A series of about a dozen soil borings combined with seismic surveys should, over the next two years, determine the exact geological composition of the soil within the search area of the Einstein Telescope. One drilling in the Walloon town of Aubel has just been completed.
That drilling will take place scattered over the search area for the telescope in Wallonia, Flanders and (Dutch) South Limburg. The soft attenuating soil layer in the area with the hard underlayer make the soil suitable for building the underground observatory. In addition, drilling and seismics are needed to map specific information about the soil layers. Therefore, the drilling is not intended to determine exact locations of the three underground vertices.
Drilling will be done to an average depth of 250 meters. This is necessary because the Einstein Telescope will be built 200 to 300 meters underground. The average duration of drilling is four to six weeks. Once the locations are finally determined, the permitting process and communication with the surrounding area will begin. The intended locations are in the outlying area.
The first drilling in Aubel, Wallonia, commissioned by the University of Liège, was recently completed. It was drilled to a depth of 250 meters. The next drilling is planned starting in the fall. There is no exact order yet, partly because the results of an earlier drilling will influence the choice of the next drilling. Depending on the analysis of the ten borings, it may be necessary to carry out several additional borings.
Whereas the borings provide a picture of the soil conditions at that location itself, seismic provides insight into the soil quality between those drilling locations. In seismics, sound waves are sent into the soil. The reflection of those waves teaches how the layers in the soil are constructed.
The program involving drilling and seismics was developed on behalf of the Einstein Telescope project office. In addition to its own experts working for the project office from Nikhef, TNO is also contributing to supervising and testing the implementation.