Author(s): Abhi Sangra; Manish Mall; K. S. Hari Prasad; C. S. P. Ojha

Linked Author(s): ABHI SANGRA

Keywords: Scour depth; Bouldery strata; Live-bed scour; Critical velocity; IITR-BRO method

Abstract: Accurate prediction of local scour in rivers with bouldery strata is crucial for the safe design of bridge foundations. Traditional methods often overestimate scour depth in non-cohesive, bouldery beds, leading to overly conservative designs. This study introduces a new empirical approach for predicting local scour depth (d_se), based on analysis of model and prototype data from four bridges -- Passighat, Sisseri, Lohit (Arunachal Pradesh), and Dhoondi (Himachal Pradesh) -- in collaboration with the Border Roads Organisation. The proposed IITR-BRO method calculates scour depth as a function of flow velocity (V) and the critical velocity (Vc), which represents the point at which sediment movement begins. The empirical relationship used considers the difference between flow velocity and critical velocity, adjusted by a factor that incorporates bed conditions and other variables. This factor is determined using empirical relationships based on bed material size and flow depth. The IITR-BRO method also includes correction factors to enhance the accuracy of scour depth predictions, considering factors such as pier shape, flow angle, and bed conditions. Comparative analysis with existing methods for circular piers indicates that the IITR-BRO approach yields more accurate predictions for live-bed scour when the flow velocity exceeds the critical velocity. However, it may overestimate scour depth in clear-water conditions, where flow velocity is below critical levels, sometimes resulting in unrealistic values. In such cases, the HEC-18 method has proven to be more suitable for predicting clear-water scour scenarios. The findings suggest that the proposed equation, effective for boulder sizes up to 300 mm, provides a practical solution for scour prediction in rivers characterized by large boulders, facilitating more efficient bridge designs without compromising safety, especially in areas with variable sediment sizes.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1845-cd

Year: 2025