Natural geotextiles

C LAWRENCE, University of Leeds, and B COLLIER, University of Tennessee, USA 

Hemp is one fibre type used today for producing modem natural geotextile products this plant is considered native to Central Asia and was subsequently introduced into China where for over 4,500 years it was grown for a wide range of end-uses including geotechnical applications. Thus, in their various primitive forms, natural geotextiles existed for many years. 

The systematic application of geotextiles began around the late 1950s, largely with the development of synthetic fibres. Initially, woven fabrics 

This chapter describes the types of natural fibres that are used for biodegradable geotextiles, the important properties of these fibres, the process and structures of the textile forms into which they are converted, and most importantly their geotechnical end-uses. First, however, it is necessary to understand what geotextiles are, and also their primary functions. 

Fluid transmission a geotextile can be constructed to enable a liquid or a gas to flow, usually lengthways, within the plane of the fabric. A typical example is the use of a geotextile to drain excess water in soils to reduce 

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The areal weights of woven geotextiles can be from 70 g/m 2 (for lightweight synthetics) to 1400 g/m- (heavy weight natural geotextiles). 

Datye K. R. and Gore, V. N. (1994) Application of natural geotextiles and related products. Geotextiles and Geomemhranes, 13,371-388. 

Lawrence, C. A. and Collier, B. (2005), Natural Geotextiles in Biodegradable and Sustainable Fibres, Chapter 11, Ed. Blackburn, R. S., Woodhead Publishing Limited, pp. 343-365. 

The fibres used for natural geotextile products are plant or vegetable fibres, although some research and development studies have considered the use of very low grade sheep s wool and wool waste. Figure 11.1 shows a classification of well known natural fibres. However, the only ones that meet with the technical requirements, cost effectively, are the bast fibres jute, hemp, kenaf and flax (also called soft fibres because they are from the softer region of the plants), and the hard (or leaf) and fruit fibres sisal and coir. Others of the remaining fibres, e.g. wood fibres, are sometimes used as fillers within the textile structure. 

The fibres that were desaibed above as being used for natural geotextiles, are usually extracted from four varieties of the woody-stemmed herbaceous dicotyledons (i.e. the bast fibres flax, jute, hemp and kenaf), one of the monocotyledonous plants (i.e. sisal) and one of Palmaceae (palms) (i.e. coir) [13, 14]. 

Sisal (Agave sisalana) is the most important species of hard fibre and is used for natural geotextiles as well as other industrial products. It is grown in Java, Africa and Haiti and accounts for about 1.5% of the world total natural fibre production. The leaves are harvested and subjected to a decortication process in which the epidermis and pulp are scraped from the fibre whilst simultaneously being washed. The resulting fibre mass is then dried and baled. 

Figure 11.6 also illustrates how the spun yarns are employed in weaving a fabric. One set of yams would be used as a warp (i.e. giving the length of the fabric) and the other as the weft (i.e. giving the width). The mechanical action of looms is well reported in the cited literature [23, 24]. Here, we will therefore consider certain basic parameters of importance to the properties of woven natural geotextiles. 

Based on the US Erosion Control Technology Council (ECTC) Guidelines and on published studies of natural geotextiles, the tests listed in Table 11.6 are important ones used in evaluating such products. 

Sediment resulting from water run-off on steep slopes can be detrimental to the free flow of waterways most commercial natural geotextiles target this problem. One commonly accepted method for measuring the effect of a geotextile on erosion control involves a modification to the above procedure. A 1.2 m X 1.2 m specimen of the geotextile is placed on a soil slope and a measured amount of artificial rain applied to the slope. Sediment and water run-off are then collected and measured. This test is best conducted in the field where site-specific conditions, such as inherent soil type, can be considered. 

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