THE KOSTANJEK LANDSLIDE IN ZAGREB

The large landslide, Kostanjek, on the southern slopes of the mountain , Zagrebacka Gora, in the western suburb of Zagreb was activated in 19 63 after some 2.1 x 10(6) m(3) of marl for the cement factory, Croatia , was excavated at the foot of the slope. The geological features (sin clinal structure, faults, hydrogeological conditions, extension of the ''Tripoli'' marl strata) which had an important role in the formation of the slide, as well as the means of marl exploitation by means of m ass blasting, are presented in the paper. The Kostanjek slide involves an urbanized area of some 100 ha. It is estimated that a sliding mass of some 32 x 10(6) m(3) is involved, with a maximum depth of 90 m. Sl iding occurs in three levels. The displacements of the surface are 3-6 m. The excavation of marl was stopped in 1988, when a total of 5.3 x 10(6) m(3) of material was excavated. Since then the magnitude of surf ace displacement per year has decreased. The Kostanjek slide is still active. It is estimated that natural stabilization will take a long ti me, probably decades. Analyses of possible measures for the stabilizat ion of movements suggested that preventive drainage with continuous ob servation of the slide is most suitable.