Geotechnical properties in relation to grain-size and mineral composition: case study landslide in the Rječina Valley (Croatia)

Abstract

Investigated landslide is the largest active mass movement along the Croatian coast, situated on the north-eastern slope in the central part of the Rječina Valley (north-eastern coastal part of Adriatic Sea, Croatia). Slopes in this valley are formed in siliciclastic rocks - flysch, while limestone rock mass is visible on the cliffs around the top of the river valley. The slopes are at the limit of a stable equilibrium state, and mass movement phenomena have been recorded since 19^th century.

Samples for laboratory testing were taken from the flysch bedrock, weathered zone and slope formations, and were recovered to provide specimens for data on their mineralogical, physical and geotechnical properties. Correlation between mineralogical and geotechnical properties and their influence on sliding processes are presented in this paper. Clay fraction in samples ranges from 17 % to 38 %. Clay activity of the tested samples is from 0.45 to 0.89, and the residual friction angle varies from 13.0° to 17.7°. These results correspond to the presence of kaolinite and illite groups of clay mineral. Mineral composition and decrease in strength of fine-grained soil materials, due to the increase of pore water pressures, contributes to the slope movements.