Determination of Crucial Shear Parameters in Highly Landslide Prone Tropical Soils in Bello Oriente, Medellín, Colombia

The project Inform@Risk is developing a low-cost landslide early warning system in the barrio Bello Oriente in Medellín, Colombia. Especially the block-in-matrix structure of the deeply fractured dunite rock, created by weathering and former landslide events, in the area is prone to landslides. Therefore, the geological investigation of the subsurface material focuses on the shear parameters of the matrix since the blocks do not contribute to dynamic and behaviour of the landslides considerably. During the test installation of the Early Warning Systemin the barrio in September/October 2021 some samples for direct shear tests have been collected in the trenches for the TDR lines and tested in the laboratory of Integral S.A.S in Medellín. The friction angle shows minor differences between the samples, the cohesion, however, provides evidence of major variation. The difference is created by a combination of varying grain size distribution, water content and density. Since the determined friction angle of the material and the slope angle of the study site are congruent, the slope is suggested to be in an instable equilibrium and might fail after heavy rainfall or other additional water input. The early warning system is, therefore, of high importance to the well-being of the inhabitants.