[en] The construction of ONKALO access tunnel started in September 2004 at Olkiluoto. During the construction, investigations serving both research and construction purposes need to be done. Investigations can be done for example in so called pilot holes. Pilot holes are cored drillholes to be drilled to the tunnel profile. The length of the holes varies from some tens of meters to some hundreds of meters. The purpose of the holes is to confirm the quality of the rock mass for tunnel construction, especially to identify water conductive fractures/fracture zones and provide information that could result in modifications of the existing construction plans. The pilot hole ONK-KR13 was drilled in March 2010. Drilling was started from chainage 4201. The final length of the hole was 140.05 meters. The deviation of the drillhole was measured during and after the drilling. Additionally, oriented core samples were collected and electric conductivity of returning water from the drill hole was measured. Logging of the core samples included following parameters: lithology, foliation, fracturing, fracture frequency, RQD, fractured zones, core loss and weathering. The rock mechanical logging was based on Q-classification. The strength and deformation properties of the rock were defined by using Rock-Tester equipment. Hydraulic measurements were made by using the PFL DIFF (Posiva Flow Log, Difference Flow method). PFL DIFF measurements were performed with a 0.5 m section length and with 0.1 m length increments. With PFL DIFF tool the locations of flowing fractures and their transmissivities were detected. Simultaneously, the electric conductivity (EC) of the drillhole water and fracture-specific water, temperature of the drillhole water, single point resistance (SPR) of the drillhole wall and the prevailing water pressure profile were measured. Water loss measurements were done after the drilling by the tool developed by Posiva. The equipment was in test use during the measurements. Groundwater samples were not collected due to too low inflow to the drillhole. Geophysical surveys included natural gamma radiation, gamma-gamma density, magnetic susceptibility, Wenner resistivity, short and long normal resistivity, single point resistance, drillhole radar and full waveform sonic measurements as well as optical and acoustic imaging. The results were joined with the available geological data received from Posiva. A group of geoscientists produced an integrated interpretation based on the investigation results of ONK-PH13. In single-hole interpretation the objective is to identify and describe the general characteristics of major rock units and possible deformation zones within a drillhole. A single-hole interpretation involves integrated interpretation of the data from the geological mapping, geophysical logging as well as hydrogeological investigations. The method is regarded useful for integrated and detailed modelling for the use of the RSC (Rock Suitability Criteria) program. (orig.)