EVALUATION OF LIQUEFACTION POTENTIAL ASSOCIATED WITH LAND SUBSIDANCE AND LATERAL DISPLACEMENT IN HUMENE, GUNUNGSITOLI IDANOI DISTRICT, GUNUNGSITOLI REGENCY NIAS ISLAND

• Main Author: Recxy Vegantara, Aldy
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/81710
• Institution: Institut Teknologi Bandung

The village of Humene, located in Gunungsitoli Idanoi District, Gunungsitoli Regency, Nias, is dominated by Quaternary deposits consisting of clay deposits, clayey sand, silty sand, and sand. This region and Nias Island are part of the forearc of Sumatra Island, which is included in the Sunda subduction system, making it susceptible to liquefaction due to its proximity to the subduction zone. This study was conducted in Humene Village to determine the characteristics of Quaternary deposit materials, the potential for liquefaction, ground settlement due to liquefaction, and lateral displacement. The methods used were based on observations from two boreholes and twelve cone penetration test (CPT) graphs, as well as laboratory tests on borehole samples, including soil specific gravity, grain size distribution, and soil plasticity. The potential impact of earthquakes on the study area was simulated using the Indonesian Earthquake Source and Hazard Map 2017 SNI (987-602-5489-01-3), applying the Robertson, Boulanger, and Idriss equations, with an earthquake magnitude of 7,5 Mw as the standard and 8,1 Mw as the largest recorded earthquake in the study area. The safety factor (fs) values reflect the liquefaction potential and its relationship to ground settlement and lateral displacement. Based on in situ observations, including borehole cores, CPT graphs, and laboratory analyses, the soil characteristics in the study area are divided into three depositional environments: fluvial, beach ridge, and small-scale marine. Generally, the silty sand material in the study area has high liquefaction potential. This material, characteristic of the fluvial environment, is predominantly found at depths of 2-10 meters, with NSPT values ranging from 4- 24 and cone resistance less than 100 kg/cm². The liquefaction potential index values from the earthquake acceleration simulation and using two equations all fall into the high liquefaction potential category, while the LSI values from the earthquake acceleration simulation show more varied results, ranging from low to very high liquefaction potential. In terms of ground settlement and lateral displacement, the study area is categorized as having severe damage potential due to liquefaction. The ground settlement values from the Robertson, Boulanger, and Idriss equation simulations for a standard magnitude of 7,5 Mw range from 23,3 cm to 54,04 cm and 32,48 cm to 54,06 cm, respectively. For a magnitude of 8,1 Mw, the values range from 40,02 cm to 66,36 cm and 42,12 cm to 66,36 cm, respectively. The Robertson equation showed better correlation when fs values were compared to ground settlement values, with R² values of 0,8436 and R values of 0,9272 for the standard magnitude, and R² values of 0,8553 and R values of 0,91274 for a magnitude of 8,1 Mw. In contrast, the Boulanger and Idriss equation yielded R² values of 0,6288 and R values of 0,7280 for the standard magnitude, and R² values of 0,6191 and R values of 0,7131 for a magnitude of 8,1 Mw. Therefore, the Robertson equation is more optimally applied at the study site for CPT testing.