Workreport 2010-9

Drilling and the Associated Drillhole Measurements of the Pilot Hole ONK-PH9

Karttunen, P. ed., Kosunen, P., Lamminmäki, T., Pekkanen, J., Pöllänen, J., Tarvainen, A-M. & Toropainen, V.

English

194

The construction of the ONKALO access tunnel started in September 2004 at Olkiluoto. Most of the investigations related to the construction of the access tunnel aim to ensure successful excavations, reinforcement and sealing. Pilot holes are drillholes, which are core drilled along the tunnel profile. The length of the pilot holes typically varies from several tens of metres to a couple of hundred metres. The pilot holes are aimed to confirm the quality of the rock mass for tunnel construction, and in particular to identify water conductive fractured zones and to provide information that could result in modifications of the existing construction plans.

The pilot hole ONK-PH9 was drilled from chainage 3263 to chainage 3413.27 in November 2008. The length of the hole is 150.3 metres. The aim during the drilling work was to orient core samples as much as possible. The deviation of the drillhole was measured during and after the drilling phase. Electric conductivity was measured from the collected returning water samples.

Hydraulic conductivity of the fractures or fractured zones was measured by Posiva Flow Log equipment. The measurements were done in two phases. During flow measurements also electric conductivity, grounding resistance and temperature were measured. In flow logging test sections of 0.5 m and increments of 0.1 m were used. The water loss measurements were performed after drilling was completed by the drilling company.

Logging of the core samples included the following parameters: lithology, foliation, fracturing, fracture frequency, RQD, fractured zones, core loss, and weathering. The rock mechanical logging was based on Q-classification. The rock strength and deformation were determined with Rock Tester equipment.

Geophysical logging and optical imaging of the pilot hole included the fieldwork of all surveys, the integration of the data as well as interpretation of the acoustic and drillhole radar data.

One of the objectives of the geochemical study was to get information of the composition of ONKALO’s groundwater before the construction will disturb the chemical condition. The groundwater samples were collected from the open hole without any packers. The collected groundwater samples were analysed in different laboratories.

pilot hole, ONKALO, core drilling, drillhole measurements, flow logging

Drilling and the Associated Drillhole Measurements of the Pilot Hole ONK-PH9 (pdf) (17.4 MB)