The present invention is concerned with geotextiles and more particularly, with geotextiles for soil stabilisation.

BACKGROUND ART

Erosion is a significant problem on unvegetated land, particularly if it slopes steeply, where water runs over that land. Any significant rainfall is likely to run off the land causing rainfall and wash erosion. Particularly susceptible areas are river and creek banks and road cuttings.

It is well known that a slope which is subject to erosion can be stabilised if vegetation can be established on the slope, but vegetation will not establish itself when the top soil is being washed away periodically. A number of proposals to stabilise erosion banks using matting based on sugarcane bagasse, wood, wool or coconut fibres and including additives such as binding agents have had limited success. DISCLOSURE OF INVENTION

It is therefore an object of the invention to provide an organic geotextile which promotes soil stabilisation by protecting the soil surface from rainfall erosion, reducing surface runoff and promoting water infiltration into the soil, and enhancing establishment of desirable vegetation through favourable soil moisture and temperature.

It is a further object of the invention to provide an organic geotextile which suppresses growth of undesirable vegetation by providing a physical barrier to growth of the vegetation and sunlight blockage, promoting water infiltration and reducing runoff and evaporation.

According to one broad aspect of the invention there is provided an organic geotextile for soil stabilisation comprising a first layer of fine, intertwining fibres secured to a woven scrim constituting a second layer, said organic geotextile being adapted to be applied to an area of soil as a mat which serves to dissipate the hydraulic impact of rain drops and absorbs water whereby run off is reduced, deep infiltration of water into the soil is promoted and the soil is protected from rainfall erosion.

Preferably, the scrim is of sufficiently open weave and

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said first layer is of sufficiently low density that desirable vegetation can penetrate said organic geotextile in growing therethrough. It is particularly preferred that the overall density of the geotextile be 300 to 400 grams/metre ² and, more particularly, 360 grams/metre ² .

Alternatively, the geotextile may further comprise a third layer of fine, intertwining fibres secured to the scrim on the other side of the scrim to said first layer. Preferably the first layer, the scrim and the third layer are of sufficiently high density that vegetation cannot penetrate said organic geotextile. More particularly, the organic geotextile has a density between 600g/m ² and 700g/m ² , preferably 620g/m ² .

In a particularly preferred embodiment of the invention said first layer consists of a web of teased jute fibres and the scrim is a jute scrim. Preferably said third layer, where present, also consists of a web of teased jute fibres.

In order to prepare the preferred geotextile described above, jute fibre is teased through a web forming machine such as a "Garnet" or a "Card". The web is then "lapped" on an "apron" and the jute scrim (which iε woven in a separate operation) iε laid on the web of jute fibre. The web with the scrim laid on top iε then processed through a "needle punching machine" . This machine comprises a plurality of barbed needles which move up and down through the web of jute fibre and have the effect of re-orientating certain individual jute fibres from the horizontal plane to the vertical plane thereby mechanically bonding the fibres together and joining the scrim to the web. Thiε process is known as "felting" or needle punching. It is preferred that no bonding agent be added. The product iε then trimmed to the desired width and thickneεε and cut into the deεired length. Conveniently, the geotextile iε εold in a roll 25-30 metres long by 1.83 metreε wide and 3.0 millimetreε thick, by way of example.

The jute uεed to form the teaεed jute fibre can come from a variety of εourceε εuch aε new or recycled heεεian fabric or bagging, compreεεed baleε of jute fibre known aε "caddieε" or jute heεεian off cutε known aε "gunny cuttingε". Any of theεe may be uεed individually or in combination.

According to a further broad aεpect of the invention there

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iε provided a method of εtabilising soil comprising the steps of:-

(i) providing an organic geotextile comprising a first layer of fine, intertwining fibres εecured to a woven scrim constituting a second layer, said organic geotextile being adapted to be applied to an area of εoil aε a mat which εerves to dissipate hydraulic impact of rain drops and absorbε water; (ii) laying said organic geotextile over the soil with said first layer in contact with εoil; and, optionally, (iii)εecuring said organic geotextile in position, whereby run off is reduced, deep infiltration of water into the soil iε promoted and the εoil is protected from rainfall erosion.

