Also Click here to visit the manufacturer Olson Engineering in the USA

Click here to visit the Olson Instruments Website in the USA

Borehole Seismic Source

Applicable On:Subsurface Karst/Sinkhole, Soil and Rock, Concrete
and Embankment Dams, and Concrete Foundation/Rock Interace Studies

Test for:Velocity Tomogram Images of: Subsurface Voids and Caverns, Rock Competency, and Voids, Honeycomb, Cracks, Uncured or Weak Concrete

The Olson Instruments GEOT-1 system consists of a string of 8 hydrophones at 1-2 m spacings (typical) as shown and a sonic piezoceramic or mechanical source (not shown). The hydrophones have waterproof connectors, and are downhole amplified for high sensitivity. The hydrophone string plugs directly into modules on the the Freedom Data PC for data collection. The 8 channel amplified hydrophone string is thus suitable for travel time (velocity) tomographic imaging of subsurface conditions for geophysical engineering purposes, and can also be used for faster Parallel Seismic tests of more massive deep foundations (see Foundation section). If more powerful sources are needed, custom electrical/mechanical sources can be developed.

The ability given by Crosshole Tomograhy testing and analysis is the ability to see the shape of an anomaly such as karst voids in sinkhole studies to better judge its extent and severity between each tested cased borehole pair. Our geotomography systems have been used in karst studies, abandoned coal mines, concrete dams, bridge footing/rock interface studies to image massive concrete and subsurface soil and rock conditions with velocity tomography.

As an example of the geotomography results from the use of the GEOT-1 system, a tomogram from between two coreholes through a concrete footing foundation into the underlying shale bedrock is shown below. The 2-D tomogram clearly shows the bottom of the footing concrete as the faster velocity material from 0 to about 2.5 meters on the Z depth axis. Zones of slower velocity, medium hard shale to faster velocity, hard shale bedrock are also shown below the footing. The velocity scale on the right is in units of meters per millisecond, so a value of 4.0 equals 4,000 meters per second.