MRM conducts geophysical surveys in a number of infrastructure and construction projects. These can be roads, railways, bridges, houses, factories or other facilities. Geophysical methods have their benefits and by using the correct method in the correct context, major savings can be made in many projects. Geophysical measurements determine the stratigraphy and rock levels upon surveys ahead ofe.g.,new road and railway stretches, cable routing or the planning of new residential areas. Furthermore, geophysical methods are used to localise buried cables and cisterns, as well as dumped refuse.
Ground Penetrating Radar
Ground penetrating radar (GPR) is a method for quickly mapping deep within the rock and stratigraphy along interesting stretches, for example, cabling paths, new road lines or areas that are of interest for gravel and rock quarries. The method can also be used to localise dumped or buried objects, such as cisterns.
A transmitter sends electromagnetic signals into the ground. The signals are reflected against the rock surface and other layer boundaries, and the result is then shown in the form of a radar echo on a screen. If the GPR survey encompasses several survey lines within a delimited area, a 3D figure can be interpolated.
Refraction seismic acquisition allows to obtain information about stratigraphic thickness, as well as the propagation velocities of seismic waves through these layers. The velocities can in turn be correlated to different soil types. Furthermore, information is obtained with regard to cracks and crush zones in the bedrock.
The method is based on the analysis of refracted seismic waves in the ground, as seismic waves have different propagation velocity in different soil and rock materials. Normally, propagation velocity increases with depth. Non-cracked rock, which serves as a reference, is characterised with the highest velocity.
Geoelectric, Electromagnetic and Magnetic Measurements
By using resistive measurements, the electrical conductivity of
the ground can be determined. The more free ions there are in the
ground, the higher the conductivity. This can be used, inter alia,
to map out contamination plumes, since the groundwater there often
has higher conductivity.
Electromagnetic measurements can, for example, be used to localise crush zones in the bedrock. The crush zones contain water and normally conduct electric current better than the surrounding rock. The measurement is conducted by means of an electromagnetic field being sent into the ground by a transmitter. The field is then measured by a receiver and after interpreting the effect of the field, any crush zones can be localised.
Magnetic measurements can be conducted,e.g., in order to localise lithologic contacts and crush zones. This makes the method suitable for localising suitable locations for drilled wells or lithologic contacts for tunnel projects. The method is based on the principle that different types of rock have different concentrations of magnetic mineral. In crush zones, the concentrations of these minerals are often lower than in the surrounding rock, which creates anomalies.