Thermal conductivity (λ) is a material-specific characteristic. It indicates the amount of heat flux through thermal conduction.

The LTPS’s department of geophysical tests has the following equipment:

• CRU01 monitoring and reading unit branded Hukseflux
• Thermal Sensors;
• TP09 heating probe;
• An LN01 lance (1.5 m);
• High-performance processing and interpretation software (Hukseflux CRU01); The thermal conductivity method is applied in:
• Measuring soil thermal conductivity and resistivity;

Scope

Measuring soil thermal conductivity is performed using a thermal shock probe. It consists of two parts:

• A cylindrical resistive element in which a constant amount of heat is dissipated by the Joule effect throughout the measurement;

• A temperature calculation probe placed at the soil-probe interface.

The time-domain electromagnetic (TDEM) method allows for the reconstruction of the actual resistivity distribution of the subsurface at up to 300-400 m depth.

The LTPS department of Special Tests has the following electrical equipment:

• Walk TEM 2 RX unit branded ABEM;

• Walk TEM 2 20 A TX transmitter branded ABEM;

• 40x40 m transmitter loop;

• RC-200 receiver loop.

The investigation depth depends on the equipment used and the nature of the ground.

PRINCIPLE OF THE METHOD

The TDEM method is based on the phenomenon of transient electromagnetic field diffusion. This field is created by the sudden interruption of a current flowing in a transmitting loop. This primary electromagnetic field creates eddy currents in buried conductive objects. These induce a transient secondary magnetic field measured by one or two receiving loops during the interruption.

It is applied in :

• Geotechnical investigations and soil studies.

• Groundwater investigation.

• Bedrock depth.

• Grounding;

• Cathodic protection;

Advantages of the TDEM method:

• Significant investigation depth.

• No contact with the ground (avoiding high soil contact resistance problems).

• Good penetration into conductive environments.

Geological radar is a geophysical prospecting method based on the propagation and reflection of electromagnetic waves.

LTPS's department of geophysical tests has the following electromagnetic equipment (Geo Radar):

• SIR-20 unit branded GSSI;

• Antennas of various frequencies

Application	Antenna	Investigation depth
Concrete	2.6 GHz	0-0.3 m
Road	2 GHz	0-0.5 m
	1 GHz	0-1 m
Geology	400 MHz	0-4 m
	200 MHz	0-8 m
	100 MHZ	0-20 m

• Logiciel de traitement très performant (RADAN 6.0) ;

Scope

-A transmitting antenna sends very short pulses into the ground or civil structure at frequencies ranging from 16 MHz to 2.6 GHz.

-When waves encounter contact between two horizons with different dielectric permittivities, some of their energy is reflected, while some penetrate more deeply. - A receiving antenna receives the directed, reflected, and refracted waves.

It is applied in :

• Pavement surveying (measuring thicknesses, anomalies, etc.);
• Underground network detection (cables, pipes, metal objects, etc.);
• Archaeology and geology (cavities, basement, etc.);
• Concrete and bridge deck surveying (detection of reinforcement, etc.);

What does Geo Radar measure?

• GPR measures the trip time and amplitude of reflected, transmitted, and/or refracted EM waves between the transmitter and the receiver.
• The amplitude and trip time of EM waves depends on the permittivity and conductivity of the horizon they pass through.
• The amplitude of an EM wave measured at the receiver depends primarily on permittivity contrasts.

Seismic methods are based on the study of ground mechanical wave propagation. Wave propagation velocity depends on the elastic properties of the materials.

The LTPS’s department of Special Tests is equipped with:

• Seismogram branded DAQ Link 3;

• Two 12-track coils (up to 10 meters);

• Downhole well probes;

• Crosshole seismic source;

• processing and interpretation software of High-performance (SeisImager)

The seismic prospecting method is applicable for:

• Determining layer velocities and thicknesses;

• Measuring dynamic moduli;

Scope

The principle of the seismic method consists of causing a ground tremor using a source (hammer, dynamite, etc.) that creates a vibration wave that propagates in all directions. Then, using geophones, the arrival of some waves (compression, shear, etc.) is recorded.

Different Techniques

LTPS's department of Special Tests offers three different seismic techniques:

• Seismic Refraction

• Downhole

• Crosshole