Kajian gerusan lokal di sekitar abutmen jembatan dan upaya pengendaliannya dengan tirai

SUSILOWATI, Rini, Dr.Ir. Bambang Agus Kironoto

2005 | Tesis | S2 Teknik Sipil

Gerusan lokal (local scour) terjadi karena pola aliran lokal di sekitar bangunan sungai sebagai akibat sistem pusaran (vortex system) yang timbul karena aliran dirintangi oleh abutmen. Penelitian ini bertujuan untuk mempelajari gerusan lokal di sekitar abutmen jembatan dan pengaruh pengendalian gerusan lokal di sekitar abutmen jembatan dengan tirai. Penelitian dilakukan pada saluran dengan kemiringan 0,0003 m, kondisi aliran live-bed scour, Q = 5,69 liter/detik, dan Do = 7,5 cm. Tipe abutmen yang dipakai adalah wing-wall abutment (WW) dengan dimensi lebar abutmen, LA = 0,0375 m, panjang muka bawah, L = 0,15 m, panjang muka atas, L = 0,08 m dan tinggi H = 0,30 m. Model pengendalian gerusan berupa tirai yang ditempatkan di hulu abutmen dengan variasi susunan tirai zigzag dua dan lurus memanjang; jarak spasi antar as tiang tirai 0,2 LA atau 0,4 LA; jarak as tirai ke as abutmen 4 LA atau 6 LA; tinggi tirai 0,2 Do, 0,6 Do, 0,8 Do, atau DMA. Hasil penelitian menunjukkan bahwa variasi tirai berpengaruh terhadap kedalaman gerusan di sekitar abutmen. Didapatkan T2S1X1H4 (susunan tirai lurus memanjang; jarak spasi antar as tiang tirai 0,2 LA; jarak as tirai ke as abutmen 4 LA; tinggi tirai DMA) menghasilkan rata-rata kedalaman gerusan pada kondisi kesetimbangan yang nilainya paling kecil dibanding tirai lainnya, yaitu DS/LA sebesar 1,63 dengan reduksi sebesar 22,01 %, serta mampu mereduksi degradasi melintang pada posisi di sebelah hulu abutmen sebesar 0,6 cm atau ±5,38%. Tipe wing-wall abutment (WW) tanpa proteksi (LA = 0,0375 m) memiliki kedalaman gerusan lebih besar dibandingkan tipe spill-through abutment (ST) tanpa proteksi (LA = 0,15 m) pada posisi titik kedalaman gerusan maksimum dengan kondisi aliran live-bed scour.

Local scour occurs because local flow pattern around the river building as a consequence of vortex system that emerges because flow is restricted by abutment. Research aims to study local scour around the bridge abutment and the influence of local scour control around bridge abutment with pile groups. Research conducted in flume with slope 0.0003 m, live-bed scour flow condition, Q = 5.69 l/s and, Do = 7.5 cm. Type of abutment used is wing-wall abutment (WW) with abutment width dimension, LA = 0.0375 m, bottom front length, L = 0.15 m, top front length, L = 0.08 m and height H = 0.30 m. Scour control model is pile groups placed at the upper of abutment with pile groups composition variation are two zigzag and straight; the space distance between pile groups pole either 0.2 LA or 0.4 LA; the distance of pile groups axis to abutment axis either 4 LA or 6 LA; the height of pile groups varies 0.2 Do, 0.6 Do, 0.8 Do, or DMA. Research results show that pile groups variation has influence on the scour depth around abutment. It is found T2S1X1H4 (pile groups composition straight, the space distance between pile groups pole axis is 0.2 LA, the distance of pile groups axis to abutment axis is 4 LA and the height of pile groups DMA) results the smallest score of equilibrium scour depth average than the other type of pile groups, DS/LA that is 1.63 with the value of reduction is 22.01 %, and also able to reduce degradation at the upper of abutment 0.6 cm or ± 5.38 %. Wing-wall abutment (WW) type non protection (LA = 0.0375 m) has scour depth bigger than spill-through abutment (ST) type non protection in the maximum scour depth point with live-bed scour condition.

Kata Kunci : local scour, live-bed scour, equilibrium scour depth, pile groups variation, abutment, gerusan lokal, live-bed scour, kedalaman gerusan pada kondisi kesetimbangan, variasi tirai, abutmen