GEOTEXTILES

1. INTRODUCTION

According to the historical record, it is believed that the first applications of geotextiles were woven industrial fabrics used in 1950’s. One of the earliest documented cases was a waterfront structure built inFlorida in 1958. Then, the first nonwoven geotextile was developed in 1968 by the Rhone Poulence company in France. It was a comparatively thick needle-punched polyester, which was used in dam construction in France during 1970.

In fact, the geotextile is one of the members of the geosynthetic family. Those members include the following items

1.      Geogrids

2. Geonets
3. Geotextiles
4. Geomembranes
5. Geosynthetic Clay Liners
6. Geopipe
7. Geocomposites

What is geotextile?

As we know, the prefix of geotextile, geo, means earth and the ‘textile’ means fabric. Therefore, according to the definition of ASTM 4439, the geotextile is defined as follows:

"A permeable geosynthetic comprised solely of textiles. Geotextiles are used with foundation, soil, rock, earth, or any other geotechnical engineering-related material as an integral part of human-made project, structure, or system."

The ASAE (Society for Engineering in Agricultural, Food, and Biological Systems) defines a geotextile as a "fabric or synthetic material placed between the soil and a pipe, gabion, or retaining wall: to enhance water movement and retard soil movement, and as a blanket to add reinforcement and separation." A geotextile should consist of a stable network that retains its relative structure during handling, placement, and long-term service. Other terms that are used by the industry for similar materials and applications are geotextile cloth, agricultural fabric, and geosynthetic.

2. THE TYPES OF GEOTEXTILE

In general, the vast majority of geotextiles are made from polypropylene or polyester formed into fabrics as follows:

• Woven monofilament

• Woven multifilament

• Woven slit-film monofilament

• Woven slit-film multifilament

• Nonwoven continuous filament heat bonded

• Nonwoven continuous filament needle-punched

• Nonwoven staple needle-punched

• Nonwoven resin bonded

• Other woven and nonwoven combinations

• Knitted
• 
  

• 3. RAW MATERIAL OF GEOTEXTILE

The four main polymer families most widely used as the raw material for geotextiles are:

Polyester

Polyamide

Polypropylene

Polyethylene

The oldest of these is polyethylene, which was discovered in 1931 in the research laboratories of the ICI. Another group of polymers with a long production history is the polyamide family, the first of which was discovered in 1935.The next oldest of the four main polymer families relevant to geotextile manufacture is polyester which was first announced in 1941.The most recent polymer family relevant to geotextiles to be developed was polypropylene, which was discovered in 1954. The comparative properties of these four polymer are shown in very general items in Table 1.

Table 1

	Polyester	Polyamide	Polypropylene	Polyethylene
Strength	H	M	L	L
Elastic modulus	H	M	L	L
Strain at failure	M	M	H	H
Creep	L	M	H	H
Unit weight	H	M	L	L
Cost	H	M	L	L
Resistance to:
U.V. light stabilized	H	M	H	H
unstabilized	H	M	M	L
Alkalis	L	H	H	H
Fungus, vermin	M	M	M	H
Fuel	M	M	L	L
Detergents	H	H	H	H

H: High; M: Medium; L: Low

4. THE BASIC PROPERTIES OF GEOTEXTILE[1]

The properties of polymer material are affected by its average molecular weight (MW ) and its statistical distribution. Increasing the average MW results in increasing:

• tensile strength
• elongation
• impact strength
• stress crack resistance
• heat resistance

Narrowing the molecular weight distribution results in:

• increased impact strength
• decreased stress crack resistance
• decreased processability

Increasing crystallinity results in:

• increasing stiffness or hardness
• increasing heat resistance
• increasing tensile strength
• increasing modulus
• increasing chemical resistance
• decreasing diffusive permeability
• decreasing elongation or strain at failure
• decreasing flexibility
• decreasing impact strength
• decreasing stress crack resistance

5. MARKET ACTIVITY

To say that the market activity of geosynthetics in the geotechnical, transportation, and environmental areas is strong is decidedly an understatement. To obtain an insight into the vitality of geosynthetics, note the curves in the graphs in fig 3a and 3b. The curves in Fig. 3a gives the estimated amount of geosynthetics used in North America over the years(geopipe is not shown ), while the curve in Fig 3b gives the estimated in-place expenditures of these products.

