Hazard susceptibility related to clay shrinkage–swelling phenomena in north-eastern Tunisia (Grombalia area)

Abstract

The investigation of the shrinkage–swelling phenomena in argillaceous formations of the Grombalia area (north-eastern Tunisia) has allowed the identification of three classes of clays. The first class contains three argillaceous formations and has a low susceptibility towards shrinkage–swelling phenomena. The second class, represented by four argillaceous formations, has an average susceptibility. The third class, comprises four argillaceous formations that have a high susceptibility. Therefore, in the study region, the hazard susceptibility towards the constructions can be significant for certain zones, because of the extension of constructions which is the result of the development of demography and industry in the recent years. Three indices have been determined to obtain these classes: the lithology indices, the mineral composition indices and the geotechnical indices. A description of the lithology of geological formations and X-ray diffraction results from analysis on bulk samples allow recognising the amount of clays in each formation. However, argillaceous formations composed essentially by clays does not mean that it has a high susceptibility towards shrinkage–swelling phenomena. To improve interpretation, XRD results reveal the volume proportion of minerals that exists in each argillaceous formation. Indeed, formations having high susceptibility towards shrinkage–swelling phenomena show a high volume of smectites and/or interstratified. The additional data provided from geotechnical study on argillaceous formations have allowed an inference about the degree of the shrinkage–swelling susceptibility for all the argillaceous formations in the Grombalia area. In fact, geotechnical results have allowed determining the plasticity index value, the methylene blue value and the linear shrinkage value. Determining the degree of the shrinkage–swelling susceptibility must be inferred from the three indices (lithology, mineralogy and geotechnical), because applying only the results of one feature can lead to a false decision.