Use of the Acoustic Scanner for Geotechnical Investigations

The acoustic scanner (or acoustic televiewer) is a geophysical tool capable of providing oriented acoustic images of a drillhole wall. It is being increasingly used in geotechnical investigations to determine the orientation of rock mass defects. Acoustic scanning was recently carried out at Roxburgh Dam, New Zealand, where two 60 m deep cored holes were drilled in schist rock. The holes were scanned and the data processed using proprietary software. A detailed comparison was made between the drill core and scanner images. The images produced clearly showed the major rock mass defects present, enabling their true dip, azimuth, and approximate thickness to be determined. Acoustic scanning was subsequently used at the site to rapidly and cost effectively determine the presence and orientation of defects in 37 non-cored foundation drainholes.

Acoustic scanning has considerable potential for use on geotechnical projects where defect orientation is a prime objective. It may be used in conjunction with core drilling to provide high quality geotechnical data and with non-core drilling to provide cost effective spatial coverage or data “infill” between cored holes. In some situations the scanner may also be used to estimate in situ stress orientations from analysis of drillhole breakout.