Geophysics a versatile tool for ground investigations

It’s availability and accessibility has been enhanced thanks to developments of both hardware and software. The urge to know more about the subsurface is increasing at a high pace. A high pressure is imposed from all sides of our society. A global search for more fossil fuels is pushing the envelope 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 exploitation. 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 these methods will give full and detailed information. However, there is one major drawback with both. The information gathered is from a point source. A question that immediately arises is – What happens outside and between the points of information? Non-destructive continuous information, ie geophysical measurements, is one of the most cost efficient methods 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 follow on costs involved will not come as a surprise but is determined beforehand.

Environment is a concern of today. Thanks to that 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 on and its negative effects to nature and man 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/decision makers to be prepared and make the right crucial choices, which maybe is the difference between success and failure for the project. 

Another example that would save a lot of 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 the need for blasting of 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 incline 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 a minimum.

The geophysical science is still developing but has come far in being a helping hand to projects involving rock and soil. A sector that has not been mentioned is the mineral exploration. However, this was the target already at the onset of the geophysical science sector. For more than a hundred years geophysics has been instrumental in this sector. The challenge for the geophysical community is now to widen its scope into the other earth science sectors as well.

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 that were described first time 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 if the ground can hold an electrical charge for period. 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 is used for overview mapping and to pinpoint locations of further interest where the investigations should be further detailed using alternate methods 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 it self well to monitoring it can also be used for surveillance of critical leakage points along a pipeline.

For more information about the versatility of Geophysics as a tool and what we can help you with contact:

ABEM Instrument AB
Mats Thörnelöf
Marketing & Sales Manager
Phone: +46-8 564 88 300
Fax: +46-8 28 11 09
E-mail: mt@abem.se
www.abem.se