Natural stone assessment with ground penetrating radar GPR

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Natural stone assessment with ground penetrating
radar (GPR)

• The 15th Meeting of the Association of European
  Geological Societies
• 1620 September 2007
• Tallinn, Estonia

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Natural stone assessment with ground penetrating
radar (GPR)

• Location of the study areas

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Natural stone assessment with ground penetrating
radar (GPR)

• The ground penetrating radar instrumentation
• GSSI SIR 2000 control unit
• Antennae between 40 MHz and 400 MHz

200 MHz antenna
Control unit
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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

• Porphyritic granite situated in the south-eastern
  Finland
• It belongs to the Central Finland granitoid
  complex and is described
• postkinematic in relation to the deformation of
  the area

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1
• Typical feature of the rock is a strong
  horizontal exfoliation type fracturing (height of
  the bench about 5 m)

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

• GPR measurement traverse of 65 m in length
  (vertical and horizontal scale are equal)
• The profile was corrected with altitude data to
  present the actual surface and fractures
  orientation

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

• The GPR was able to detect the major horizontal
  and sub-horizontal fracturing

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

• Vertical or near vertical fractures were
  difficult to detect due to their small reflection
  surface towards the measuring antenna

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 1

• The horizontal fractures near the surface were
  sometimes strongly weathered providing space for
  surface water to collect
• Those spots were detected as individual targets
  on the radar measurement profile
• The spots can be thought to be reflections from a
  sub-horizontal fracture zone near the surface

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 2

Soapstone situated in North Karelia It belongs to
an Archaean greenstone belt, in the border zone
between the Archaean area and the
Palaeoproterozoic North Karelian Schist Belt
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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 2

Typical North Karelian soapstone Sample size 260
mm x 200 mm
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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 2

Soapstone quarry in North Karelia
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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 2

• With the soapstone, the measurements revealed
  more of the internal structure of the rock,
  making the detection of the fracturing complex
• Especially internal lineation was quite well
  visible in those sections where the stone
  contained more conductive minerals.

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Natural stone assessment with ground penetrating
radar (GPR)

• Study area 2

• Large open horizontal fractures were detectable
  also in this stone type, which can be helpful in
  planning of the quarrying operations.

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Natural stone assessment with ground penetrating
radar (GPR)

• Conclusions

• Ground penetrating radar (GPR) is suitable for
  large-scale quality assessment of natural stone
  deposits and quarries
• The measurements are easy and quick to do and the
  preliminary results can be evaluated immediately
• The fracture detection level varies depending on
  the used equipment, mainly on the frequency
• The development in GPS technology has made it
  possible to position the measurements accurately
  and thus trace back the results into the quarry
  to help extraction planning
• The differences in the measurement results and
  their interpretation found among these two rock
  types indicate the importance of knowing the
  electromagnetic properties and mineralogy of the
  stone
• Also knowing the geological structure and other
  characteristics of the stone beforehand helps to
  avoid false interpretations