A combined approach using the surface geophysical method (microgravimetric survey) and sub-surface investigations (speleology) was undertaken at an experimental karst site located in the MChentel area near Cheria town (Northeast of Algeria). The gravimetric survey, carried out by a gravimeter GNU-KC 444 during March-April 2016, allowed the procurement of 614 gravimetric measurements distributed on the whole of the zone of study. The gravimetric data shows a reduction in the values of the Bouguer anomaly between two collapses. This trend probably implies an effect of karstification that would explain the reduction in the values of the Bouguer anomaly while moving towards the centre of the zone of study. The results provided in this work of underground exploration by the team of speleologists from Polytechnic Nice-Sophia in 2013 and 2014 are particularly well illustrated by the topography of the cavities upstream and the real photographs, the micromorphology and the microstructures of the walls of the cavities explored. The joint application of the microgravimetry and speleology make it possible to evaluate the advantages and effectiveness of the microgravimetry for the detection of underground cavities. This improves knowledge of the karstic system structure of Eocene carbonates in the studied area.

This study presents the results and the interpretation of a microgravity survey realized in the MChentel zone near Cheria tone situated in the Northeast Algerian. The microgravity survey, made during April and March, 2016, allowed the obtaining of 614 measures distributed on the whole zone of study. The gravimetric data were measured by means of a gravimeter relative GNU-KC 444 were used with location and the height of stations with centimetric precision by pocket GPS and an electronic theodolite type Qeo FET 420 k. The gravimetric data measured on the ground were connected with a reference gravimetric station situated near the zone of study. On the scale of the zone of study, the gravimetric data show a decrease of the values of the anomaly of Bouguer between both collapses. This trend implies probably an effect of karstification which would explain the decrease of the values of the anomaly of Bouguer by going to the center of the studied zone. The interpretation of gravimetric data shows the presence essentially of two negative zones, they present a deficit of in-depth mass which can be 30 meters.