Liquefaction Potential Analysis Using Empirical, Numerical Approach And Its Mitigation Plans In The Maranatha Area, Sigi Regency

Muhammad Ikhsan, Prof. Dr es.sc tech Ir. Ahmad Rifai, M.T., IPM

2024 | Tesis | S2 TEKNIK PENGELOLAAN BENCANA ALAM

Fenomena Likuifaksi yang terjadi di Sulawesi Tengah pada bulan September 2018 dipicu oleh gempa bumi dahsyat yang menimbulkan kerusakan luas dan korban jiwa. Karena letaknya yang dekat dengan sesar teraktif di Sulawesi Tengah, Sesar Palu Koro, maka masih besar kemungkinan terjadinya likuifaksi ulang di dekat kawasan tersebut.
Penelitian ini bertujuan untuk mengetahui dampak likuifaksi di sekitar pembangunan jembatan transmisi air baku Pasigala di Kabupaten Sigi jika terjadi gempa serupa dengan kejadian gempa di tahun 2018. Beberapa data geoteknik yang digunakan dalam penelitian ini seperti stratigrafi, SPT, tinggi muka airtanah, dan data seismik. Pendekatan empiris menggunakan Simplified Procedure yang dikemukakan oleh Idriss dan Boulanger (2014) sedangkan pendekatan numerik menggunakan modul Geostudio Quake/w dan MIDAS GT NX.
Dari interpretasi data geoteknik diketahui bahwa sebagian besar lapisan di sekitar Transmisi Air Baku Pasigala, khususnya Ruas Maranatha, merupakan jenis tanah berpasir. Muka air tanah terletak antara -2,1 dan -11 m di bawah permukaan tanah. Diketahui, lubang bor-37 memiliki muka airtanah (MAT) paling dangkal yaitu mencapai kedalaman -2 m dari permukaan tanah berdasarkan data plotting muka airtanah. Di antara 8 lubang bor yang diteliti, 3 diantaranya rawan likuifaksi pada kedalaman dan ketebalan lapisan tertentu dengan simulasi menggunakan daya 7,5 Mw. Lubang bor-37 diketahui paling rentan terhadap likuifaksi menurut Pendekatan Empiris dan Numerik. Nilai LPI menunjukkan tingkat potensi likuifaksi pada wilayah yang diteliti dengan tingkat potensi sangat rendah hingga sangat tinggi. Hasil penelitian menunjukkan bahwa nilai LPI tertinggi berada pada BH-37. Model numerik menunjukkan bahwa ada kemungkinan terjadinya likuifaksi aliran di Ruas Maranatha jika terjadi gempa berkekuatan 7,3 Mw di wilayah tersebut. Karena adanya potensi likuifaksi, maka perlu diterapkan mitigasi di dekat lokasi, dimana pada penelitian ini rencana mitigasi yang dipilih adalah Penggantian Tanah Timbunan Granular dan Kolom Batu.

The Liquefaction phenomenon that occurred in Central Sulawesi in September 2018 was triggered by a powerful earthquake that caused extensive destruction and loss of life. Due to its location close to the most active fault in Central Sulawesi, Palu Koro fault, there is still a high probability of re-liquefaction occurrence near the area.
This research aims to find the liquefaction effect near the pasigala raw water bridge transmission construction in Sigi Regency if a similar earthquake occurred. Some geotechnical data were carried out in this research such as stratigraphy, SPT, groundwater level, and seismic data. The empirical approach was using the Simplified Procedure by Idriss and Boulanger (2014) while numerical approaches were using the Geostudio module Quake/w and MIDAS GT NX.
The geotechnical data interpretation, reveals that the majority of the layers near Pasigala Raw Water Transmission, particularly the Maranatha Section, are sandy soil types. The groundwater table lies between -2.1 and -11 m below the soil surface. It is known that borehole-37 has the shallowest groundwater table (MAT), reaching a depth of -2 m from the ground surface, based on the groundwater table plotting data. By simulating at a specific depth and layer thickness, three of the eight examined boreholes are susceptible to liquefaction (earthquake of 7.5 Mw). The Empirical and Numerical Approach determined that borehole-37 exhibited the highest susceptibility to liquefaction. With values ranging from extremely low to extremely high, the LPI value shows the liquefaction potential in the area under study. Based on the findings, BH-37 exhibits the highest LPI value. Flow-liquefaction may have concurrently transpired at the Maranatha Section if the 7.3 Mw earthquake struck the region, according to the numerical model. Due to liquefaction potential, mitigations were required to be applied near the site, in this study the mitigation plans chosen are Soil Replacement of Granular fills and Stone Columns.

Kata Kunci : Liquefaction, Numerical Approach, Liquefaction Potential Index.