Q

Is it necessary to do additional scans with the emitter and receiver somewhat offset in the vertical plane when performing tomography analysis on cross-hole sonic logging data?

A

Generally, additional data should be obtained from offset scans whenever parallel (not offset) scans exhibit defects. Regardless of defects, offset scans of diagonal profiles for shafts with 6 or more tubes are unnecessary. The TomoSonic software can provide results from only the parallel scans. The software will use offset scans, if available, to improve results. These scans are particularly helpful around the perimeter.

Often, an offset distance of about 300 mm (1 ft) to a maximum of 500 mm (1.6 ft) is enough. It is possible to obtain the additional offset scan data later. Nevertheless, this procedure requires obtaining data using the same Pile Name. It is advised that engineers immediately collect the extra offset data, if a defect is suspected, while the probes are still in the tubes.