During the construction of the Adriatic Highway section near Rijeka, Croatia, a landslide occurred on the slope alongside a highway cut. The affected section of the highway route lies on a flysch slope, in a flysch synclinal valley narrowed by limestone rock mass from the Cretaceous Period. Through lateral expansion, the landslide also affected the partly finished highway cut. The landslide occurred on the site formed in layers of Paleogene flysch, a very complex geological material. Complex geotechnical investigation works were carried out for drafting a landslide remediation project. Based on the results of additional investigation works, a landslide remediation project and a new highway cut construction project were made. The basic rock reinforced structure was replaced by an anchored boring pile-wall structure in the toe of the landslide body. The landslide remediation was based on observational methods. The observational methods show the behavior of designed geotechnical structures and allow for potential corrections. This is especially useful in complex geological conditions where site investigation works are not enough to determine the condition of all site features