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