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Subsurface Mapping and Geotechnical Design for Landslide Mitigation Hasan, Muhammad Fathur Rouf; Susilo, Adi; Sutan Haji, Alexander T.; Suryo, Eko Andi; Agung, P. A. Maha; Idmi, Mohammad Habibiy; Musta, Baba
Civil Engineering Journal Vol. 11 No. 9 (2025): September
Publisher : Salehan Institute of Higher Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.28991/CEJ-2025-011-09-015

Abstract

The landslide near the PT Molindo Incinerator Unit poses a significant threat to the facility’s structural integrity. Without immediate mitigation measures, the incinerator building is at risk of collapse, potentially impacting adjacent settlements due to cascading structural failures. To reduce the risk of further instability, urgent geophysical investigation is required to characterize the subsurface lithology and assess the groundwater table conditions. A geoelectrical resistivity survey was conducted using the Schlumberger configuration across 8 measurement points along a 100-meter survey line, with 10-meter electrode spacing. The resistivity measurements ranged from 3.30 to 25 Ωm, which were interpreted as clay-rich layers; 26 to 167 Ωm, corresponding to sandy clay; and 167 to 15,944 Ωm, indicating bedrock. The potential slip zone is interpreted at an average depth of 20 to 25 meters, indicated by very low resistivity values with resistivity values between 3.30 and 25 Ωm. Field observations confirmed that the landslide materials predominantly consisted of clay soils, distributed within two distinct layers beneath the incinerator unit. The combined depth of the clay and overlying sandy layers was estimated to reach approximately 20-25 meters from the ground surface. To ensure the effectiveness of structural mitigation, a retaining wall must be designed to extend beyond this depth threshold. Numerical simulations using Slope/W software indicated that soil nailing techniques yielded safety factors ranging from 1.32 to 1.81 under static conditions and 1.22 to 1.43 under dynamic conditions. Predicted deformations ranged from 0.01 to 0.02 meters (static) and 0.02 to 0.03 meters (dynamic). These results suggest that soil nailing is a viable reinforcement method to stabilize slope movements, particularly during periods of high rainfall. Additional recommended mitigation strategies include the installation of surface and subsurface drainage systems to control water flow, constructing retaining structures to serve as physical barriers to soil movement, and using vegetative cover to enhance slope stability.
Micron to Nano Au Particles Incorporation in Different Stages of Pyrite, in Bau, Sarawak, Malaysia Sundarrajan, Vijay Anand; Marjon, Carolin Nicole; Musta, Baba
Indonesian Journal on Geoscience Vol. 12 No. 1 (2025)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.12.1.89-103

Abstract

In eastern Malaysia, Bau is the significant sediment hosted gold deposit (SHG), and Sarawak Province was the main gold (Au) producer in East Malaysia. The annual production rate was approximately 40 ̶ 50 metric tons of Au (high grade). The Bau mining is located 40 km SW of Kuching City, Sarawak. For the present study, around twenty-five samples were collected in the Au mineralized zones of Bau areas. The polished thin sections were prepared for mineral chemistry and fluid petrography analyses. The samples were studied through transmission microscope, Electron Probe Micro-Analyzer (EPMA), and fluid inclusion studies. From ore petrography, four stages of pyrite were classified. The first generation of pyrite is the early stage of diagenetic pyrite (Py1), Py2 is subeuhedral pyrite, Py3 is zoned pyrite, and Py4 is post-diagenetic pyrite. The mineral chemistry of different stages of pyrite was measured through EPMA. However, it is worth noting that the concentrations of these trace elements in pyrite have decreased pre-diagenetic and post diagenetic stages. The precipitation of Au in the main stages of pyrite was mainly controlled by pyrite structure, fluid ligands, and the temperature of crystallization.