Used in the calculations were the data for 1995 (note that the values are in millions of square meters and millions of dollars ) [ 1 ]:

Geotextiles 500 Mm² @ $ 0.9 / m² = $ 450 M
Geogrids 40 Mm² @ $ 2.50 / m² = $ 100 M
Geonets 50 Mm² @ $ 2.00 / m² = $ 100 M
Geomembranes 75 Mm² @ $ 10.00 / m² = $ 750 M
Geosynthetic clay linears 50 Mm² @ $ 2.5 / m² = $ 125 M
Geocomposites 25 Mm² @ $ 5.00 / m² = $ 125 M
Geo-others 5 Mm² @ $ 4.00 / m² = $ 20 M
Total ( 1995 ) $ 1670 M

6. THE BASIC FUNCTION OF GEOTEXTILE

Geotextiles form one of the two largest groups of geosynthetics. Their rise in growth during the past fifteen years has been nothing short of awesome. They are indeed textiles in the traditional sense, but consist of synthetic fibers rather than natural ones such as cotton, wool, or silk. Thus biodegradation is not a problem. These synthetic fibers are made into a flexible, porous fabric by standard weaving machinery or are matted together in a random, or nonwoven, manner. Some are also knit. The major point is that they are porous to water flow across their manufactured plane and also within their plane, but to a widely varying degree. There are at least 80 specific applications area for geotextiles that have been developed; however, the fabric always performs at least one of five discrete functions:

1.     Separation 

Geotextiles function to prevent mutual mixing between 2 layers of soil having different particle sizes or different properties. Table 2 shows the required properties for separation:

 Table 2 The required properties for separation

	Mechanical	Hydraulic	Long-term Performance
During installation	Impact resistance Elongation at break	Apparent opening size ( A.O.S.) Thickness	UV resistance
During construction	Puncture resistance Elongation at break	Apparent opening size ( A.O.S.) Thickness	Chemical stability UV resistance
After completion of construction	Puncture resistance Tear propagation resistance Elongation at break	Apparent opening size ( A.O.S.) Thickness	Chemical stability Resistance to decay

2. Drainage :

The function of drainage is to gather water, which is not required functionally by the structure, such as rainwater or surplus water in the soil, and discharge it.

Table 3. The required properties for drainage:

	Mechanical	Hydraulic	Long-term Performance
Permanent drainage function	Influence of normal overburden pressure	Permeability Thickness Apparent opening size (A.O.S.)	Chemical properties of water and soil Chemical stability Decay resistance
Temporary drainage function	Influence of normal overburden pressure	Permeability Thickness Apparent opening size (A.O.S.)

3. Filtration :

Filtration involves the establishment of a stable interface between the drain and the surrounding soil. In all soils water flow will induce the movement of fine particles. Initially a portion of this fraction will be halted at the filter interface; some will be halted within the filter itself while the rest will pass into the drain. The geotextile provides an ideal interface for the creation of a reverse filter in the soil adjacent to the geotextile. The complex needle-punched structure of the geotextile provides for the retention of fine particles without reducing the permeability requirement of the drain.

Table 4. The required properties for Filtration:

	Mechanical filter stability	Hydraulic filter stability	Long-term performance
Permanent filter function	A.O.S. Thickness	Geotextile permeability	Chemical properties of water and soil Chemical stability Decay resistance
Temporary filter function	A.O.S. Thickness	Geotextile permeability

4. Reinforcement

Due to their high soil fabric friction coefficient and high tensile strength, heavy grades of geotextiles are used to reinforce earth structures allowing the use of local fill material.

Table 5: The required properties for reinforcement:

	Mechanical	Hydraulic	Long-term performance
Base failure	Shear strength of bonding system	Hydraulic boundary conditions	Chemical and decay resistance
Top failure	Tensile strength of geotextile Geotextile/ soil friction	Hydraulic boundary conditions	Chemical and decay resistance
Slope failure	Tensile strength of geotextile Geotextile/ soil friction		Creep of the geotextile/ soil system Chemical and decay resistance

5. Protection:

Erosion of earth embankments by wave action, currents and repeated drawdown is a constant problem requiring the use of non-erodable protection in the form of rock beaching or mattress structures. Beneath these is placed a layer of geotextile to prevent leaching of fine material. The geotextile is easily placed, even under water.

Table 6:. The required properties for protection

	Mechanical	Long-term performance
Tunnel construction	Burst pressure resistance Puncture resistance Abrasion resistance	Chemically stable: pH=2-13 Decay resistance
Landfill and reservoir geomembrane construction	Puncture resistance Burst pressure resistance Friction coefficient	Chemically stable: pH=2-13 Decay resistance
Flat roof construction	Puncture resistance	Chemical compatibility

7. APPLICATIONS

Case ( I ) : 

 Wet soil conditions in animal feeding and high-traffic live-stock handling areas cause problems for both animals and producers, as well as the environment. Ruminating animals, such as beef, dairy, and sheep, often concentrate at stream crossings, in paddock lanes, and in feedlots and barnyards. In association with animal production, there will be concentrated farm vehicular and equipment traffic. When the animal and/or equipment traffic is excessively high, the vegetation is destroyed. During and after rainy weather, the soil in these areas turns to mud, creating an unhealthy environment for optimal livestock production, poor traction for farm equipment, and potentially poor surface water quality. Once these areas dry, they may provide rough and possibly hazardous footing for the animals.

