EVALUASI METODE PENGGALIAN, SISTEM PENYANGGA, DAN RASIO BIAYA-MANFAAT PENGGALIAN TEROWONGAN TANJU DI KABUPATEN DOMPU, NUSA TENGGARA BARAT

EDDEN UMAGA DINATA, Ir. I Gde Budi Indrawan, S.T.,M.Eng.,Ph.D.,IPM. ; Dr.rer.nat. Ir. Arifudin Idrus, S.T.,M.T., IPU

2022 | Tesis | MAGISTER TEKNIK GEOLOGI

Bendungan Tanju berada di Sungai Tanju dan secara administratif berada di Kabupaten Dompu, NTB. Bendungan ini dibangun di kawasan Jaringan Irigasi Rababaka Kompleks. Untuk mengatasi kekurangan suplai air dari Sungai Tanju, Bendungan Tanju direncanakan mendapatkan suplai air tambahan dari Sungai Rababaka. Berdasarkan pertimbangan kondisi topografi dan geologi, sistem suplesi interbasin di Rababaka Kompleks tidak hanya berupa saluran terbuka, namun juga terowongan. Terowongan Tanju merupakan terowongan sistem suplesi interbasin di Rababaka Kompleks. Dalam penelitian ini dilakukan pemetaan geologi dan geologi Teknik. Pengamatan dan analisis massa batuan dengan metode GSI atas permukaan dan bawah permukaan, dan RMR (Rock Mass Rating), serta analisis stabilitas lereng menggunakan metode CFC, Limit Equilibrium Method (LEM) dan Finite Element Method (FEM). Dalam penelitian ini juga dilakukan analisa manfaat biaya (Benefit Cost Ratio). Kondisi di daerah penelitian merupakan perbukitan dan punggungan yang memanjang dengan arah relatif timur laut barat daya, dengan panjang punggungan sekitar 2,2 km dan memiliki elevasi puncak 325 m. Morfologi disekitar lokasi cukup terjal dengan sudut 35 derajat sampai 55 derajat. Terowongan Tanju tersusun atas tiga satuan batuan yaitu satuan andesit, breksi tuf dan endapan koluvial. Metode penggalian yang tepat untuk kedua section Inlet dan Outlet dengan kondisi batuan andesit adalah drill and blast method, penggalian seluruh muka bidang. Mengingat diameter terowongan kecil, perkerjaan drilling menggunakan alat berat jumbo dril, pekerjaan scaling menggunakan alat berat Twin Header, pekerjaan hauling menggunakan alat berat schaef loader dan dump truck kapasitas 4 meter kubik. Sehingga didapatkan waktu produksi lebih cepat 95 hari dari rencana awal. Nilai RMR dari Terowongan Tanju adalah 65 yang dapat diklasifikasikan sebagai good rock seperti pada table klasifikasi RMR, masuk pada sistim penyangga terowong (Tunneling Support System) Type II dengan mempergunakan rock bolting diameter 25 mm, L = 3 m, spasi = 2 m, shotcrete 5.0 cm. Analisis kestabilan lereng dilakukan pada bagian inlet dan outlet terowongan. Berdasarakan hasil analisis kestablian lereng didapatkan angka keamanan (critical SF) yang semuanya diatas SF ijin yang berarti semua desain rencana dapat dilaksanakan. Hasil Analisa manfaat biaya penggalian Terowongan Tanju dengan metode drill and blast nilai manfaat-biaya (B/C) = 1.22 dimana nilai (B/C) > 1. Kata kunci: Andesit, GSI, RMR, drill and blast method, manfaat biaya

Tanju Dam is located on the Tanju River and is administratively located in Dompu Regency, West Nusa Tenggara. This dam was built in the area of the Rababaka Irrigation Network. To overcome the lack of water supply from Tanju River, the Tanju Dam is planned to get additional water supply from the Rababaka River. Based on the consideration of topography and geological conditions, the interbasin supplementation system in Rababaka Complex is not only an open channel, but also a tunnel. Tanju Tunnel is an interbasin supplementary system tunnel in the Rababaka Complex. In this research, geological mapping and engineering geology were carried out. Observation and analysis of rock mass using the GSI method above and below the surface, and RMR (Rock Mass Rating), as well as slope stability analysis using the CFC, Limit Equilibrium Method (LEM) and Finite Element Method (FEM) method. In this study also conducted a cost benefit analysis (Benefit Cost Ratio). Conditions in the study area are hills and ridges that extend in a relatively northeast-southwest direction, with a ridge length of about 2.2 km and a peak elevation of 325 m. The morphology around the location is quite steep with an angle of 35 degree until 55 degree. The Tanju Tunnel is composed of three rock units, namely andesite, tuff breccia and colluvial deposits. The appropriate excavation method for both the Inlet and Outlet sections with andesite rock condition is the drill and blast method, excavating the entire face of the plane. Considering the small diameter of the tunnel, drilling work using jumbo drill machines, scaling work using Twin Header machines, hauling work using schaeff loaders and dump trucks with a capacity of 4 cubic meters. So that the production time is obtained 95 days faster than the initial plan. The RMR value of Tanju Tunnel is 65 which can be classified as good rock as shown in the RMR classification table, included in the Tunneling Support System Type II using rock bolting with a diameter of 25 mm, L = 3 m, spacing = 2 m, shotcrete 5.0 cm. Slope stability analysis was carried out at the inlet and outlet sections of the tunnel. Based on the results of the slope stability analysis, it is obtained that the critical SF is above the allowed, which means that all the design plans can be implemented. The results of the cost-benefit analysis of Tanju Tunnel excavation using drill and blast method, the cost-benefit value (B/C) = 1.22 where the value (B/C) > 1. Keywords: Andesite, GSI, RMR, drill and blast method, cost benefit

Kata Kunci : Andesite, GSI, RMR, drill and blast method, cost-benefit