These factors have caused utility engineers and contractors to search for alternative methods to locate subsurface structures, often with mixed success. There are several geophysical techniques with proven capabilities in non-intrusive subsurface investigation, but there are less publicized limitations to these methods that potential specifies and users should be aware of if they are to avoid inconclusive or misleading survey reports.
Practical Near-Surface Techniques
The real driving force behind the development of geophysical survey methods was the search for oil and other valuable mineral deposits. The earlier methods were therefore primarily focused on the detection and identification of relatively large geological formations at depths that were typically measured in several hundreds of feet. Such methods do not have the resolution to detect small objects, such as pipelines and cables, buried only a few feet deep.
A few methods, however, were either developed specifically for near-surface work, or were readily adaptable to the task of locating relatively small objects at shallow burial depths. The most commonly used methods in current utility location practice are:
Ground Penetrating Radar
Magnetometer/Gradiometer
Non-contact Conductivity
Specialized Utility Locators
These methods have been proven to be very effective in the right conditions, but all have limitations that can render them inconclusive, or worse still, misleading, if used or interpreted by an inexperienced operator.
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2016-02-26
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