GEOPHYSICS

This is a technique using devices with four electrodes that inject current into the terrain and the difference in the potential generated is measured.
With this, the resistivity of the terrain is calculated and its lateral and depth variations are recorded, interpreting the structure of the subsoil.

We also use techniques such as vertical electric sounding (VES), by which one-dimensional models of resistivity and depth, are obtained.

Methods of electric tomography are also applied, which provide two-dimensional profiles.

For all of this an IRIS J-R1 two-channel resistivity meter is used, which has a maximum output power of 200 W and maximum voltage of 600 V.

For geotechnical purposes high resolution seismic or surface seismic is usually used. With an energy source that is not overly powerful (the impact of hitting a hammer) seismic waves are generated which are recorded in different stations (geophones) distributed over the terrain. Through the study of different wave forms and their travel times, it is possible to obtain seismic images of the subsoil that are subsequently related to the geotechnical levels.

Using the seismic refraction technique an image of the subsoil is obtained in terms of the field of seismic velocities (P waves). It aims to determine the structure of the subsoil, as well as find out about the state of a hypothetical rocky substratum. It is also used for rippability studies.

In seismic tomography analysis, variations in the model, such as layers of low velocity or lateral variations, are not limitations. Through an iterative process of inversion, the most appropriate model is achieved.

Another possible type of seismic study is through the analysis of the surface-wave dispersion (MASW). With this method it is possible to obtain a one-dimensional model, or generate sections of terrain of S wave velocity distribution with the depth. This type of measurement if particularly useful to find out about the distribution of geotechnical levels in depth even when there are “soft” blended layers. It is also used to obtain dynamic models of earth deformation for the classification of Vs30 in seismic hazard studies.

With the Down-hole test it is also possible to obtain dynamic models of elastic earth deformation. In this case it is necessary to have a borehole into which a triaxial geophone is inserted.

For these studies GEONOR has a DOLANG DBS-280B seismograph with 24 channels and 24 bits.