Verification of Engineering-Geological/Geotechnical Correlation Column and Reference Level of Correlation (RNK) Method by Observations in the Slip-Plane Zone

The engineering-geological/geotechnical correlation column can be established in zones of limited extent using one or several charac- teristic layers, one of which is selected as the reference layer. The Reference Level of Correlation method, i.e. the RNK (Referentni nivo korelacije in Croatian) method, is a confirmed procedure enabling the establishment of such columns. In the engineering geological/ geotechnical correlation column, the plasticity index is the most significant indicator of the peak friction angle, full-softening friction angle and residual friction angle for coherent soils and soft rock for- mations. As a rule, maximum plasticity index values correspond to the minimum values of such friction angles. This opens up the possibility of an exact engineering-geological/geotechnical model, with accurate differentiation of minimum shear strength zones, zones of different permeability, and zones of various degrees of natural compaction. This procedure was applied inter alia on the successfully improved Granice landslide located in the Zagreb area, where it was proven that elements for verification based on the RNK-method exist for all three areas of investigation: sliding body - drain trench section - detail in the central portion of the sliding zone. The procedure is recommended as a means for finding solutions to similar problems.