Kajian pengendalian gerusan di sekitar abutmen jembatan pada kondisi adanya angkutan sedimen

ABDURROSYID, Jaji, Dr.Ir. H. Bambang Agus Kironoto

2004 | Tesis | S2 Teknik Sipil

Gerusan adalah proses semakin dalamnya dasar sungai karena interaksi antara karakteristik aliran dengan karakteristik material dasar sungai. Secara kenyataan di lapangan, gerusan yang terjadi pada abutmen jembatan adalah merupakan gerusan total, yaitu kombinasi antara gerusan local, gerusan umum dan gerusan akibat penyempitan/terlokalisir. Penelitian ini bertujuan untuk mengetahui pengaruh penempatan plat (collar), tirai (screen) dan groundsill terhadap proses gerusan dan kedalaman gerusan yang terjadi di sekitar abutmen, pada kondisi adanya angkutan sediment (live-bed scour). Penelitian ini dilakukan dengan menggunakan sediment recirculation flume dengan panjang 10 m, lebar 0,60 m dan tinggi 0,45 m dengan kondisi aliran permanen seragam (quasi steady-uniform flow). Model abutmen adalah tipe spill-trough (ST) dengan dimensi lebar abutment, Lb = 0,15 m, panjang, L = 0,50 m dan tinggi H = 0,45 m. Model pengendalian gerusan berupa variasi pelat, variasi tirai dan variasi jarak groundsill. Pada penelitian ini diambil aspect ratio (perbandingan lebar terhadap kedalaman aliran, B/h0) 2,1

Scouring is the process of progressively depth of river bed, because of interaction between river’s stream characteristics and the bed materials river characteristic. In fact, scouring which happened on bridge abutment representing the total scour, that combine among local scour, general scour and constriction or localized scour. This research is aimed to know the influence of plate location (collar), screen and groundsill in the process of scour and the scour depth that happened around abutment, in condition of existence the sediment transport (live-bed scour). The research done by using sediment recirculation flume with 10.0 m long, 0.60 m width and 0.45 m height in the quasi steady- uniform flow. The model of abutment which used was spill-trough type (ST), the dimensions of abutment was Lb = 0.15 m width, L = 0.50 m long and H = 0.45 m height. The models of scouring control consist of plate variation, screen variation and groundsill at distances variation. In this research taken range of aspect ratio (the ratio width on depth of flow, B/h0) 2.1< B/h0<6.9. The depth of scouring around abutment measured in every running, for six hours and on seven observing position. The depth of scouring with protection measured in condition of flow live-bed scour without sediment supply. Result of research indicate that the condition of live-bed scour without sediment supply is the most critical condition. It means that the scour depth have larger condition than the condition of clear-water scour and live bed scour with sediment supply. The location of screen of type T4a in upriver abutment, at optimum distance 4 Lb (Lb = wide of abutment bed) from ace abutment gives the biggest total scour depth 50.98 %. The location of Groundsill G4 in downstream abutment, at optimum distance 5 Lb from ace abutment gives the biggest total scour depth 22.28 %. The reduction of local scour is equal to 25.45 % and the reduction of general scour (degradation) is equal to 93.22 %. The location of the plate type P1c in around the abutment body can reduce 12.79 % from the biggest total scour. The ability of the plate for reduce the scour reach the maximum range when the distance of plate to channel bed is zero, and the width of optimum plate at b = 0.2 Lb, and also form the plate encircle the body abutment. The structure location of scour controller which is in the form of combination K3, which is combination between type screen T4a and groundsill G4 can reduce the biggest total scour around 35.66 %; Combination K1 which is consist of type plate P1c, type screen T4a and groundsill G4, have reduce of equal to 35.07 %; Combination K2 which is consist of type plate P1c and groundsill G4, have the smallest discount value 3.82 % among those combination type. In general, the scour pattern happened around abutment, caused by with or without protection is same, this is shown by form of scour contour which is relatively same. The form of scour is wide up at the side of abutment (perpendicular to the stream) and lengthen up at downstream with the shallower scour depth.

Kata Kunci : Hidrologi,Pola Gerusan,Plat, Tirai dan Groundsill,Angkutan Sedimen, scour depth, clear-water scour, live-bed scour, scour pattern