Geotextiles have been used very successfully in road construction for over 30 years. Their primary function is to separate the sub base from the subgrade resulting in a stronger road construction.The geotextile performs this function by providing a dense mass of fibers at the interface of the two layers. It is suggested that the ability of a geotextile to act as a separator is largely independent of the mechanical characteristic of the geotextile and that strain softening geotextiles can still perform this role when strained past their peak values. A strain energy approach to design is not routine in geotechnical engineering design, as it is difficult to quantify the external energy supplied to the system and the internal energies of the individual components making up the construction. Recent research has suggested that an equivalence of strain energy, between different geotextile types, may exist up to the in service strain. Comparing the actual strain energy and that calculated using a simplified approach shows that significant errors are introduced by firstly ignoring the nonlinear characteristics of the stress-strain curve and secondly by not considering the entire area under the stress-strain curve to rupture of the geotextile. Based on the difficultly in using the strain energy approach in geotechnical engineering design and the significant inconsistencies that can exist in its calculation, it is suggested that the concept of.-strain energy is not an appropriate parameter for characterising geotextiles.

Introduction:

Geotextiles have proven to be among the most versatile and cost-effective ground modification materials. Their use has expanded rapidly into nearly all areas of civil, geotechnical, environmental, coastal, and hydraulic engineering. They form the major component of the field of geosynthetics, the others being geogrids, geomembranes and geocomposites. The ASTM defines geotextiles as permeable textile materials used in contact with soil, rock, earth or any other geotechnical related material as an integral part of civil engineering project, structure, or system. Based on their structure and the manufacturing technique, geotextiles may be broadly classified into woven and nonwoven. Woven geotextiles are manufactured by the interlacement of warp and weft yarns, which may be of spun, multifilament, fibrillated or of slit film. Nonwoven geotextiles are manufactured through a process of mechanical interlocking or thermal bonding of fibers/filaments.

Mechanical interlocking of the fibers/filaments is achieved through a process called "needle punching". Needle-punched nonwoven geotextiles are best suited for a wide variety of civil engineering applications and are the most widely used type of geotextile in the world. Interlocking of the fibers/filaments could also be achieved through "thermal bonding". Heat-bonded geotextiles should be used with caution, as they are not suitable for filtration applications or road stabilization applications over soft soils.

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Originally published in New Cloth Market : February 2010