Site Uniformity Borehole Seismic Testing

Seismic coupling to the surrounding earth materials is achieved by filling the hole with water or drilling fluid. The in-hole detector array remains fixed throughout the test and intervals of 22m or 46m of the borehole are tested to depths in excess of 150m.

Seismic energy is normally generated with an impact source at closely spaced locations extending from the borehole to distances of at least equal to the depth to the deepest inhole detector. This provides an approximate radius of investigation for the SUBSÓ test which is equal to the hole depth.

Seismic waves that travel from each surface source point at varying angles to the in-hole detector array are recorded on a digital seismograph and stored on computer disk for later processing and seismic image production. The output of a SUBSÓ test is a Seismic Tomographic Image (STI).

Coffey Geotechnics provides equipment and trained field personnel to carry out SUBSÓ. The seismic data are processed and interpreted using STI supplemented by geotechnical information and calibration at the borehole. 3D subsurface information is obtained by combining seismic scans in different directions.

Applications:

• non-destructive site uniformity assessment
• expands range of investigation of borehole
• detects undermined and cavernous regions
• locates geological structures
• identifies changed tunnelling conditions
• grouting effectiveness assessment.

Technical Documents