International Journal of Advanced Science and Technology Vol. 29, No. 7, (2020), pp. 3166-3173 3166 ISSN: 2005-4238 IJAST Copyright ⓒ 2020 SERSC Geotechnical Characteristics of Volcanic Red Clay Soil Related to Geoengineering Problem in Sekincau, Sumatra, Indonesia Prahara Iqbal 1,2* , Dicky Muslim 3 , Zufialdi Zakaria 4 , Haryadi Permana 5 , Arifan Jaya Syahbana 6 , Yunarto 7 , Jakah 8 1,3,4 Geological Engineering Faculty, Padjadjaran University, Jatinangor, Sumedang, 45363, Indonesia 2,5,6,7,8 Research Center for Geotechnology, Indonesian Institute of Sciences, Cisitu, Bandung, 40135, Indonesia Abstract The study of physical, mechanical, and mineralogy characterization of volcanic red clay soil in the Sekincau Sub-District, West Lampung, Indonesia to obtain the genetic and soil engineering characterization related to the geoengineering problem. The method of this study is the Geotechnical laboratory method, XRD, and SEM method. The results of the analysis show that the volcanic red clay soil in the study area is residual soil produced from the weathering of volcanic rocks composed of felsic minerals in tropical environments. This soil is clayey silt (MH), loose, easily eroded, has the specific gravity 2.52 - 2.90, water content 27.21% - 67.14%, water saturation 72.98% - 94.75%, porosity 54.43% - 67.00%, the liquid limit value of 52.54- 121.17%, a plasticity index value of 17.82-35.17%, permeability 7.4E-08 - 7.22E-05, has cohesion less than 1 Mpa, and an internal friction less than < 30 o . Quartz, halloysite, kaolinite, and montmorillonite are the clay minerals that can be found in this soil. It can be concluded that volcanic red clay soil in the study area is easy to landslide during the rainy season. Keywords: geoengineering problem, residual soil, Sekincau, Sumatra, soil engineering characterization, volcanic soil. 1. Introduction Red clay soil is the reddish color dominant clay, composed of various types of clay minerals, and it is residual soil [1], [2]. This soil is a direct product of physical and chemical bedrock weathering [3]. Based on the degree of weathering of rocks, this soil is located or equivalent to zone VI [1], [4], [5], [6] revealed that the soil has complex and diverse properties. In Indonesia, red clay soil can be found in the quaternary geological environment of volcanic rock (volcanic red clay soil), occupying 53% of land area, and it is used for various types of infrastructure establishment [7]. Various types of problems (geoengineering problem) often occur in the infrastructure that stands on this type of soil, such as landslides [8], [9], 10]. Previous studies related to volcanic red clay soil in Indonesia have been carried out. The study described the engineering characteristics of volcanic red clay from various rock formations on Java [11], [12], Sumatra [13], [14] and Kalimantan/Borneo [15], Indonesia. However, the studies carried out have not yet described how the characteristics of volcanic red clay soil engineering in a comprehensive way (geology, Geotechnics, and geochemistry). Therefore, the authors conducted research and studies on the engineering characteristics of volcanic red clay soil in terms of geology, Geotechnics, and geochemistry to reveal its engineering characteristics related to geoengineering problem. The novelty of this research is to reveal the tropical volcanic red clay soil characteristics from the genetic, physical and mechanical properties, and clay mineral content. 2. Geologic setting West Lampung area is in the tropical climate. Based on the tropical climate classification included in the tropical wet type. This area has an average temperature of 24.5 o with an average humidity level of 86%. Based on the type of rainfall zone map [16] this area is in the equatorial rainfall zone, which is the area that gets the most rainfall from September to April. The average rainfall in West Lampung is 2000-3000 mm per year [17].