Pengaruh Variasi Ukuran Butiran Dasar Sungai Terhadap Kedalaman Gerusan (Scouring Depth) pada Abutment Jembatan

Abstract

Local scour around the abutment is one of the main causes of decreased stability and failure of the bridge substructure. "Scour is the process of deepening the riverbed due to the interaction between flow characteristics and the characteristics of the riverbed material." This phenomenon is triggered by the formation of a vortex system due to the obstruction of the flow rate by the abutment structure. This study aims to analyze the maximum scour depth that occurs around the bridge abutment by trying variations in two riverbed grain sizes. Modeling was carried out using the HEC-RAS application using the Froehlich equation. The results showed that variations in the size of the riverbed grain greatly affect the local scour depth on the abutment. In the condition of 0.45 mm grain size, the maximum scour depth occurred at the left abutment reaching 9.58 m, while at the right abutment it was 22.71 m. In the condition of 5 mm grain size, the maximum scour depth occurred at the left abutment reaching 8.04 m, while at the right abutment it was 21.17 m. The difference in scour depth between the two sides is influenced by the size of the riverbed grains at the foot of the Abutment. Because the characteristics of the riverbed sediment are in the form of fine sand (D₅₀ = 0.45 mm) which has a small critical shear stress, the eddy current very easily erodes and washes away the base material around the bridge foundation and in the form of gravel (D₅₀ = 5 mm) which has a greater critical shear stress, the eddy current has been reduced to erode and wash away the base material around the bridge foundation.