Résumé Les géotextiles sont devenus aujourd'hui, pour les ingénieurs de Génie civil, des matériaux indispensables dans de multiples utilisations. Si ces premières utilisations et propriétés des géotextiles commencent à être bien connues, par contre, les caractéristiques des fibres ellesmêmes, qui constituent les matériaux élémentaires des géotextiles ainsi que leurs divers modes d'assemblage, restent des notions mal assimilées dans le monde des utilisateurs. Pourtant, ces caractéristiques des fibres et modes de liaisons déterminent, pour l'essentiel, les propriétés principales que les géotechniciens peuvent attendre des produits. Cet article, illustré de nombreux schémas et micrographies optiques et électroniques, décrit les différents types de géotextiles existant sur le marché. Les propriétés physico-chimiques des matières textiles utilisées pour la fabrication des géotextiles sont brièvement rappelées. Les procédés d'assemblage et de liaison des fibres et/ou filaments textiles sont suffisamment détaillés et illustrés pour permettre une bonne compréhension des propriétés respectives des divers types de géotextiles tissés, non-tissés, tricotés, composites.

Summary It is no longer possible in present day construction practice to design civil engineering structures without including the use of geotextiles. The initial application of geotextiles in the fields of filtration, anticontamination, drainage, reinforcement, etc. which call upon the more classical properties of these products are well known to geotechnicians. On the other hand, the knowledge users have of the characteristics of the fibres which are the basic components in these textiles, their various modes of assembly in the products, remains hazy and incomplete. However, the characteristics of fibres and the way they are assembled mainly determines the principal properties that engineers can expect of these products. Moreover, the trade identification cards which will be drafted in the future by manufacturers, following the recommendations of various national and international committees which work on these subjects, will make increasing use of specific terminology and precise technical descriptions of textiles and processes. it is therefore urgent for geotechnicians to assimilate a certain number of these concepts. This is one of the aims of this article—to describe and illustrate with numerous diagrams and optical and electronic micrographs the different types of geotextiles existing on the market. The textiles used to manufacture fibres and strands are fully described restating their mechanical and chemical characteristics. The various procedures of associating these fibres are then described, defining the following products: - woven geotextiles: products made by interlacing two or more layers of fibres whose weight per unit area ranges from50 to2,000 g/m2 with failure elongation from 5 to30% for strengths which may reach several thousand daN/m. The interlacing of strands leaves spaces of well-defined dimensions; - non-woven geotextiles: products manufactured by needling or heat bonding of layers of fibre and/or strands. Needling produces thick, flexible, permeable geotextiles, whereas heat bonded materials are rigid, thin, less permeable. The porimetry of these non-woven geotextiles is generally high with pores characterized by their continuity and tortuosity in the thickness and plane of the material; - composite geotextiles, produced by associating woven, non-woven geotextiles, strands and sheets. These are second generation products designed on flexible equipment which offers the possibility of supplying the civil engineer with perfected products, tailored to his needs. Having read this article, the geotechnician should possess the fundamentals necessary for a better understanding of the respective properties of the different geotextiles which will surely help towards more discerning selection and wider and increased use of these products.