KAJIAN KESTABILAN LERENG DENGAN METODE SLOPE MASS RATING (SMR) DI AREA GENANGAN BENDUNGAN TUGU, KABUPATEN TRENGGALEK, PROVINSI JAWA TIMUR
ALYA SAFITRI, Hendy Setiawan, S.T., M.Eng., Ph.D
2020 | Skripsi | S1 TEKNIK GEOLOGIBendungan Tugu terletak di Desa Nglinggis, Kecamatan Tugu, Kabupaten Trenggalek, Jawa Timur. Bendungan ini dibangun membendung Sungai Keser. Tujuan pembangunannya yaitu untuk meminimalisir terjadinya banjir, untuk irigasi, penyedia kebutuhan air baku, sebagai area pariwisata dan sumber tenaga listrik. Berdasarkan stratigrafi regional, daerah penelitian termasuk dalam Formasi Mandalika. Terdapat struktur geologi regional berupa sesar geser yang diperkirakan memotong area bendungan. Penelitian ini dilakukan untuk mengetahui tingkat kestabilan lereng area genangan bendungan. Penentuan tingkat kestabilan lereng dilakukan dengan metode SMR (Slope Mass Rating) berdasarkan karakteristik geologi teknik dan pengklasifikasian kualitas massa batuan berdasarkan GSI (Geological Strength Index). Dalam analisis SMR (Slope Mass Rating) penentuan tipe runtuhan lereng dilakukan berdasarkan analisis kinematika.Karakteristik geologi teknik daerah penelitian meliputi aspek geomorfologi, geologi, struktur geologi dan hidrogeologi. Berdasarkan aspek geomorfologi daerah penelitian tersusun atas satuan geomorfologi perbukitan struktural berlereng curam dan satuan endapan aluvial. Daerah penelitian tersusun atas satuan breksi vulkanik, lava andesit, endapan koluvial dan endapan aluvial. Struktur geologi daerah penelitian yaitu berupa sesar geser diperkirakan dan kekar ekstensi yang diamati langsung di lapangan. Kedalaman muka air tanah daerah penelitian diperkirakan berkisar 15-70 meter di bawah permukaan tanah. Kualitas massa batuan daerah penelitian berdasarkan klasifikasi GSI terdiri atas batuan kualitas sedang (GSI 36-55), batuan kualitas buruk (GSI 21-35) dan batuan kualitas sangat buruk (GSI <20). Analisis kinematika menunjukan bahwa tipe runtuhan lereng yang mungkin terjadi di area genangan bendungan adalah wedge failure dan toppling failure. Dalam analisis tingkat kestabilan lereng berdasarkan SMR daerah penelitian tersusun atas lereng stabil (SMR 61-80), lereng stabil sebagian (SMR 41-60), lereng tidak stabil (21-40), dan lereng sangat tidak stabil (SMR 0-20). Berdasarkan hasil analisis SMR, lereng stabil hingga stabil sebagian dominan berada pada lereng area genangan bagian utara hingga hulu bagian utara, sedangan lereng yang tidak stabil hingga sangat tidak stabil dominan berada pada lereng area genangan bagian selatan hingga ke hulu bagian selatan.
Tugu Dam is located at Nglinggis Village, Tugu District of Trenggalek Regency, East Java Province. This construction was built to dam the Keser River. The purpose of its development is to provide irrigation and raw water, as a tourism area and a micro - hydro power plant. Based on regional stratigraphy, the research area is located on the Mandalika Formation. While the dam construction is intersected with the estimated regional fault. This research aim to analyse the stability of the reservoir slope area through Slope Mas Rating (SMR) method and based on engineering geological characteristics. Classification of rock mass quality performed based on Geological Strength Index (GSI). The determination of the slope collapsing types is based on kinematic analysis. The engineering geological characteristics include geomorphological, geological, structural geological and hydrogeological aspects. The geomorphological condition of the research area mainly formed as the alluvial plain and structural hills with steep slopes. The lithological conditions consist of volcanic breccia, andesitic lava, colluvium and alluvium sedimentation. The geological structure of the research area formed as a dextral shear fault estimated in 2019 according to secondary data and fracture. The depth of ground water level is estimated to 15-70 meters below the surface. The rock mass quality of the research area based on GSI classification consist of medium quality rock (GSI 36-55), poor quality rock (GSI 21-35) and very poor quality rock (GSI <20). The kinematic analysis shows that the types of slope failure that may occur in the reservoir slope are wedge failure and toppling failure. The slope stability analysis results implied that the slope of the dam reservoir consists of stable slopes (SMR 61-80), partially stable slopes (SMR 41-60), unstable slopes (21-40), and very unstable slopes (SMR 0-20). According to the SMR result, the stable and partially stable slope are dominantly found on the northern side of the reservoir, while the unstable and very unstable slope are found on the southern side of the reservoir.
Kata Kunci : Slope Mass Rating (SMR), Analisis Kinematika, Geological Strength Index (GSI), Karakteristik Geologi Teknik, Area Genangan Bendungan
