Borehole geophysics for a lock replacement project - Limmel - NL
Borehole geophysics for a lock replacement project
Due the necessary replacement of the Limmel lock on Julianakanaal, the Client has contacted G-tec to undertake a geophysical borehole survey on both riverbanks. The aim of this study was to characterize the sub-soil conditions with regards to weathering and permeability.
A total of ten boreholes to thirty meters depth have been investigated by geophysical methods and logging tools. Borehole seismics (crosshole tomography of P waves) allow investigation and mapping of the sub-surface seismic velocities. The techniques highlighted the main lithologic structure and the degree of weathering in the Chalk formation. Natural gamma measurements have been undertaken to record the clay content of soil/rock formation, these have given key information on the presence of clay layers and allow correlation between the different boreholes and the two riverbanks. On a smaller scale (plurimillimetric level), optical televiewer inspections have been undertaken to have more accurate information on the Chalk formation and its discontinuity profile (orientation and inclination). Optical televiewer has been also used to record the borehole deviation and assist in the processing and interpretation of borehole seismic data.
Both methods were complementary and gave consistent results.
At the end of this survey, a preliminary geological model of the underground has been provided to the Client with interesting information on permeability and weathering of the Chalk formation.