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Geophysical Prospecting

Our geophysical prospecting studies allow us to indirectly measure the physical properties of soils and rocks.

We offer the following geophysical methods:

  • Geoseismic Prospecting

Cross-Hole Test (CH).

Ambient Vibration Test (VA)

Dispersion In Seismic Surface Wavest (SPAC).

Down-Hole Test (DH).

Multichannel Analysis of Surface  Wave (MASW)

Seismic Refraction Tomography Test (TRS)

  • Geoelectric Prospecting

Vertical Electric Sounding (VES)

Electrical Resistivity Tomography (TRE)

  • Thermal prospecting

Thermal Resistivity

  • Ground Penetrating Radar (GPR)

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Committed to Quality and Results

Geoseismic Prospecting

Cross-Hole Test (CHT).

The Cross-Hole method is widely used for the determination of “P” and “S” compressional wave velocities, as well as the Poisson’s ratio and the shear modulus G and dynamic elastic modulus E.

It is sometimes it is also used for possible anomalies between wells and characterization of defects in shallow and deep foundations.

Ambient Vibration Test (AVT)

 

It has been demonstrated that the use of microtremor in the technique of spectral ratios H / V, is a very useful tool to estimate the site response, that is, the fundamental frequency of the terrain, useful in urban areas. The H / V methodology records the natural noise at a site by using triaxial broadband sensors (geophones). The interpretation of the measurement of natural vibrations is based on the assumption that the spectral quotient between the horizontal components and the vertical component of the microtrepidations is an approximation of the transfer function of the soils, and at the moment the high resolution of the H / V technique is indisputable for the determination of the terrain’s fundamental period.

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Dispersion In Seismic Surface Waves

 

The Spatial Autocorrelation Method (SPAC) is a passive seismic technique that is based on the analysis of several microtremors records obtained at the same time, in an arrangement of four to seven independent stations.

The objective of this technique is the calculation of the phase velocity for each frequency detected in the seismograms to estimate the structural model of velocities from the microtremetric record.

The method assumes that all microtremors are basically composed of surface waves and that they are stationary in space and time.

Down-Hole Test (DH).

 

The Down Hole Test allows the determination of the speed variation of seismic wave propagation with depth, through low-strain tests carried out in situ. For the execution of the Down Hole test, a source of seismic excitation is generated from the surface. The disturbance induced in the soil is recorded at depth through a geophone that is introduced into a prepared borehole (cased with hydraulic PVC and the annulus filled with cement grout between casing and the sounding wall). The geophone records the seismic movement and sends the signal to a seismograph where it is amplified and digitized.

Multichannel Analysis of Surface Wave (MASW)

 

The MASW method is a technique that makes use of the dispersive properties of surface seismic waves (Rayleigh waves). The frequencies used are in the range of 1-30 Hz and the research depth can reach, up to several tens of meters.

The survey uses 4.5 Hz geophones to register the seismic, which are positioned in a horizontal linear arrangement (without abrupt variations in the inclination) at an equidistant spacing, which can be moved to cover the study length. The seismic signal is generated from hits given on the study surface with a 12-lb. The location of the sources will be at the ends and in the middle of the geophones arrangement  for each point a seismogram will be obtained.

From the processed seismograms a dispersion curve is obtained, formed by the surface wave velocity and the associated phase frequency. Later in this curve, the fundamental mode of the signal that is characteristic is interpreted because the speed of these waves depends on the frequency.

The velocity model Vs and the depth is obtained through the numerical inversion of the data derived from the dispersion curve.

Seismic Refraction Tomography Test (SRT).

 

The seismic refraction method is based on the propagation of seismic energy through the subsoil layers, whose objective is to determine the contact between subsoil materials that have different wave velocities O (longitudinal wave).

The propagation of seismic energy through a medium is obtained from an impulse generated on the surface of the terrain, known as a point of shoot, which will cause a movement that will be detected by an array of equi-spaced receivers (geophones) and they will record it in a seismogram in which the arrival time of the P wave will be indicated to each geophone. The direct wave is the first to register in the receivers near the source, indicating the speed of the most superficial layer.

Once the arrival times have been read in each seismogram, we will obtain a dromochronic (time-distance curve) with which the velocity of each refractory layer present in the subsoil can be calculated.

Within these tests we also perform tests of thermal resistivity, redox powers and Torvane test in case the project requires it.

Geoelectric Prospecting

Vertical Electric Sounding (VES).

 

The characterization of resistivity or conductivity present in the  terrain is necessary for and optimal electrical earth system design that will efficiently protect electrical equipment and installations from unexpected overloads in the network. For this purpose, measurements of resistivity at different inter-electrodal openings are performed to determine the number of geoelectrical layers that make up the subsoil, as well as the representative resistivity of each of them.

Electrical Resistivity Tomography  (ERT)

 

The Electrical Resistivity Tomography method is a multi-electrode technique, where, conventionally, the electrodes are positioned on the surface of the ground at a constant interval laterally. The goal is to obtain the real resistivity in a 2-D shape of the different materials that make up the subsoil. The depth of the study is a function of the length of the electrodes layout.

The data obtained from the field work are values ​​that represent the apparent resistivity of the subsoil, which are obtained by the relation between the energy that is passed to the subsoil through the electrodes, the voltage difference generated by the electrical energy, which is measured through the same electrodes and the spacing between them. The apparent resistivity values, electrode spacing and length of the layout are processed in a mathematical system of data inversion, and as a result the distribution of real lateral resistivity and depth is obtained

The Tomography sections reflect contrasts of resistivity existing within the medium, which can be associated with structures or anomalies of geological, environmental or geotechnical interest.

Thermal Prospecting

Thermal Resistivity

 

It is a physical property of materials that measures the ability to resist the passage of heat.

It is very useful for the design of buried electrical wiring system. These tests are performed in accordance with the IEEE STD 442-1981 IEEE Guide for Soil Thermal Resistivity Measurements.

Georadar

Ground Penetrating Radar (GPR)

The technique of Ground Penetrating Radar (GPR) consists of the emission of radar pulses (electromagnetic radiation) at a frequency range of 10 Hz up to 1.2 GHz and maps the surface of the subsoil.

The penetration range depends on the type of antenna used.

Its main applications are for the detection of buried pipes, public utilities and environmental engineering works.

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