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In conjunction with the rock tunnel construction through the Hallandss Horst, south-western Sweden, bore holes and corresponding cores were available for comparison with logging data. Two core drilled bore holes were investigated with the total core length of 370 m. Rock cores were classified, i.e. rock type, joints and weathering, and compared with bore hole geophysical measurements. The rock mass is a mixed crystalline formation with gneiss, gneiss-granite, dolerites, amphibolites and metabasite. In some parts the rock mass is rather heavily jointed and fractured and in some parts also chemically weathered. The logging setup used was natural gamma, caliper, a variety of resistivity probes and temperature. When comparing rock classification with the response from the different geophysical probes the correlation and particulars are remarkable.
Fractures and weathered zones are evident in the resistivity logs and in the caliper log. Whereas lithology changes are visible in gamma log and to some extend in the resistivity log. This strongly supports the usefulness of geophysical bore hole logging of crystalline bedrock. It also emphasizes that logging of non-cored bore holes, in e.g. percussion bore holes, might reveal very useful information especially when there are a few cored drill holes to correlate with.
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