The availability of high sensitivity temperature sensors (0.001 K sensitivity platinum resistors), which can be positioned at intervals of a few centimeters along a vertical profile in the unsaturated zone, allows short-term in situ determinations-one day or even less-of the thermal diffusivity. The development of high data storage capabilities also makes this possible over long periods and the relative variations in thermal diffusivity allow the monitoring of the variations in water content. The processing of temperature measurements recorded at different depths is achieved by solving the heat equation, using the finite elements method, with both conductive and convective heat transfers. A first set of measurements has allowed this approach to be validated. Water content variations derived from thermal diffusivity values are in excellent agreement with TDR measurements carried out on the experimental site at Boissy-le-Châtel (Seine et Marne, France).

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This work presents the geotechnical and the geophysical characterizations of soil for an area forming the southeast extension of the Mila town (Marechau region). This area shows traces of ancient land movements, permanent flows, clayey lithology, and irregular morphology with a steep slope. To make decision for building it, we analyzed their soils by carrying out the core drilling tests, the dynamic penetration tests, the laboratory tests, the determination of the electrical resistivity in order to describe and to study the vertical and the lateral variability of the underlying geological formations, and measured the electrical resistivity to map the depth of bedrock roof. We also describe the three-dimensional organizations of underlying geological materials that make up the study area. The core drilling test results gave a clayey soil with limestone blocks. The dynamic penetration test shows two categories of soil. The laboratory tests confirm that the materials analyzed are clayey nature, saturated, very plastic, over-consolidated and medium to very compressible, with medium to strong swelling potential, and medium aggressiveness on concrete. The tomography results show a single layer land of a clayey nature with massive rocks embedded in it. The combination of these results with location, land morphology, tectonic and their sismotectonic aspect indicate that the area is at high-risk, and their urbanization requires rigorous and mandatory precautionary measures.

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The present study aims to charcaterize, by geophysical methods (electrical sounding and seismic refraction), the downstream part of the Oued Nador alluvial layer or deposits (Tipaza, Algeria) and the morphology of its bedrock to better locate the freshwater-saltwater limit. This will allow to better understand the marine intrusion.Indeed, the aquifer is defined by a clay and marl substratum of middle to lower Pliocene Piacenzian age rich in recent Neogene and Quaternary filling (Quaternary alluvium composed of sand, gravel and pebbles). During Spring of 2015, 2016, and 2017 three electrical surveys were conducted. The results indicate that the origin of the salinity is due to progressive marine intrusion inside the aquifer (Bechkit et al, 2017; Bechkit et al, 2018a; Bechkit et al, 2018b). However the presence of clay makes the contrast between the saltwater and the clays less important so that it is difficult distinguish electrically the two mediums. In May 2018, we combined both electrical survey and a refraction seismic acquisition on the area of study. This work was carried out in order to separate, through the ranges of wave propagation velocity, the saltwater formations from the clay ones. The presence at a certain distance from the coast of an elevation of the clay bedrock has an advantage. Indeed, it acts as a natural barrier against any intrusion on a large scale of saltwater at depth. The study carried out in this context showed that the combination of two geophysical methods is very useful in environmental study for the evaluation of the salt water intrusion in an alluvial ground in the presence of clay formations.