According to a still further broad aspect of the invention there iε provided method of εtabilising an area of soil that iε vulnerable to eroεion and eεtablishing desirable vegetation in εaid area comprising the steps of:-

(i) providing an organic geotextile comprising a first low- density layer of fine, intertwining fibres secured to an open-weave woven scrim constituting a second layer, said organic geotextile being adapted to be applied to said area as a mat which serves to dissipate the hydraulic impact of rain dropε and absorbs water; (ii) laying said organic geotextile over said area with said first layer in contact with the soil; optionally, (iii)securing said organic geotextile in position; and (iv) allowing desirable vegetation to grow through said organic geotextile, whereby run off in said area iε reduced, deep infiltration of water into the εoil iε promoted and the soil is protected from rainfall erosion.

Preferably, the geotextile is fixed to the ground to ensure it remains in place. Pinning the geotextile at intervals to the ground also ensures that vigorous plant species such as millet do not lift the geotextile cover aε they grow thereby reducing its effectiveness as an erosion control agent. Typically, pins would be driven in every 600-700 mm on a gentle slop and every 400 mm on a steeper slope at the joins between each roll of geotextile used or at a rate so εtipulated by a εite engineer or similar. Each roll would also be pinned with one pin on a

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gentle εlope and two pins on a steeper slope in the centre of the roll at the same intervals as at the joins. At the top of a εlope to be stabiliεed the cover may be pinned in a trench which iε then filled in to hold the cover more εecurely. At the bottom of the slope the cover should be folded under the toe of the slope and secured under rocks where posεible or pinned.

The ground may be pretreated by grading, filling and aεεociated earthworkε, then provided with top soil, desired seed and fertiliεer prior to covering the ground with the geotextile cover. It would then be expected that vegetation will appear through the cover within one to two weekε if a vigorouε εpecieε such as millet is chosen. Preferably, a mixture of fast growing species such as millet and more desirable species such as couch, acacia, eucalypt, etc. is used. Tree and shrub species may be planted in seed form under the mat or, once the vegetation or grass is established, by cutting holes in the cover and planting them in those holeε.

According to yet another broad aspect of the invention there is provided method of stabiliεing εoil and preventing growth of undeεirable vegetation in the εoil comprising the steps of:-

(i) providing an organic geotextile comprising a first high density layer of fine, intertwining fibres secured to a high density woven scrim constituting a second layer and a third high density layer of fine, intertwining fibres εecured to the other εide of the scrim, said organic geotextile being adapted to be applied to an area of εoil as a mat which serveε to dissipate the hydraulic impact of rain drops and absorb water; (ii) laying said organic geotextile over the soil with either said first layer or said third layer in contact with εoil; and, optionally, (iii)εecuring said organic geotextile in position, whereby run off is reduced, deep infiltration of water into the soil iε promoted and the εoil is protected from rainfall erosion, said organic geotextile acting as a barrier to prevent growth of undesirable vegetation.

Preferably, the geotextile is nominally 6 mm thick, has an overall denεity between 600g/m ² and 700g/m ² , more preferably, of

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620g/m ² and is t ^, ιs sufficiently dense that it provides a physical barrier t_- weed growth aε well as preventing sunlight reaching any weeds already growing in the vicinity of the young treeε. Competition for nutrientε and εunlight iε therefore reduced and growth of the treeε iε enhanced. The growth of trees on land susceptible to erosion further εerveε to stabilise that land but the method of enhancing the growth of young trees according to the present invention is not limited to that application and is generally applicable to gardening and horticulture. BRIEF DESCRIPTION OF DRAWINGS

In order to more fully describe the invention reference will now be made to the accompanying drawings in which:-

Figure 1 iε a schematic diagram of one illuεtrative example of a geotextile in accordance with the invention suitable for soil εtabiliεation and eεtabliεhment of deεirable vegetation, and

Figure 2 iε a schematic diagram providing a partially exploded view of one illuεtrative example of a geotextile in accordance with the present invention suitable for use as a weed barrier. BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows schematically a geotextile 10 having a bottom layer 12 which contactε the soil to be stabiliεed consisting of low density teased jute fibre and a top layer 11 of jute scrim. The jute scrim used herein is a very open weave of jute fibres. The product is nominally 3mm thick, has a density of 360g/m ² and is to be referred to through the specification as "Jutemaster FM" .

