Evaluasi Stabilitas Lereng Situs Ratu Boko Berdasarkan Simulasi Numeris

UMRAN SARITA, Dr. Ir. Ahmad Rifa’i, M.T.

2013 | Tesis | S2 Teknik Sipil

Situs Ratu Boko merupakan situs sejarah yang ditetapkan UNESCO sebagai warisan budaya dunia, terletak di Kabupaten Sleman Provinsi Daerah Istimewa Yogyakarta. pembangunan fasilitas pendukung situs Ratu Boko menyebabkan perubahan geometri serta pembebanan lereng. Gempa Yogyakarta tahun 2006, terjadi instabilitas bangunan Plaza Andrawina seperti retakan balok dan kolom, dimana saat ini telah dilakukan penangan berupa kolom penyokong. Tinjauan penelitian yakni deformasi lereng, faktor aman, penyebab instabilitas bangunan serta efektifitas penangan. Dalam studi ini, analisis menggunakan metode elemen hingga model plan strain dengan bantuan software Plaxis V8.2. Model yang digunakan yakni lereng asli, setelah perubahan lereng dan pembangunan fasilitas serta setelah penanganan. Input gemoteri dan sturktur perlapisan dari data topografi dan pengamatan lapangan, sedangkan input parameter tanah, batuan dan beton dari data sekunder yang divalidasi terlebih dahulu. Analisis model yakni beban statis dan dinamis. Berdasarkan simulasi numeris, terjadi deformasi setelah adanya perubahan geometri lereng situs Ratu Boko. Akibat pembangunan fasilitas, menyebabkan peningkatan deformasi baik beban statis maupun dinamis di sekitar fondasi terluar. Hal ini terus berlanjut sampai saat penanganan berupa penggalian fondasi penyokong yang letaknya di sekitar fondasi terluar. Dilihat dari kestabilan lereng, terjadi pula penurunan faktor aman lereng sampai dengan kondisi ini yakni 1,274 dibandingkan lereng asli yakni 2,767, serta peningkatan selisih displacement kedua fondasi terluar menyebabkan jarak kedua kolom berubah seperti kondisi eksisting yakni + 3 cm. Retaknya sambungan balok dan kolom terluar seperti kondisi eksisting (1 - 2mm) akibat akumulasi displacement vertikal fondasi terluar lebih besar setelah gempa dan penggalian fondasi sehingga menyebabkan angular distorsion yakni 1/213. Setelah pemasangan kolom peyokong cukup efektif mereduksi peningkatan sebelumnya, akibat beban gempa selisih displacement kedua kolom terluar yakni 1 mm, displacement vertikal fondasi sebelah dalam lebih besar dari fondasi terluar sehingga mereduksi nilai angular distortion sebelumnya menjadi 1/148, serta menaikkan faktor aman lereng saat gempa yakni 2,489. Ditinjau dari angular distorsian, akibat beban statik nilai yang diperoleh masih relatif tinggi yakni 1/199 jika kolom penyokong dilaksanakan bersamaan pembangunan fasilitas, namun kerusakan ini termasuk ringan. Pendekatan numeris model 2D dengan software Plaxis terbukti mampu memodelkan struktur tanah serta bangunan secara bersamaan untuk mendapatkan interaksi keduanya.

The Ratu Boko Site is a historical site that might be protected its existence in Sleman regency, DI Yogyakarta province. The building of supported facilities of the Ratu Boko site caused the geometrical change and olso slope loading. Yogyakarta earthquake 2006, ocoured instability of the Plaza Andrawina building, such as beam and column crack, whereas it has carried out the rehabilitation with supported column. Research observation are slope deformation, safety factor, coused of building instability and the effectivity of rehabilitation. In this study, the analysis using finite element method with the plan strain model by the assistance of Plaxis V8.2 software. The model that is used are natural slope, after the slope change and building facilities and after rehabilitation as well. The geometry input and layer structure from topography data and field observation. While the soil parameter input, rock and concrete from secondary data which is validated before. The analysis model is static and dynamic load. In regard of numerical simulation, occurred the deformation after the change of geometrical slope of the Ratu Boko site. The consequence of building facilities, occurred increasing of deformation either static load or dynamic load around outside foundation. By viewing from slope stability, also occurred the decrease of slope safety factor up to this condition is 1,274 compared with natural slope is 2,767, and olso the increasing displacement different to both outside foundation that is induced space of both columns changed such as existing condition by + 3 cm. the crack of joined beam and column outside such as existing condition (1-2mm) effected by the accumulation of outside vertical foundation displacement more than after the earthquake and excavation foundation so that it induced angular distortion is 1/213. After setting out the supported column it is effective enough to reduce the increasing before, by caused of earthquake load the difference of displacement within both outside column is 1mm, the displacement of inside vertical foundation more than of outside foundation with the result that it reduces angular distortion before becoming 1/148, as well as increasing the safety factor of slope when the earthquake that is 2,489. In terms of angular distortion, due to static load the values obtained still relatively high that is 1/199 if supported column carried out together with building facilities, but this damage including light.numerical approach 2D model with software Plaxis proved to be able to model of soil structure as well as building altogether to obtain their interaction.

Kata Kunci : deformasi lereng, displacement fondasi, angular distortion, faktor aman, metode elemen hingga.