EVALUASI STABILITAS BENDUNG (Studi Kasus Bendung Tegal di Sungai Opak Hilir, Kabupaten Bantul)

FEBRIANTI SILVIANA DEWI , Prof. Dr. Ir. Fatchan Nurrochmad, M. Agr

2016 | Skripsi | S1 TEKNIK SIPIL

Bendung Tegal merupakan bendung yang melintang di Sungai Opak Hilir, dibangun pada tahun 1997, dan memiliki luas daerah irigasi 678 Ha. Kondisi debit aliran sungai yang tidak menentu dan terjadinya gempa membuat beberapa bagian bendung rusak. Kerusakan Bendung Tegal yang sangat terlihat adalah menurunnya elevasi kolam olak dengan persentase kolam olak yang rusak 37,27%. Kolam olak yang terus-menerus rusak dikhawatirkan dapat mengakibatkan keruntuhan pada tubuh bendung. Evaluasi bangunan eksisting dilakukan untuk mengetahui stabilitas bendung terhadap bahaya yang ada. Perancangan ulang bendung dilakukan jika dimensi bendung eksisting sudah tidak stabil. Evaluasi bendung menggunakan debit banjir rancangan 949,9 m3/s. Perancangan ulang Bendung Tegal menggunakan debit banjir rancangan terbaru 100 tahunan, yaitu 1075,64 m3/s. Metode pengumpulan data yang digunakan untuk evaluasi dan perancangan ulang bendung tegal adalah metode dokumentasi, observasi, dan literatur. Analisis tinggi muka air hulu-hilir, gaya vertikal, horizontal, dan momen dilakukan setelah semua data terkumpul. Analisis kolam olak pada bendung eksisting menggunakan tipe Vlugter, sedangkan perancangan ulang bendung menggunakan USBR III. Dimensi bendung eksisting maupun hasil perancangan ulang dilakukan kontrol rembesan dan stabilitas bendung. Stabilitas bendung meliputi guling, geser dan kuat dukung tanah. Kontrol stabilitas bendung akan menghasilkan angka aman yang memperkirakan kondisi bangunan stabil atau tidak. Hasil evaluasi bendung eksisting menunjukkan bahwa dimensi bendung eksisting tidak mampu menahan gaya geser, terutama saat kondisi air banjir dan air normal dengan gempa. Stabilitas bendung eksisting aman terhadap bahaya guling dan memenuhi syarat kuat dukung tanah. Perancangan ulang Bendung Tegal dilakukan dengan hasil bahwa dimensi bendung redesain aman terhadap bahaya guling, geser, dan memenuhi syarat kuat dukung tanah.

Tegal Dam was built in Opak Hilir River in 1997. Tegal Dam had 678 Ha of irrigation area. The discharge was always flactuative, so it made dam easily to fail in some parts. Stilling basin of Tegal Dam was broken 37,27%. Such damage could reduce the stabilities of dam. Evaluation of dam was done to predicate the stability of sliding, overturning, and soil bearing capacity. Redesign was done if the dimension of existing dam couldn't save the stabilities. Discharge of evaluation dam was 949,9 m3/s. Redesign of Tegal Dam used 100 years of the newest design of flood discharge, 1075,64 m3/s. The method of evaluations and redesign of dam were documentation, observation, and literature. Three of method were used to collect primary and secondary datas, those were needed. Analysis of water level upstream-downstream, horizontal-vertical force, and momen were done after all of data was collected. Stilling basin in Tegal Dam was analyzed with Vlugter. Stilling basin in Tegal Dam should be done rehabilitation with USBR III. Dimensions of the existing dam and the results of the redesign were done piping and stabilities control of dam. The stabilities of dam were shear force, overturning, and soil bearing capacity. Control stabilities of dam gave safety factor, that was prediction of dam. The dam was still safe or not. The results of dam evaluation prove that dimension of dam weren't able to withstand sliding, especially when the water conditions were normal with earthquake and flooding. Stability of existing dam was safe from overturning and soil bearing capacity. The results of redesign dam proved that dimension of dam was safe from overturning, sliding, and soil bearing capacity.

Kata Kunci : Bendung Tegal, Vlugter, USBR III, evaluasi stabilitas, perancangan ulang