Geological anomalies detection (DCOS)
- Cavities (voids, karsts, partially filled…)
- Water circulation
- Under consolidated areas
- Breaks of tabularity
The DCOS method is based on a statistical analysis of the surface wave energy distribution and does not need any numerical model inversion (there is no hypothesis about the geology of the ground).
Site test: geophysical methods comparison
A test area has been defined in order to compare 4 geophysical approaches to localize cavities:
Geological anomalies are represented with cold and warm contour colour.
The four boreholes are indicated by black crosses.
- F1 has shown a void between 14 and 18 meters of depth. It is based on an altered level of limestone.
- F2 performed in neutral are did not show anything.
- F3 has revealedthepresence ofan aquifer.
- F4 crossed a disturbed zone composed of earth works
This method of Electrical Resistivity Tomography prospecting called dipole-dipole consists in injecting into the soil a direct current by means of two transmitting electrodes and measuring a potential difference between two remote receiving electrodes.The results have failed to implement drilling controls.
The four boreholes are indicated by red circles.
DCOS: survey results examples
French railways at constant depth (10 and 15 m)
The results in vertical profiles are used to represent in 2D the slices at constant depth (10 and 15 m for the example presented here below). The geological anomalies are represented using cold and warm contour colour.
The equipment used has permitted to perform the measurements inside and outside of the oil tanker to keep the continuity.
Bernay (underground quarry), depth investigation 30m
On a site test, the measurement has permitted to show the geological anomaly connected to the presence of underground quarry located at 27 m of depth.
The geo-referenced 2D results permit a 3D visualization in order to emphasize the connexions between the geological anomalies.