Reinforced concrete shafts for the structural mitigation of large deep-seated landslides: an experience from the Macesnik and the Slano blato landslides (Slovenia)

During the last decade, several rainfall-induced deep-seated large landslides with volumes of the order of 1 million m3 were triggered in various locations in Slovenia (central Europe), each representing a serious threat to the nearby villages and traffic infrastructure and urging to be mitigated. The Macesnik landslide, triggered in 1989, and the Slano blato landslide, triggered in 2000, were the first two large landslides in Slovenia, where a combination of drainage and retaining works consisting of deep reinforced concrete (RC) shafts/wells was successfully used as a mitigation measure. This paper presents the field conditions and a brief history of the two landslides with emphasis on the design approach and method used for the stability analysis and the design of deep RC shafts/wells. In addition, the paper gives an insight into the problems associated with the execution of works and provides data about the behavior of the two landslides after drainage and retaining works were completed. The monitoring data show that the undertaken mitigation measures were efficient to improve the stability of both landslides and significantly reduce the risk.