After the vegetation in these concentrated areas is destroyed, the soil is bare and subject to erosion. In addition, once wet soil that has been trampled by livestock dries, it has a greatly reduced infiltration rate, and thus a much higher potential for producing runoff of soil and manure. Both of these conditions are conducive to creating a water quality problem. However, all of the conditions summarized above cause problems for producers as they try to properly manage the many operations for a profitable livestock production system.

The use of geotextile fabric in these high-traffic livestock areas can substantially reduce the occurrence of adverse conditions (see Figure 1). The installation of geotextile fabric combined with gravel can help provide a proper surface that animals, humans, vehicles, and equipment can travel on, and can also provide an erosion control benefit.

The purpose of this publication is to help producers, landowners, and agency and industry personnel who work with producers and landowners, understand the proper application, installation, and maintenance of geotextile fabric for agricultural applications. This publication provides an overview of a demonstration project (Using Geotextile Cloth in Livestock Operations to Reduce Nutrient and Sediment Loading in the Olentangy Watershed) on the use of geotextile fabric in high-traffic livestock areas. Some of the material provided is based on cooperative agency-industry-producer experiences from twelve project sites constructed in Morrow County, Ohio, during 1994.

Case ( II ):

The leading cause of pavement and roadway failure in the U.S. is contamination of the aggregate base and the resulting loss in aggregate strength. When aggregate is placed on a subgrade, the bottom layer becomes contaminated with soil. Over time, traffic loading and vibration punches pavement base aggregate into the soil and causes silt and clay to migrate upward. On wet sites, construction traffic causes pumping of weak subgrade soils into overlying aggregate. All of these conditions decrease the effective aggregate thickness destroying the road support and reducing roadway performance and life.

CONCEPT Of Lugeon test

Lugeon test

The Lugeon test, sometimes call also Packer test, is an in-situ testing method widely used to estimate the avarage hydraulic conductivity of rock mass. The test is named after Maurice Lugeon (1933), a Swiss geologist who first formulated the test. Basically, the Lugeon test is a costant head permeability type test carried out in a isolated part of a borehole. The results provide information about hzdraulic condictivuty of the rock mass including the rock matrix and the discontinuities.

DESCRIPTION AND PROCEDURE of Lugeon test

The test is conducted in a portion of a borehole isolated by pneumatic packers. The water is injected into the isolated portion of the borehole using a slotted pipe which it self is bounded by the inflated packers. The packers can be inflated using a gas compressor on the surafce, and so they can isolate and seal that portion of  the borehole. A pressure transducer is also located in that portion to measure the pressure with a help of reading station on the surface.
First of all, a maximum test pressure (Pmax) is defined so that it does not exceed the in-situ minimum stress, thus avoiding hzdraulic fracturing. The test is carried out at five stages including increasing and decreasing pressure between zero and maximum pressure. At each stage, a constant pressure is applied for an interval of 10 miniutes while pumping water. Water pressure and flow rate are measured everz minute. The five loading and unloading stages form a pressure loop often with the following pressure intervals:

Stage	Pressure
1st	0.50 Pmax
2nd	0.75 Pmax
3rd	Pmax
4th	0.75 Pmax
5th	0.50 Pmax

Using the average values of water presure and flow rate measured at each stage, the average hydraulic conductivity of the rock mass can be determined. Following the empiricl original definition of the test, the hzdraulic conductiviy is experessed in terms of Lugeon Unit, being the conductivity required for a flow aret of 1 liter per minute per meter of the borehole interval under a constant pressure of 1 MPa. The Lugeon value for each test is therefore calculated as follows and then an average representative value is selected for the tested rock mass.
            Lugeon Value = (q / L) x (P0 / P)
 where
q - flow rate [lit/min]
L - Length of the borehole test interval [m]
P0 - reference pressure of 1 MPa [MPa]
P - Test pressure [MPa]
Considering a homogenous and isotropic condition, one Lugeon will be equal to 1.3e-7m/s. Contrary to the continuum media, the hzdraulic conductivity of the rock mass is very much influenced by the rock discontinuities. Therefore, the Lugeon value could represent not only the conductivity but also the rock jointing condition. Typical range of Lugeon values and the corresponding rock condition is indicated in th etable below [1]

Lugeon Value	Conductivity classification	Rock discontinuity condition
<1	Very low	Very tight
1-5	Low	Tight
5-15	Moderate	Few partly open
15-50	Medium	Some open
50-100	High	Many open
>100	Very high	Open closely spaced or voids