Figure 2 illuεtrates a geotextile 20 having a top layer 23 and a bottom layer 22 of teased jute fibre. Each of the layers is attached to the middle layer 21 which is a jute scrim, although layer 23 is shown spaced from the scrim so that the location of the scrim can be seen. The product iε nominally 6 mm thick, has a density of 620g/m ² and is to be referred to throughout the specification as "Jutemaεter TM" .

Eyam leε

Exam le 1

(a) Materialε

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Jutemaster FM and Jutemaster TM were subject to a rainfall simulator evaluation using a soil which has been shown to be highly erodible. It is hard setting sand loam about 10cm deep, overlying a dense clay which becomes increaεingly εodic with depth. It haε the following phyεical and chemical characteriεticε.

Soil type: sodic red brown earth

Clay content: 26%

Silt content: 14%

Sand content: 60% pH: 7.1

Cation Exchange Capacity (CEC): 16 meg/lOOg

(b) Rainfall

Simulated rainfall using a rotating disc rainfall εimulator was applied for 30 minutes at 65 mm/h and 15 minutes at 130 mm/h. The high intensities were chosen to highlight the effectiveness of the geotextile against typical short, heavy storm in northern Australia. The occurrence of 30 minutes of rain at 65 mm/h would be an annual event in most partε of Queenεland. The 130 mm/h rain represents exceptional but not unusual storms in the tropicε.

The total rainfall for the low and high intenεitieε were 16.3 and 32.5 mm reεpectively.

(c) Slope Gradient

Three gradientε were tested: 3:1, 4:1 and 10:1. These gradients cover the range of εlopeε often requiring geotextile materialε for εtabiliεation.

(d) Sample Preparation

After removing large rocks and foreign materials, the soil was firmly packed into galvaniεed εteel boxes (250 mm wide, 450 mm long and 75 mm deep). The soil surface was covered completely by either Jutemaεter FM or TM.

The boxes were filled with special spoutε to collect runoff water and were tilted to the required gradientε on a stand. For each simulator run, two boxes were used.

(e) Replication

Each treatment (geotextile grade X gradient) was replicated twice.

(f) Data Collection

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For each run the following data were collected: Runoff rate Total runoff Total soil movement

Depth of wetting at 30 cm from the collecting εpout From these results, water infiltration rate, total infiltration and rainfall before runoff were calculated, (g) Results on water runoff and soil moisture testε (i) Surface runoff:

Following rain the amount of water that cannot be absorbed by the soil will run off, the runoff quantity depends greatly on the surface cover, soil roughness and land slopes. Results from Table 1 clearly show that both Jutemaster FM and TM reduce runoff greatly, particularly under high rainfall intensity.

Under low rainfall intensity conditions, where minimum runoff would be expected on bare soil surface, runoff was reduced by more than 50% under Jutemaster FM and up to 80% under Jutemaεter TM on all εlope gradientε.

The effectiveneεs of both grades was best demonstrated under high rainfall conditions. The average reduction of runoff was up to 90%. These results clearly demonstrate the suitability of Jutemaster FM for steep slope stabilisation.

The uniformity of the resultε between replications indicates that the variation in mat density is minimal and quality control iε satisfactory. Table 1: Runoff as a percentage of total rain.

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(ii) Water Infiltration:

Water infiltration into the soil depends greatly on the soil surface cover which protects the roughnesε of soil surface (soil surface structure) and also to slow down the movement of water thus enhancing the water entry/absorption to the soil.

Results shown in Table 2 demonstrate the effectiveness of both Jutemaster FM and TM in improving water infiltration to the soil. Almost total absorption was recorded under both low and high rainfall intensitieε and at all three gradientε for both gradeε. This can be explained by the fact that surface εoil εtructure under Jutemaεter remained almoεt intact after 30 minuteε of rain while the bare εoil εurface εtructure was completely destroyed. Table 2: Water infiltration as a percentage of rainfall.

(iii) Time before runoff occurred:

The results preεented above can be beεt seen in terms of the time elapsed before runoff occurred. Table 3 shows that under low intensity rainfall (65 mm/h) runoff occurred approximately 13 minuteε after rain on bare εoil on all εlope gradientε. Under high rainfall intenεity (130 mm/h) runoff occurred only 7 minuteε after rain.

