improved accuracy by 10.8–54.2 % in terms of P_in when compared to the literature formula. This research offers engineers a reliable approach for predicting d_s across different scenarios, ultimately improving bridge safety.