Landslide affected with an open pit excavation

In autumn 1999, during the excavation of an open pit for the sport hall of Nautical High School in Bakar, Croatia, the instability of pit wall was occurred and a landslide in the slope above the pit was formed. The wider environment of the site is formed in flysch rock mass and lies in a flysch synclinal valley narrowed by limestone rock mass. Flysch rock mass mainly consists of laminated silt to silty shale, sandstones, and interbeds of conglomerate and limestone. The flysch complex bedrock is characterized by huge lithological heterogeneity and it is almost completely covered by clayey weathering zone material and slope deposits. The landslide body was formed during the open pit excavation, in the clayey cover with slope surface formed on the contact of the cover and the bedrock due to the high ground water level in the slope. After landslide occurring, the complex geotechnical investigation works were conducted. Based on their results and observational method, a landslide remediation measures and an open pit construction were designed. The aim of the first phase of the landslide remediation was to stop further displacements of the landslide body and drop the ground water level in the slope. These measures were carried out by filling of landslide toe with crushed stone material and trenching of excavated drains in the lower part of landslide body. In this paper we will describe the history of the landslide occurrence, geotechnical properties of the landslide and proposed remediation.