LOCATING A SUBSURFACE OIL LEAK USING GROUND PENETRATING
here to obtain the full publication(Adobe PDF format)*
(Eighth International Conference on Ground Penetrating
Radar, May 2000)
Martin L. King
An underground high voltage cable, in which
pressurised mineral oil is used as an insulating medium, was known
to be leaking oil at one or more locations along its 2.5 kilometre
length. It was impractical and even dangerous for the most part
to dig along the cable route in an attempt to find the location
of this leak or leaks. It was known that a significant quantity
of mineral insulating oil had left the cable and entered the soil
at the site of the leak.
It was decided to trial ground penetrating radar
by scanning along and over the buried cable to attempt to pinpoint
the site of the oil leak.
Soil dielectric properties are largely determined
by the moisture content so that where moisture is displaced by
oil the soil dielectric properties will change. Soil stratigraphy
seen using radar is due to a large extent to the variable moisture
content in the layering of the soil.
Where oil is dispersed through the soil, it
will tend to displace moisture. This dielectric property change
makes the area sufficiently anomalous so that it can be detected
utilising ground penetrating radar.
This principle has now been successfully used
on a number of occasions in New Zealand
RADAR INVESTIGATION OF A FAILING CONCRETE FLOOR SLAB.
here to obtain the full publication (Adobe PDF format)*
(International Symposium Non-Destructive Testing in Civil
Engineering (NDT-CE), Sept 2003)
Martin L. King, Dany P. Wu and
Dr. David C. Nobes
At a New Zealand wastewater treatment plant
there are several large wastewater settlement tanks that are crucial
to the operation of the plant. These concrete tanks are 50 metres
in diameter and 8 metres deep with the base of each tank approximately
seven metres below ground level.
It was discovered that the base of one of these
tanks had become distorted resulting in its failure to carry out
its function. This presented a major problem for two reasons:
- The importance of the tank to maintaining sufficient throughput
of the overall operation.
- The danger of contamination of the subsurface water aquifers,
which are the main potable water supply for the area, should
a tank base failure occur.
Any plans made to repair this problem was faced
with a major restriction. Due to the type of construction of these
tanks the floor could not be cut into, or disturbed, to any significant
extent without risking catastrophic failure.
Ground penetrating radar was used to accurately
pinpoint the areas below the base of the tank where voids, which
were the root cause of the tank floor distortion, had formed.
The information provided using ground penetrating radar enabled
grouting repairs, through the floor slab, to be carried out using
precisely positioned small diameter holes thus avoiding the risk
of catastrophic failure of the tank base.
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