However, when εoilε εurface waε protected by either Jutemaεter FM or TM, no runoff occurred at the end of the experimental periods (30 for low intenεity and 15 minutes for high intensity rainfall). Both soil erosion and soil moisture levels are inversely related to runoff quantity

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and rate. Theεe reεultε further indicate the εuitability of both gradeε of Jutemaεter in soil erosion control. Table 3: Time (minutes) before runoff occurred.

15+ and 30+ indicating no runo f occurre at t e en o experimental periodε of 15 and 30 minutes respectively.

(iv) Depth of wetting:

Soil protected by both Jutemaster FM and TM were almost completely saturated with water under both rainfall intensities and all three gradients. These are in sharp contrast with the bare soil where only up to two thirdε of the soil profile were wet (Table 4).

Table 4: Wetting depth (cm), 30 cm from the collection spouts.

75+ Comp ete y saturate .

(h) Resultε on εoil loεε

Reεultε on Table 5 clearly εhow that both Jutemaεter FM and TM were highly effective againεt εoil eroεion. When soil surface was bare, soil losseε increased as slope gradient

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increased particularly under high rainfall intensity. When the surface waε protected by either FM or TM gradeε, εoil loεεes were virtually stopped even under high rainfall intensity.

These resultε indicate that for general εlope εtabiliεation Jutemaεter FM iε an extremely effective geotextile in εoil erosion control.

Table 5: Soil concentration in runoff water (g/1) .

Example 2

A heavily eroded creek bank waε rehabilitated using Jutemaster FM in the following manner. SLOPE PREPARATION

4.1 Day One (i) All protruding edges along the bank were smoothed by the Case 350 Drott.

(ϋ) An impervious barrier of heavy black plastic (concrete liner) was pinned up againεt the embankment 0.5 - 1 metre above the existing bed level and approximately 2 metres on the gully bed. It waε pinned against the embankment to help potential piping.

(iii) 72 tonnes (6 truck loads) of various sizes of quarry face spoor were brought in and were εpread on the gully bed to give protection from gully flow. The optimum εize for the bed rockε iε 200-400 mm. j SUBSTITUTE SHEET

4 . 2 Day Two ( i ) The embankment was graded by the

Drott and major depressions were filled.

(ϋ) Agricultural gypsum was εpread manually at a rate of 0.5 - 1 kg per square metre.

(iϋ) Top soil, was spread on the embankment to a depth of 20-30 cm and compacted to 10 cm.

4 .2 Day Three ( i ) The embankment was lightly raked and then seeded with a mixture of Green Couch and Giant Bermuda Couch. Native seed of Tallowwood, Matt Rush and Black Wattle were broadcast separately. Fertiliser was broadcast over the side.

5.0 INSTALLATION (i) The Jutemaster FM was rolled from the top of the slope to the bottom with each roll overlapping 10 cm, and leaving an extra metre at the toe. It was laid looεely enough to conform to contourε and firmly enough to prevent εoil movement and bagging.

(ϋ) A trench approximately 10 - 15 cm was dug at the top of the slope with the Jutemaster being pinned in the trench and then the trench backfilled. This ensures that Jutemaster is well secured, aε when wet it becomeε very heavy.

(iϋ) Anchor pinε were driven in along the joins. Each roll was then pinned in the centre. The Jutemaster was folded under the toe of the εlope and placed under rocks where

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poεεible or pinned.

6.0 DEVELOPMENT OF VEGETATIVE COVER

6.1 Day Four

The entire slope waε thoroughly watered, making sure the moisture penetrated the top 20mm of soil. Follow-up εprinkling waε required. Within one week the millet appeared through the Jutemaster.

6.2 Progresε of Vegetative Cover.

The couch graεε did not appear to be germinating evenly, so the millet was cut to a height of 40 mm and then lightly raked to allow for greater light penetration.

By 6 weeks the millet had been brushcut twice, but seed heads started appearing. Theεe were completely removed by bruεhcutting.

The Acacia εeed εtarted germinating after 7 weeks.

Holes were cut in the Jutemaster and local tree and shrub εpecieε were planted. By thiε time the graεεes were sufficiently established to hold the Jutemaεter in place, stabilising the bank.

Variations and modifications apparent to those skilled in the art may be made without departing from the broad ambit and scope of the invention as defined in the appended claims.

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