Geological hazard controlled by genetic characteristics of material, case study on Bojongkoneng mass movements, Bandung, West Java, Indonesia

Bojongkoneng is a regional area that developed significantly in the recent years. The genetic characteristics of study area is deformed by Quaternary volcanic deposits. Research area is included in the zones of Undifferentiated Young Volcanic Products of Mount Tangkubanparahu. The condition and physical characteristic of materials are important to be considered and useful for regional development. Volcanic rocks are widespread in different geological contexts and exhibit complex behaviors, from hard to extremely soft rocks, depending on mineralogy, porosity, and weathering. In particular, their mechanical properties are influenced by the size and shape of pores. The research objective is to obtain conclusions about the characteristics of volcanic materials that determine the stability of the region, so it can be anticipate the risk of natural disasters especially mass movements. This study result will become the consideration in supporting the plan and activity of development for obtaining the area of natural disaster risk information. The research will be identifying about physical and mechanical properties of surficial soils and rocks by describing their outcrops in study area from which the samples were taken. The volcanic materials have been characterized from field survey, bibliographical references and expertise judgement. Geotechnical properties are similar in both types of soils: in the residual soils, clay – silty fraction is predominant, and in the transported soils silt-clayey fraction predominates. Grain size analysis can be affected by particle aggregation, showing larger size fractions that corresponding with the soil particle size distribution. The main characteristics, according to Casagrande chart, are: most of the residual soils present high plasticity, residual soils as a product of ash alteration, residual soils as a product of tuff alteration.