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[Observatoire Gravitaire Géoazur] ERT

Since 2006, the landslide has been equipped with a permanent SYSCAL resistivimeter connected to a 24 electrode flute with a 120 meter electrical line (one electrode every 5 meters). The resistivimeter is connected to a computer scheduled for running a dipole-dipole measurement every day at the same time. The device enables the acquisition of 574 measurement points per day in the form of a 2D resistivity pseudo-section. Thereby, at the present time, the recovered database represents more than 1,000 acquisition days.

A standard approach for data processing is not possible. Consequently a former research study was carried out concerning the variables that are statistically acceptable for representing a measurement day. The work is done mainly with the values of daily average resistivities allowing to observe resistivity variations, which are function of water presence in the massif.

The purpose of such a device is the observation of resistivity variations within the massif day by day. In fact, a same profile may change according to groundwater contents and consequently according to rainfall and water seepage. The device allows to highlight the preferential creepage of groundwater at the bottom of the landslide (the most active zone and corresponding to flow direction).

A daily measurement with the Wenner-Schlumberger method was added to the dipole-dipole measurement at the same time. The purpose of the second measurement is on one hand to get additionnal measurement for the same day and on the other hand to obtain a different representation of the landslide (the dipole-dipole method fitting for locating vertical structures whereas less appropriate concerning horizontal structures).

From a technical point of view, the future objectives related to the ERT installation are the transfer of data directly to the Geoazur laboratory for immediate and automatic data processing, and the enlargement of the electrical flute in order to cover the whole cross section of the landslide.

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article rubrique
Tuesday  15 December 2009
traduction [English ] [français ]
Geophysical Location
Location of the permanent electrical tomography Read the whole article
Tuesday  22 December 2009
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ERT Parameters
Tomography recordings: Acquisition mode: permanent SYSCAL resistivimeter connected to a 24 electrode flute, i.e. a 120 meter long electrical line. Acquisition of 574 measurement points (...) Read the whole article
Friday  18 December 2009
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Time Lapse Survey
Evolution in time of a pseudo-section and subsurface hydraulic response to a rainfall event - 1 profile per day over a 13 day period - Evolution in time of a pseudo-section and (...) Read the whole article