Geophysics – a versatile tool for ground investigations
Published 2010-02-15 00:00:00 | Updated 2010-02-15 15:41:10
For more than a hundred years, geophysics has been instrumental to the mineral exploration industry, which was the target already at the beginning of the geophysical science sector. The challenge for the geophysical community is now to widen its scope into other earth science sectors.
The urge to know more about the subsurface is increasing at a high pace and a high pressure is imposed from all sides of our society. The search for more fossil fuels globally is pushing the development of geophysics further on. The ever increasing population and the growing metropolitan clusters forces developers to exploit land that was earlier considered to be unsuitable for settlement. In many cases, houses are today built on polluted plots or land with inferior geotechnical properties. Another threat that lurks around the corner is global warming. What will the consequences of that be? All indicators are pointing at an Earth undergoing some dramatic changes.
Geophysical tools have proven to be versatile in the exercise of collecting more detailed information about the subsurface. A traditional ground investigation may involve digging a hole in the ground or making a geotechnical drilling. Both of these methods will give full and detailed information. However, there is one major drawback with them both. The information gathered is from single points and you cannot tell what happens outside and between these points. Non-destructive continuous information such as geophysical measurements is one of the most cost efficient methods to fill in the gaps. A combination of geotechnical and geophysical investigations will allow a project to run with an increased quality control. This will result in a better control of measures to be taken and that the involved costs can be determined beforehand.
The environment is a concern of today. Since most pollutants will in some way differ from the natural properties of the ground, it is possible to map them using geophysics. A threat to nature can for example be a leaking waste dump. By geophysical monitoring such a leakage can be discovered early and its negative effects to nature and humans can be minimized.
For all construction sites that involve interaction with the ground, it is of outmost importance to know as much as possible before commencing the project. For example, if a tunnel is to be made through the rock, it might prove to be less costly to let the tunnel make a turn around weakness zones detected by a geophysical investigation. Should the project demand that the tunnel is made at a fixed position, the geophysical pre-investigations will allow the project designers and decision makers to be prepared and to make the right crucial choices, which may be the difference between success and failure for the project.
Another example that would save considerable money and effort is if a pipeline is to be dug into the ground. In this case, it is of importance to know that enough depth clearance is available, without having to blast the rock. This is even more interesting if, for example, a sewer pipe is to be dug in. A pipeline or a supply pipe is normally pressurized and the fluids will flow in the right direction due to pumping and thus the pipeline can follow the surface topography with its highs and lows. For a sewer pipe dug in, the transport of the fluid is dependant on the inclination of the pipe and the gravitational pull. Thanks to good planning and finding the best possible route, the need of pumping stations and similar installations is minimized and costs are kept at a minimum.
The geophysical science is still developing, but has come far in being a helping hand to projects involving rock and soil. While some methods have reached a point of acceptance within the civil engineering sector, there are still more to come. One of the first “modern” geophysical methods, first described about a century ago, has gained a lot of attention during the latest decade and a half. Geo-electrical methods measure the possibility to conduct a current through the ground or the ability for the ground to hold an electrical charge for a period of time. A phenomena known as spontaneous currents can also be picked up and used.
An application that has proven very successful is the on-shore oil exploration down to a couple of hundreds of meters. Oil exploration is an expensive exercise, be it on-shore or off-shore. Looking for shallow oil finds, on-shore geo-electrical methods are used for overview mapping and to pinpoint locations of further interest, where the investigations should be further detailed using alternate methods such as test drilling. The same geo-electrical methods can later on be used during the build-up phase, both for the extractions site and the infrastructure installations for distributing the product. Later in the life of an on-shore oil well, geo-electrical methods can be used to trace the eventual pollutants around the site. As geo-electrical methods lend themselves well to monitoring, they can also be used for surveillance of critical leakage points along a pipe line.
For more information about the versatility of geophysics as a tool, visit www.abem.se.
Tags: Management & Consulting
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