Analisis Potensi Likuefaksi Kawasan Strategis Pariwisata Nasional Loh Buaya, Pulau Rinca

Heryawan Kurnia Rakhman, Dr.Eng. Ir. Sito Ismanti, ST., M.Eng., IPM; Prof. Ir. Trias Aditya Kurniawan M., S.T., M.Sc., Ph.D., IPU.

2024 | Tesis | S2 TEKNIK PENGELOLAAN BENCANA ALAM

Guna meningkatkan pertumbuhan wisatawan di Indonesia, pemerintah telah menetapkan dan membangun berbagai infrastruktur penunjang di Kawasan Strategis Pariwisata Nasional (KSPN). Salah satu KSPN yaitu Loh Buaya, Pulau Rinca yang merupakan habitat komodo, telah dibangun berbagai infrastruktur penunjang seperti dermaga, jalan elevated, penginapan dan pusat informasi. Berdasarkan beberapa referensi, Pulau Rinca merupakan daerah rawan terkena bencana gempa bumi. Selain gempa, terdapat bencana lainya yang dapat timbul setelah gempa salah satunya yaitu likuefaksi. Likuefaksi merupakan fenomena hilangnya kekuatan tanah akibat tekanan air pori yang meningkat dipicu oleh adanya gempa. Penelitian ini bertujuan untuk mengetahui potensi gempa, kerentanan likuefaksi dan dampaknya terhadap infrastruktur yang telah terbangun.

Penelitian ini diawali dengan analisis terhadap gempa menggunakan dengan metode Probabilistic Seismic Hazard Analysis (PSHA) dan Deterministic Seismic Hazard Analysis (DSHA). Selanjutnya dilakukan analisis kerawanan likuefaksi menggunakan data gempa yang telah didapatkan dari analisis sebelumnya dan data hasil penyelidikan tanah yang diperoleh dari Kementerian PUPR. Analisis potensi likuefaksi dilakukan dengan berbagai tahapan yaitu analisis awal berdasarkan kedalaman muka air tanah (MAT) dan distribusi butir. Selanjutnya dilakukan analisis lanjutan meliputi analisis menggunakan simplified procedure, Liquefaction Potential Index (LPI), Liquefaction Severity Index (LSI), mikrozonasi LSI dan potensi penurunan tanah akibat likuefaksi. Setelah diketahui bahwa terdapat potensi likuefaksi penelitian dilanjutkan untuk melakukan evaluasi daya dukung fondasi pada bangunan yang telah terbangun.

Hasil yang diperoleh dari penelitian ini yaitu kawasan wisata Loh Buaya Pulau Rinca memiliki potensi diguncang gempa dengan magnitudo 6,8 Mw dengan jarak 70-80 km yang menghasilkan PGA di permukaan tanah sebesar 0,59 g. Gempa tersebut berpotensi mengakibatkan likuefaksi dengan indeks LSI sangat tinggi pada tanah berjenis pasir lepas dengan muka air tanah yang dangkal. Lokasi tersebut berada di bangunan penginapan dan sebagian bangunan pusat informasi. Potensi likuefaksi tersebut juga dapat mengakibatkan penurunan tanah hingga 1,21 m. Namun berdasarkan analisis daya dukung fondasi secara aksial diperoleh bahwa daya dukung fondasi izin bangunan penginapan masih lebih besar dibandingkan beban aksialnya. Hal ini dikarenakan fondasi tiang pancang memiliki kedalaman hingga tanah yang tidak terlikuefaksi sehingga tetap mampu menahan beban aksialnya.

In order to increase the growth of tourists in Indonesia, the Indonesian government has determined and built various supporting infrastructure in the National Tourism Strategic Area (KSPN). One of the KSPNs, Loh Buaya, Rinca Island, which is the habitat of Komodo dragons, has built various supporting infrastructure such as jetties, elevated roads, homestays and information centers. Based on several references, Rinca Island is an area prone to earthquakes. In addition to earthquakes, there are other disasters that can arise after an earthquake, one of which is liquefaction. Liquefaction is a phenomenon of loss of soil strength due to increased pore water pressure triggered by an earthquake. This study aims to determine the earthquake potential, liquefaction vulnerability and its impact on infrastructure that has been built.

This research begins with earthquake analysis using the Probabilistic Seismic Hazard Analysis (PSHA) and Deterministic Seismic Hazard Analysis (DSHA) methods. Furthermore, the analysis of liquefaction vulnerability was carried out using earthquake data that had been obtained from previous analyses and soil investigation data collected from the Ministry of Public Works and Housing. Analysis of liquefaction potential was carried out in various stages, namely initial analysis based on the depth of the groundwater table and grain size distribution. Further analysis was carried out including analysis using the simplified procedure, Liquefaction Potential Index (LPI), Liquefaction Severity Index (LSI), LSI microzonation and settlement due to liquefaction. After realizing that there is a potential for liquefaction, the research continued to evaluate the bearing capacity of the foundations of the buildings that have been built.

The results obtained from this study are that Loh Buaya tourist area, Rinca Island has the potential to be shocked by an earthquake with a magnitude of 6.8 Mw with 70-80 km which results in a PGA at the ground surface of 0.59 g. The earthquake has the potential to cause liquefaction with a very high LSI on loose sandy soils with a shallow groundwater table. These are located in the guesthouse and some of the information center buildings. The liquefaction potential can also result in ground settlement of up to 1.21 m. However, based on the axial bearing capacity analysis of the foundation, it is found that the allowable bearing capacity of the guesthouse foundation is still greater than the axial load. This is because the end bearing of the pile depth until not liquefiable soil so that it is still able to hold the axial load.

Kata Kunci : daya dukung fondasi, likuefaksi, mikrozonasi, penurunan tanah, percepatan tanah puncak