ANALISIS STABILITAS SISTEM FONDASI HYDROPOWER PLANT PADA SUNGAI BAWAH TANAH ZONA KARST

Sulha, Dr. Ir. Ahmad Rifa’i, MT

2013 | Tesis | S2 Teknik Sipil

Kondisi topografi dan geologi Kabupaten Gunung Kidul merupakan pegunungan karst dan memiliki akuifer air tanah yang sangat dalam. Kemampuan tanah yang kurang baik dalam menyerap dan menyimpan air menjadikan masyarakat kesulitan memenuhi kebutuhan air bersih. Potensi sumber daya air di wilayah ini cukup besar khususnya di Goa Seropan berupa aliran air sungai bawah tanah. Pemanfaatan air bawah tanah Goa Seropan selain untuk bahan baku air bersih juga sebagai penggerak turbin. Turbin menghasilkan energi listrik untuk mengangkat air bawah tanah ke permukaan. Perencanaan lokasi dan tipe konstruksi sistem fondasi hydropower plant menjadi jawaban permasalahan kekurangan air bersih di wilayah tersebut. Tinjauan penelitian yakni analisis sifat teknis batuan dan stabilitas sistem fondasi. Dalam penelitian ini, analisis menggunakan metode elemen hingga model plan strain dengan bantuan Software PLAXIS v8.2. Pendekatan analisis dilakukan pada tampang fondasi dengan menggunakan 4 model geometri. Variasi dimensi model geometri terhadap pelat horisontal yakni 0,40 meter dan 0,45 meter, dinding vertikal yakni 0,30 meter dan 0,35 meter, dan bored pile yakni 0,20 meter, 0,25 meter dan 0,30 meter. Material properties di lokasi konstruksi diambil dari hasil penelitian dan uji laboratorium IWRM Goa Seropan dan Tim Teknis UGM. Input gemoteri dari data pengukuran lapangan yang disederhanakan, sedangkan input parameter tanah, batuan dan beton dari data sekunder. Analisis model yakni beban statis dan dinamis menggunakan Software PLAXIS v8.2 yang divalidasi berdasarkan perhitungan manual. Hasil simulasi numeris menunjukkan penambahan bored pile 0,20 meter pada sistem fondasi hydropower plant mampu melawan tegangan yang terjadi di tanah dasar akibat beban gempa dengan faktor aman sebesar 2,01. Sistem fondasi sesuai dengan model geometri I dengan dimensi pelat horisontal = 0,40 meter, dinding vertikal = 0,30 meter, dan bored pile = 0,20 meter cukup aman dan stabil terhadap beban statik maupun dinamik. Selisih diplacement vertikal maksimum dua titik fondasi sesuai model gemetri I akibat akumulasi pembebanan menyebabkan angular distortion sebesar 0,2159 cm atau 1/1112 masih relatif kecil dari angular distortion izin yakni 1/750. Simpangan horisontal maksimum fondasi dan bangunan yang terjadi akibat beban gempa 355,4g sebesar 0,379% masih relatif aman jika ditinjau terhadap simpangan izin sebesar 1,54%. Software PLAXIS terbukti mampu memodelkan perilaku dinding goa dan struktur yang memikul beban statik dan dinamik dengan cukup baik

Topographically and geologically, Gunung Kidul Regency is a mountainous karst and has very deep aquifers and groundwater. The soil condition is hard to absorb and store water, this condition makes people hard to fulfill their fresh water need. This area has a big water resource potential, especially in Goa Seropan, in this area, the water resource comes out the underground river. Goa Seropan water resource is utilized not only to fulfill the daily needs but also to run the turbine. Turbine produces electrical energy to absorb water. Determining both location and construction type of hydropower plant's foundation is a solution of the water resource problems in this area. This research is aimed at analysis of rock engineering properties and foundation system stability. In this study, an analysis using the element method up to model plan strains with the help of PLAXIS Software v 8.2. The approach of analysis is done on the Foundation look by using the 4 model geometry. Variations in the dimensions of the model geometry of horizontal plates namely 0.40 meters and 0.45 meters. Vertical walls, i.e. 0.30 meters and 0.35 meters, and bored pile i.e. 0.20 meters, 0.25 m and 0.30 meters. Material properties in the construction site are drawn from the results of research and test laboratory of IWRM Goa Seropan technical team and the University of Gadjah Mada. Input data from field measurements geometry simplified, whereas input parameters of soil, rock and concrete from secondary data. Model analyses of the static and dynamic loads using the PLAXIS Software v 8.2 are validated based on the manual calculations. Results of the numerical simulation showed that the addition of bored pile for 0.20 meter on foundation system hydropower plants able for resisting stresses occur in the land base as a result of the earthquake loads by a factor of safety of 2.01. The Foundation system in accordance with the model geometry I with horizontal plate dimensions = 0.40 m, vertical wall = 0.30 m, and bored pile = 0.20 m is safety enough and stable toward static or dynamic load. The difference in displacement vertical maximum two point of foundations according to the geometry model of I. from all of loads will cause angular distortion for 0,2159 cm or 1/1112 is still relatively small angular distortion of permission i.e. 1/750. Maximum horizontal distortion foundations and buildings due to earthquake loads 355, 4 g for 0,379% is still relatively safe if it’s reviewed against allowable distortion amounting to 1.54%. PLAXIS Software proved to be able to model the wall behaviour of cave and structure of which bearing the burden of a static and dynamic quite well.

Kata Kunci : batuan karst, fondasi mesin, simulasi numeris, beban dinamis