This paper will analyse the optimal number of required data within geotechnical investigation works with the cost estimation of performed tests and the duration of the testing (line closure). Deviation of the geotechnical parameters obtained from various research works will be shown. Special attention will be paid to the review of the quality of non-destructive methods that require a minimum of line closures. In the paper a case study of extensive geotechnical, geophysical and laboratory investigation works will be presented at the location before and after the Buna Railway Bridge (railway line M104 Novska – Sisak – Zagreb) as part of an international research project SMART RAIL. Conducted investigation works consisted of: engineering geological mapping of the location, exploratory drilling with continuous coring, performance of standard penetration testing in boreholes, field vane testing in boreholes, excavation of trial pits, testing with nuclear densimeter, cone penetration testing with pore pressure measurement (CPTU), testing with flat dilatometer (DTM) and geophysical testing methods; geoelectric tomography, seismic refraction, MASW/REMI, downhole and crosshole seismic survey and ground penetrating radar (GPR). The works are made with the aim of defining the physical and mechanical properties of the existing geotechnical structures (embankment) and foundation soil (primarily the stiffness of individual embankment layers), and general geotechnical conditions at the site. This is essential for the assessment and valorisation of any potential geotechnical problem that arise
in the transition zones, and finally to create the reliable geotechnical models and to design the reconstruction of the new transition zone between the bridge abutments and geotechnical
structures (embankment).

transition zones; geotechnical investigation works