DMT explores subsurface of Hong Kong

Essen, Germany, 17.06.2016. In order to increase the amount of available living space in densely populated Hong Kong, one of the city's wastewater treatment plants is due to be relocated underground. The German engineering company DMT has been commissioned to perform borehole surveying using its specially developed shuttle tools for horizontal boreholes. Such geotechnical exploration of the subsoil plays a crucial role in the Chinese contractor’s planning with regard to the construction of the underground caverns.

For the survey DMT will apply a number of different geophysical measurement techniques: optical drill hole scans to investigate structure in the rock, measurements of the rock's natural gamma radiation for the purpose of lithological correlation of individual rock layers, full-wave sonic measurements for geotechnical rock characterisation and calibre measurements for determining the exact diameter of the boreholes and any breakout (stress-induced enlargements in the borehole cross-section).

"What's special and particularly challenging about this survey is the fact that the drill holes are sub-horizontal, which makes conventional surveying procedures nearly impossible," explains project manager Torsten Gorka. To overcome this obstacle, DMT will utilise proprietary borehole shuttle tools, which have a fully-integrated memory, power supply and measuring sensors. "In contrast to conventional wire-line tools, which can usually only be applied in downward sloping holes, our shuttle technology enables the use of tools at any orientation, including horizontal and even upwards."

Three horizontal boreholes of up to 1,000 meters in length will be measured in this way.