Correlation of transmissive fractures in pilot holes ONK-PH8 - PH12 and fracture traces mapped in ONKALO

In a preceding study Posiva flow logging (PFL) with a 0.5 m test interval and 0.1 m steps has been used together with optical drillhole images and core logging fracture data for the exact determination of the depth of hydraulically conductive fractures in pilot holes. The fracture traces have been mapped from the ONKALO tunnel walls as a part of the systematic mapping. The mapping results has been digitized to a 3D tunnel layout in Surpac programme. The data integrity and fracture trace uniqueness has been verified by Datactica Oy and further collected to a database (RakokantaDatacticaPosiva20100607.mdb). Fractures mapped with leakage attribute have been defined as flowing, dripping, wet, or damp where the attribute is recorded. The fractures with no leakage attribute value appear to be non leaking. The water leaking surfaces on the ONKALO tunnel walls have been mapped sequentially and conclusively (once or twice a year) as a part of the Olkiluoto monitoring program (OMO) using an equal five step measure as used with fracture traces in systematic mapping. The PFL results correlated with core logging fracture data from the pilot holes ONK-PH8 - ONK-PH12 were in this work further correlated with the fractures mapped from the ONKALO tunnel walls. Each hydraulically conductive fracture of ONK-PH8 - ONK-PH12 was investigated and linked to ONKALO fracture of a coherent orientation and matching location, where such fracture trace was available. Also tunnel crosscutting fracture (TCF) data was used in combining, since the systematic mapping data was not yet available for the pilot holes ONK-PH11 and ONK-PH12 at the time of the evaluation. The main objective of the work was to identify the ONKALO fractures which correspond to the flow from fracture(s) identified with the PFL method in pilot holes and to collect basic information about the occurrence, frequency and orientation of water bearing fractures along the ONKALO tunnel. The correlated hydraulically conductive fractures from the pilot holes ONK-PH8 - ONK-PH12 were imported as circle polygon objects to a 3D AutoCAD model. The mapped and verified 13 247 ONKALO fracture traces were divided to 3 subsets according to their length: (6 fracture traces in FDB (Fracture Database) were lacking the length attribute) 433 long fractures (length equal or greater than 10 m), 1 288 medium length fractures (length less than 10 m but equal or greater than 3.5 m) and 11 520 short fracture traces (length less than 3.5 m) and then imported to 3D model to be linked to hydraulically conductive fractures of pilot holes. The combining was carried out by investigating the location and orientation of each suspected pair of a polygon (PFL fracture) and a polyline in the 3D AutoCAD model. Additionally leakage attribute of each ONKALO fracture trace was considered as an conductivity indicator and the fracture traces bearing leakage classification were combined with the PFL fractures. (orig.)