Workreport 2019-7



Correlation of Transmissive Fractures of Pilot Holes ONK-PH4-PH28 and Fracture Traces Mapped from the ONKALO Tunnel


Tammisto, E., Nummela, J.



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Posiva flow logging (PFL DIFF) tool is a device designed to detect and measure the flow rate of transmissive fractures intersecting holes drilled in crystalline rock. PFL DIFF results measured with a 0.5 m test interval and 0.1 m steps along the drillhole can be compared to fractures logged from the optical drillhole wall images and drillcore sample in order to identify the transmissive fractures from the fracture logging results.

In the geological mapping of ONKALO fracture traces are mapped from the ONKALO tunnel walls. The mapping results are digitized to a 3D tunnel layout in Surpac® Vision programme and the fracture properties are collected and saved to POTTI database. Tunnel fractures are classified as flowing, dripping, wet, damp or dry. The water leaking surfaces on the ONKALO tunnel walls are mapped yearly as part of the Olkiluoto monitoring program (OMO) using an equal five step measure as used with the water leaking fracture traces in ONKALO. 

In this work transmissive fractures detected in the PFL DIFF measurements in pilot holes ONK-PH4–ONK-PH28 were correlated with the fractures mapped from the ONKALO tunnel walls. The correlation was carried out by comparing the location and orientation of the transmissive fractures of the pilot holes and the fracture traces of the tunnel wall in a 3D AutoCAD model. Additionally water leakage information of each tunnel fracture trace and water leakage areas of the tunnel wall were considered as a transmissivity indicator.

The main objective of the work was to identify transmissive fractures in ONKALO drillholes and to get a better understanding of the relationship between the transmissive fractures in the pilot holes, tunnel cross cutting fractures (TCF), water leaking tunnel fractures and water leakage areas on the tunnel wall. The purpose was also to identify the tunnel fractures that correspond to the transmissive fractures identified with the PFL DIFF method in the pilot holes.


ONKALO, groundwater, fractures, hydraulically conductive fractures, transmissive fractures, groundwater flow, hydraulic conductivity, correlation, TCF


WR 2019-07_web (pdf) (19.1 MB)


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