The Analysis of Liquefaction Potential and Designing Its Countermeasure by Applying Stone Column Method

FAHRIZAL PATRIAMAN, Prof. Ir. T. Faisal Fathani, S.T., M.T., Ph.D., IPU., ASEAN. Eng; Dr. Wahyu Wilopo, S.T., M. Eng

2022 | Tesis | MAGISTER TEKNIK PENGELOLAAN BENCANA ALAM

Pulau Sulawesi memiliki Sesar Palu Koro yang aktif bergerak dengan magnitudo perpindahan tinggi tetapi kegempaan rendah. Pada tanggal 28 September 2018, pukul 18:02 waktu setempat, terjadi gempa bumi di Sesar Geser Palu Koro. Investigasi lapangan di sepanjang Pantai Palu mengungkapkan likuefaksi terjadi di daratan dan di pesisir pantai. Daerah penelitian terletak di kawasan pesisir Teluk Palu, Provinsi Sulawesi Tengah. Penelitian ini dilakukan untuk mengetahui potensi dan mitigasi likuefaksi di kawasan Teluk Palu. Data yang digunakan berupa Standard Penetration Test dan analisis potensi likuefaksi dilakukan dengan metode simplified procedure. Selanjutnya untuk mengetahui tingkat potensi likuefaksi diterapkan Liquefaction Potential Index. Upaya mitigasi bahaya likuefaksi menggunakan metode stone column yang menerapkan metode perhitungan Priebe. Perangkat lunak QGIS diterapkan untuk memetakan hasil analisa. Pengamatan geologis menunjukkan bahwa kondisi tanah di kawasan Teluk Palu didominasi oleh tanah non-kohesif (pasir). Berdasarkan analisis potensi likuefaksi, sebagian besar wilayah timur Teluk Palu tidak menunjukkan potensi likuefaksi. Sebaliknya, bagian barat dan selatan terindikasi memiliki potensi likuefaksi. Hasil analisis Liquefaction Potential Index menunjukkan bahwa wilayah barat dan selatan didominasi dengan potensi likuefaksi yang sangat tinggi. Sementara di wilayah timur sangat rendah. Potensi likuefaksi yang rendah dicapai melalui perbaikan tanah berdasarkan kriteria yang ditentukan. Hasil pemetaan menunjukkan kebutuhan desain stone column dengan jarak spasi yang lebih dalam dan dekat di wilayah barat dan selatan dibandingkan dengan di wilayah timur. Karena banyaknya variasi desain stone column yang dihasilkan dari analisis mitigasi, maka dilakukan penyederhanaan untuk memudahkan pelaksanaan konstruksi.

Sulawesi Island has a Palu Koro Fault that actively moves with a high displacement magnitude but low seismicity. On 28 September 2018, at 18:02 local time, an earthquake occurred in Palu Koro Shear Fault. The field investigations along the Palu coast revealed new evidence regarding the extensive liquefaction in these areas, both inland and coastal land. This research's location is the Palu Bay coastal area, Central Sulawesi Province. Moreover, this research was conducted to determine the potential and mitigation liquefaction in the Palu Bay area. The data used was in the form of the Standard Penetration Test of the area, and the simplified procedure method was carried out to analyze the potential liquefaction. Furthermore, to determine the level of liquefaction potential, Liquefaction Potential Index was applied. Mitigation effort on the liquefaction hazards comprised a stone column method that applied Priebe's calculation method. QGIS software was applied to map the results. Geological observations showed that non-cohesive soil (sand) dominates the soil condition in the Palu Bay area. Based on the potential liquefaction analysis, most of the eastern region of the Palu Bay area showed no liquefaction potential. On the contrary, the western and southern parts were indicated to have liquefaction potentials. The Liquefaction Potential Index analysis results showed extremely high liquefaction potentials dominate the western and southern areas. Meanwhile, in the eastern area, it was extremely low. Low liquefaction potential was achieved through soil improvement based on the specified criteria. The mapping result indicated the design for stone columns with deeper and closer spacing distance on the western and southern areas than those in the eastern areas. Due to the wide variety of stone column designs resulting from the mitigation analysis, simplification was made to facilitate the construction implementation.

Kata Kunci : liquefaction, simplified procedure, potential liquefaction index, Priebe method, stone column, coastal area