Indian Journal of Fibre & Textile Research Vol. 33, September 2008, pp. 339-344 Designer natural fibre geotextiles—A new concept Subhash Anand a Centre for Materials Research and Innovation, The University of Bolton, Bolton, U.K. This paper reports the development in flat weft knitting technology; the design and production of the novel natural fibre geotextiles along with their interactive behaviour in different soil types and conditions. These natural fibre products are found to be much more environment-friendly than their synthetic equivalents; the fibres themselves are a renewable resource and are biodegradable. Such structures would also offer economical benefits to a number of developing countries, where vegetable fibres are grown and cultivated in large quantity. These structures have been designed to provide the highest possible strength in one direction , combined with the ease of handling and laying on site; soil particles interlock with the fabric to such an extent that the soil/fabric interface exhibits greater shearing resistance than the surrounding soil, i.e. the soil/fabric coefficient of interaction is greater than one; a degree of protection to the high strength yarns during installation; a tensile strength in the range of 100-200 kN m -1 ; and ease of manufacture on conventional textile machines. Keywords: Flat weft knitting technology, Geotextile, Knitted fabric, Nonwovens, Soil reinforcement 1 Introduction Geotextiles are used in numerous civil engineering applications for reinforcement, filtration, separation, drainage and erosion control. Mainly, there are four types of polymers used as raw materials, viz. polyester, polyamide, polypropylene and polyethylene. They can be woven, nonwoven, knitted, knotted, grids, membranes and even composite materials. They represent one of the fastest growing markets of all technical textiles. In a recent document entitled “A competitiveness analysis of the UK technical textiles sector” commissioned by the DTI, UK, amongst the areas highlighted as having above average growth potential over the next decade especially within the UK and wider European markets, the nonwoven and woven geotextiles show 5.9% and 5% growth per annum in value terms respectively. 1 In many ground engineering situations, e.g. temporary roads over soft land, basal embankment reinforcement, geotextiles are only required to function for a limited time period. Furthermore, synthetic geotextiles are normally prohibitively expensive for developing countries. Many of these countries have abundant supplies of cheap, indigenous natural fibres (jute, sisal, coir, etc) and textile industries capable of converting them into geotextile fabrics. This paper reports the development in flat weft knitting technology; the design and production of the novel natural fibre geotextiles along with their interactive behaviour in different soil types and conditions. 2 Properties Required in Geotextiles As stated earlier that the goetextiles can perform several functions either individually or simultaneously, this versatility relies upon their structural, physical, mechanical and hydraulic properties. The emphasis of the use of geotextiles in this paper is on short-term reinforcing applications. The general properties required to perform this function are given in Table 1 ____________________________ a To whom all the correspondence should be addressed. E-mail: [email protected]Table 1Functional requirements for reinforcing geotextiles 2 Properties Requirement status Properties Requirement status Tensile strength HI Creep HI Elongation HI Permeability NA-MI Chemical resistance I-HI Resistance to flow MI Biodegradability HI Properties of soil HI Flexibility MI Water HI Friction properties HI Burial HI Interlock HI UV light I Tear resistance MI Climate NA Penetration MI QA & control HI Puncture resistance MI Costs HI HI – Highly important, I – Important, MI – Moderately important, NA – Not applicable.
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Indian Journal of Fibre & Textile Research
Vol. 33, September 2008, pp. 339-344
Designer natural fibre geotextiles—A new concept
Subhash Ananda
Centre for Materials Research and Innovation, The University of Bolton, Bolton, U.K.
This paper reports the development in flat weft knitting technology; the design and production of the novel natural fibre
geotextiles along with their interactive behaviour in different soil types and conditions. These natural fibre products are
found to be much more environment-friendly than their synthetic equivalents; the fibres themselves are a renewable resource
and are biodegradable. Such structures would also offer economical benefits to a number of developing countries, where
vegetable fibres are grown and cultivated in large quantity. These structures have been designed to provide the highest
possible strength in one direction , combined with the ease of handling and laying on site; soil particles interlock with the
fabric to such an extent that the soil/fabric interface exhibits greater shearing resistance than the surrounding soil, i.e. the
soil/fabric coefficient of interaction is greater than one; a degree of protection to the high strength yarns during installation;
a tensile strength in the range of 100-200 kN m-1; and ease of manufacture on conventional textile machines.
Fig. 3—High strength yarns in the (a) length and (b) width
directions
ANAND : DESIGNER NATURAL FIBRE GEOTEXTILES
341
novelty of this invention is that the tubular natural fibre
structures of any desired width can also be produced on
these machines, which can be further filled with straw,
paper and any other type of material and used as a
geotextile structure, particularly in wet conditions, e.g.
to stabilize river banks or to provide a water drainage
path. Figure 6 illustrates a view of a flat weft knitting
machine as delivered before various modifications
have been carried out. It is not feasible to introduce
warp yarns into the knitted structure due to the
connecting bow which synchronizes the movement of
the cam systems placed on the two opposing inclined
needle beds, where the knitting needles are housed.
Figure 7 illustrates the top view of the modified and
redesigned machine with chain and sprocket
arrangement, which facilitates the insertion of warp
threads via tubes placed vertically across the whole
machine width (Fig. 8). A close-up view (end-view) of
the machine showing the needles in opposing needle
beds, knitting feeders and knitting yarns and thick warp
yarns introduced vertically between the two needle beds
across the entire machine width is shown in Fig. 9. The
modified knitting machine also requires a creel to house
the warp yarns as well as a modified and continuous
fabric take-up system to cope with a heavy and thick
fabric. This novel technology and associated inventions
have been protected through a patent application and are
currently being commercially exploited by a UK knitting
company.4
Figures 10 and 11 show the fabric structures with
reinforcing yarns laid-in the width direction and the
strength yarns incorporated in the warp direction are
shown in Fig. 12.
