ABSTRACT
Obtaining a clear image of the subsurface in front of the Tunel Boring Machine (TBM) is one of the main objectives to increase safety during tunnel drilling in soft soil. Before construction, geotechnical and geophysical surveys from the surface give a good impression of the soil structure and heterogeneities. During construction, more information can be obtained by installing a seismic system on the head of the TBM. Traditional data processing techniques do not lead to accurate images of the subsurface. The limited number of receivers causes artifacts. Special focusing techniques have been developed with a weighted least-squares optimization, to take this problem into account and improve the image of the area of interest.
