Detection de fuite dans les barrages en remblai par la methode de polarisation spontanee et par tomographie electrique: Cas de la jonction de deux barrages en remblai.

摘要

The infiltration through the core of foundation of embankment dams is a problem which is worrying for safety and economical dams. The mechanism of infiltration can be progressive and can disturb the stability or the durability of the structures. Consequently, its evolution can undermine public security. Statistics made for 11192 embankment dams through the world showed that until 1986, 48% of damages have been caused by internal erosion. This internal erosion was generated by infiltration through the core or the foundation of embankment dam. Electrical, electromagnetic and thermometric methods are usually considered as investigation methods.;The goal of this work is to study the sensibility of the self-potential method (S.P.) to detect seepage for the case of embankment dams. We used S.P jointly with electrical resistance tomography (ERT). To attain this objective, we acquired self-potential and resistivity data with periodic changes of the water level in the reservoir. These changes were made every spring (in November) and every summer (in April) at the emptying and impounding of the reservoir. For this project, measures have been conducted over a period of two years (2008-2010). Before that, thermometry, self-potential and magnetic methods were applied on the site to acquire information about seepage and its approximate position. Flow rate was also measured. In April 2010, injection of grout was used to clog seepage.;The measurements allowed to represent the variation of potential with time and space. That permitted to make a distinction between different sources of self-potential signal. The mapping of the electric potential during the emptying and the impounding of the reservoir showed a negative anomaly which correlate to an outflow located in the upstream of the dam. The monitoring of the S.P. signal permitted to dissociate an anomaly zone which can be related to the site of injection of grout. The gradient of self-potential decreased with the increase of pressure gradient. We have computed the effective electro kinetic (EK) coupling coefficient of the dam from the variation of the potential with water level. Time-lapse ERT is used to control the variation of electrical conductivity of the material together with changes in water level. The anomaly in the time-lapse represented agrees with the outflow. We also propose a 3D numerical model to interpret the measurements in a semi-quantitative manner.;Comparing between results of modeling and the survey data, differences are noted that can be explained in different ways. More work would be needed to elucidate those differences, in particular with the measurement strategy and the estimation of coupling coefficients. Nevertheless, the proposed approach allowed to underline different variations under the ground. These results have also been used to discuss the limitations of the self-potential method applied to detect seepage in the dam.