45 1. Shear velocity measurement in boreholes • PSSL logging is suitable for a borehole going through a “slow” formation, the hole of which is uncased, and which is supported by bentonite-based fluid, • Acoustic logging is suitable for “fast” formations, i.e. bedrock. The continuity between cased and uncased hole measurements was ensured by a downhole section in an open hole (see orange dotted line on the “downhole log” in Figure 1.31); it would also have been possible to carry out a PSSL in a cased hole. Log Vs Figure 1.31 Vs log (red) obtained from a downhole, PSSL and a “FWF sonic”. The continuity between the measurements in the slow and fast formations was ensured by the recording of Stoneley waves, which are very clear between 55 and 160 m (see orange dotted line on the “sonic log” in Figure 1.31). The final log combines the downhole measurement between 0 and 50 m, the PSSL measurement between 56 and 225 m and the acoustic measurement between 225 and 280 m (see orange rectangles in Figure 1.31).
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