Fig. 4—Sisal/flax novel knitted geotextile with reinforcement in
the width direction
Fig. 5—Sisal/flax novel knitted geotextile in grid structure
Fig. 6—Flat weft knitted machine with a conventional bow
Fig. 7—Modified and redesigned flat weft knitted machine
without bow
Fig. 8—Warp insertion tubes
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2008
342
4 Performance Assessment In a study
5 at the University of Bolton, eleven
different geotextile fabrics with different fibre types
and/or fabric structures were systematically
investigated for a wide range of performance criteria
of geotextiles for soil reinforcement. Some properties
of all eleven types of geotextiles tested and analyzed
are presented in Table 2 (ref. 2). The list consists of
two fabrics designed and produced using the novel
knitting technique developed during this work (fabrics
1 and 2); 3 woven fabrics using vegetable fibre yarns
also produced during this study (fabrics 3-5); and
fabrics 6-11 obtained from external sources for
comparison with the vegetable fibre geotextiles. It is
observed from Table 2 that all natural fibre
geotextiles have high strength, low breaking extension
and high modulus in the strength direction. It is also
expected that these structures would also possess low
elasticity and creep values, which are essential for soil
reinforcement purposes.
4.1 Measurement of Shearing Interaction
Eleven geotextiles were tested in a 300 × 300 mm
partially fixed direct shear box. The relative
horizontal displacement of the two halves of the shear
box, the change in sample height during shearing and
the vertical displacement of the top four corners of the
upper half of the shear box were monitored by linear
dial gauges. The tests were conducted with dry
Leighton Buzzard sand and limestone gravel (average
particle diameter 0.8 mm and 6 mm respectively).
Nominal normal stresses of 50, 100, 150 and 200
kNm-2
were applied to the samples to represent the
likely range of soil pressures which would apply to
field situations.
The upper and lower halves of the shear box were
completed each in three layers of equal thickness
using a vibrating hammer and tamping plate to a
predetermined thickness to produce a normal unit
weight of 96% and 94% of the maximum nominal dry
unit weight for the sand and gravel respectively.
These figures were chosen to represent the density
likely to be achieved on site, whilst maintaining an
accuracy of ± 01 mg m-3
from the mean dry density in
subsequent shear box tests. The leading side of the
bottom half of the shear box has the geotextile
clamped to it.2
4.2 Coefficient of Interaction
The efficiency of geotextiles in developing
shearing resistance at the soil-fabric interface is
indicated by the coefficient of interaction (á) defined
Fig. 9—Warp insertion viewed from the end of machine
Fig. 10—Reinforcing yarns in width direction
Fig.11—Knitted grid construction
Fig 12—Different structures of reinforcing yarns in length
direction
ANAND : DESIGNER NATURAL FIBRE GEOTEXTILES
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INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2008
344
as the ratio of the friction coefficient between soil and fabric (tan ä) and the friction coefficient for soil sliding on soil (tan ö). Values of peak (ö’max) and residual (ö’r) shearing angles together with their coefficient of interaction (á) are shown in Table 3 (ref. 2), some of these values are above one for the
sand (e.g. in case of knotted coir geotextile), indicating that by introducing the geotextile in the sand it actually strengthens the ambient sand. This could possibly be due to the surface texture of some of these geotextiles, in that the sand grains can interlock with the fabric and reduce movement. The
main properties required for reinforcing geotextiles for short-term applications can be generalized in that they must possess high tensile strength with low breaking extension and provide a good shear resistance in the fill used for the construction works. Table 3 shows that for overall performance the
nonwoven natural fibre geotextiles (fabrics 8 and 9) are found to be the least suitable for reinforcing application. The geotextiles made with the knitted and woven vegetable fibre (fabrics 1-5) show the best performance; all of these structures having been designed and produced at the University of Bolton.
5 A
further research programme investigated other natural fibre yarns, e.g. cotton; biodegradable manufactured yarns such as staple-fibre viscose rayon and filament viscose rayon; and other novel structures such as those based on single-jersey structures and incorporating high strength yarns in the machine
direction.6 It has been demonstrated that this novel
technology could be adopted for the manufacture of natural fibre geotextiles at a reasonable cost and would provide efficient and high performance geotextiles for short-term solutions for construction and civil engineering applications.
5 Conclusions A wide range of new and novel knitted structures
have been designed and developed using a modified
and redesigned flat knitting equipment. These natural
fibre geotextiles are found to have superior properties
in comparison to the mid-range of synthetic geo-
textiles for soil reinforcement, when considering
strength and frictional resistance. The high degree of
frictional resistance of the vegetable fibre geotextiles
is probably developed from both the coarseness of the
natural fibre yarns and the novel structures. These
vegetable fibre geotextiles will be much more
environment-friendly than their synthetic counterparts
and the fibres themselves are a renewable resource
that is biodegradable.
Acknowledgement The author wishes to express his gratitude to Dr
Martin Pritchard and Professor Bob Sarsby for the
significant contributions right from the conception of
this novel invention.
References 1 Anand S C, Devlopments in technical fabrics–Part 2, Knitting
Int, August (2000)53.
2 Pritchard M, Anand S C & Sarsby R W, Novel vegetable fibre
geotextile structures for soil reinforcement, Proceedings,
Conference on Textiles Engineered for Performance, UMIST,
20-22 April 1998.
3 Pritchard M, Sarsby R W & Anand S C, Textiles in civil
engineering: Part 2–Natural fibre geotextiles, Handbook of
Technical Textiles; edited by A R Horrocks and S C Anand