Kajian penggunaan Tirai sebagai upaya pengendalian gerusan di sekitar pilar jembatan di sungai

SAFITRI, Yulia Eka, Dr.Ir. Bambang Agus Kironoto

2005 | Tesis | S2 Teknik Sipil

Penyempitan pada aliran sungai akibat keberadaan bangunan yang menghalangi, seperti krib, pilar maupun abutment jembatan, dapat merubah pola aliran sungai yang akan menyebabkan terjadinya gerusan lokal dan menyebabkan penurunan elevasi yang cukup signifikan di sekeliling pilar dan mengganggu stabilitas struktur pilar tersebut. Penelitian tentang pola gerusan lokal di pilar jembatan dengan variasi tirai dilakukan untuk mempelajari pola gerusan yang terjadi dan mengetahui efektifitas tirai dalam mengurangi kedalaman gerusan. Penelitian gerusan lokal di sekitar pilar dan penanganannya dilakukan di laboratorium pada kondisi live-bed scour dengan aliran seragam (steady uniform flow), debit Q = 0,00321 m3/det, kedalaman Yo = 0,075 m, kemiringan saluran So= 0,0003. Model pilar yang digunakan berbentuk rectangular with semi circular nose dengan dimensi 4 cm untuk lebar dan panjang 12 cm (1:3) dan tinggi pilar 45 cm. Model yang dipakai untuk pelindung gerusan sebelah hilir adalah groundsill yang dipasang pada jarak 60 cm dari as pilar sedangkan sebelah hulu diberi tirai dengan variasi jarak 3b, 3,5b, 4b, 4,5b (b = lebar pilar) dari as pilar, variasi tinggi tirai 0,2Yo, 0,6Yo, 0,8Yo, tirai dengan tinggi di atas muka air. Untuk setiap kali running pengamatan dilakukan selama 120 menit. Dari hasil penelitian diperoleh bahwa penempatan tirai T1S4A4 (tirai dengan jarak antar as tirai 0,3b, jarak terhadap as pilar 4,5b dan tinggi tirai diatas muka air) dapat mereduksi kedalaman gerusan 23,1%.

The existance of an obstructor in the river flow for instance groyne, pier, or bridge abutment could change the flow pattern. This such condition could cause the significant decrement in the elevation around the pier and also can disturb the stability of pier structure. This reserach was carried out to investigate pattern of local scour and the efectiveness of screen in reducing the scour depth. The research on local scour around the pier was held in laboratorium by using experimental model. There are some conditions used in this model, they are live-bed scour condition with steady uniform flow, the flow rate (Q) was 0.00321 m3/s, the depth of the flow (Yo) was 0.075 m, the inclination of the channel (So) was 0.0003. The pier model that was used has rectangular shape with semi circular nose, the dimension was 4 cm for the wide, 12 cm for the length (1:3) and 45 cm for the height of the pier. Groundsill was used to cover the pier from scouring at the lower side, it was placed at distance of 60 cm from the pier axis. Meanwhile, the screen was used to cover the upper side with some distance variations. They are 3b, 3.5b, 4b, and 4.5b (b is the width of the pier) from the axis of the pier. The variations of the height of the pier are 0.2Yo, 0.6Yo, 0.8Yo, 1.2Yo (the geight level of the screen was above the water surface). For each of the test, the monitoring was carried out for 120 minutes. The result of the research showed that the placement of screen TIS4A4 (screen with the distance from axis to axis was 0.3b, the distance from the axis of the pier was 4.5b and the height of screen was above the water surface) could reduce the depth of the scour to 23.1%. Keywo rds : local scour, live-bed scour, depth of scour, scour reduction

Kata Kunci : Pilar Jembatan,Penggerusan,Pengendalian,Tirai