Clay and Marl Formation Susceptibility in Mila Province,

Abstract In Mila Province, Algeria (a.k.a Mila Wilaya), sensitive clays presenting shrinkage-swell ing phenomena are widespread, covering large areas. Due to this, constructions and infrastructures sustain ability built on such soils is questionable. Such clays sensitivity is amplified by seasonal rainfall deficits which reaches extreme magnitudes. In order to develop disasters’ prevention measures, we present in this work, areas mapping susceptible to shrinkage swelling phenomenon by adopting a French method developed by B R G M. This method takes into account three measurable characteristics: i.e. lithological, mineralogical and geotechnical, of clayey formations identified in the studied sector. Based on these characteristics, three scores are attributed for each formation. Then, the susceptibility index is the obtained score average for each clayey formation. The susceptibility map is established on this index basis with three classes: low, medium, high.

Keywords Clay  Shrinkage-swelling Susceptibility  Cartography  Mineralogy  Foundation

Most the Northern Algerian territory is in quite unfavorable ‘‘Geotechnical-climate’’ conditions where the shrinkage-swelling phenomenon affects clayey formations. This is mainly due to, at least, the following reasons:

  • The seasonal rainfall deficits for which the maximum magnitudes are recorded, (Mebarki 1982). Consequently, the water content of soil varies in significant proportions and the resulting swelling that occurs on surface is maximum;
  • Clays mineralogically sensitive to these phenomena are permanently encountered, because, very often, these extreme climate changes are causing clay minerals formation which is swelling clays.

Unfortunately in Algeria, the parameters governing the shrinkage-swelling soils are not usually taken into account in geotechnical campaigns conducted for construction projects: their determination is not of common practice.

The shrinkage-swelling of some geological formations are likely to cause differential settlement that can be accompanied by disorders which mainly affect buildings and infrastructure projects. The aim of the present research is to provide useful recommendation for Algerian makers when constructer on swelling soils.

Indeed, experiments throughout the world show that when simple cost effective construction regulations are respected, most of disasters scenarios are avoided. In this view the susceptibility map in Algerian Mila Province is intended for clayey and marl formations.

Observation serial has been carried out concerning the relevant to problems caused by the development projects implementation on these lands.

It is especially focused on sites where geotechnical investigations have been performed and recorded data are available at several laboratories.

The present work considers the methodology adopted and published recently by the Bureau of Geological and Mining Research (BRGM, France). This methodology provides a qualitative susceptibility of shrinkage-swelling, based on a hierarchical classification of clay formations primarily identified from the geological map, and taking into account three quantifiable characteristics (rated from 1 to 4) namely: lithologic characterization of each formation; mineralogical characterization of the induced clay phase and the geotechnical characterization of each formation. The susceptibility index is the score average selected for each clay formation. The susceptibility map is based on this index with three levels: low, medium, high.

First the geography and the geological context of Mila Province are presented. Second, a characterization of marl and clay formations is proposed based their hierarchy, lithology mineralogy and geotechnical criteria. Then a map of shrinkage-swelling susceptibility is elaborated by the implementation of a numerical model.