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 beestablished in zones of limited extent using one or several characteristiclayers, one of which is selected as the reference layer. TheReference Level of Correlation method, i.e. the RNK (Referentni nivokorelacije in Croatian) method, is a confirmed procedure enablingthe establishment of such columns. In the engineering geological/geotechnical correlation column, the plasticity index is the mostsignificant indicator of the peak friction angle, full-softening frictionangle and residual friction angle for coherent soils and soft rock formations.As a rule, maximum plasticity index values correspond to theminimum values of such friction angles. This opens up the possibilityof an exact engineering-geological/geotechnical model, with accuratedifferentiation of minimum shear strength zones, zones of differentpermeability, and zones of various degrees of natural compaction.This procedure was applied inter alia on the successfully improvedGranice landslide located in the Zagreb area, where it was proven thatelements for verification based on the RNK-method exist for all threeareas of investigation: sliding body – drain trench section – detail inthe central portion of the sliding zone. The procedure is recommendedas a means for finding solutions to similar problems.