A GEOGRID COMPOSED OF FIBER-REINFORCED POLYMERIC STRIP AND METHOD FOR PRODUCING THE SAME

'woven' so that the longitudinal and lateral polymer strips 1 and 2 are alternatively crossed up and

down as shown in FIG. 1. At this time, a ridge of the longitudinal polymer stop 1 is crossed with

the lateral polymer stop 2 to form a first contact point Q, while a valley of the longitudinal polymer

ship 1 is crossed with the lateral polymer strip 2 to fonri a second contact point C₂. According to the present invention, it is possible to produce a geogrid with various woven

structures by changing positions of the bending members 80 and 90 of the upper and lower plates

51 and 52. FIGs. 10a to lOd show examples of such a geogrid.

As shown in FIG. 10a, if two first bending members 80' are successively positioned

between the second bending members 90' along the longitudinal direction on the opposite surfaces

of the upper and lower plates 51 ' and 52', the longitudinal and lateral polymer stops are arranged

so that two second contact points C₂ are positioned between the first contact points d as shown in

FIG. 10b. hi other words, in this case, it may be understood that two lateral polymer stops are

inserted into one valley (or, one ridge) of the longitudinal polymer stop. i addition, if three first bending members 80" are successively positioned between the

second bending members 90" on the opposite surfaces of tire upper and lower plates 51" and 52" as

shown in FIG. 10c, one longitudinal polymer stop 1 has three second contact points C₂ between the

first contact points Q as shown in FIG. lOd. That is to say, tiiis may be understood that three

lateral polymer stops are inserted into one valley (or, one ridge) of the longitudinal polymer stop.

Though it is described in this embodiment regarding a n* longitudinal polymer strip and an

adjacent n+1* longitudinal polymer stop, the same principle may be applied to other longitudinal

23 polymer strips which are not adjacent to each other.

The longitudinal and lateral polymer stops 1 and 2 arranged as mentioned above are then

transferred to the welding unit 60 so that the contact points and C₂ are welded. First the upper

and lower jigs 63 and 64 shown in FIG. 7a approaches each other at the first welder 61 a to press the

polymer stop array inteiposed between the jigs 63 and 64. At this time, the first holders 63a and

64a formed on the opposite surfaces of the upper and lower jigs 63 and 64 press and support the

first contact points Q of the polymer strip array. More specifically, the support 63a of the upper

jig 63 is contacted with the upper surface of the longitudinal polymer strip 1, while the support

holder 64a of the lower jig 64 is contacted with the lower surface of the lateral polymer stop 2. At

this time, the ends of the support holders 63a and 64a have rough surfaces so as to be contacted

with the surfaces of the polymer strip without sliding.

In this state, if the upper jig 63 is vibrated in a direction perpendicular to the length of the

longitudinal polymer stop 1, for example right and left directions, with the lower jig 64 being fixed,

the polymer resin 110 of the stop is melt and the first contact points become adhered (step S340).

At this time, the vibration preferably has the frequency of 60 to 300 Hz and the amplitude of 0.3 to

1.8 mm so that the polymer resin is melt for a short time without damaging the reinforcing fiber

100 in the polymer resin.

If the first contact points are adhered as mentioned above, the longitudinal and lateral

polymer strip array is transferred again to the second welder 62 for vibration welding of the second

contact points C₂ (step S350). In the second welder 62, the second support holders 65a and 66a of the upper and lower

jigs 65 and 66 are contacted with the second contact points C₂ of the longitudinal and lateral

polymer strip array. At this time, in tiiis embodiment the support holder 65a is contacted with the

upper surface of the lateral polymer stop 2, while the support holder 66a is contacted with the lower

surface of the longitudinal polymer stop 1.

In this state, the upper jig 65 is fixed and the lower jig 66 is vibrated in a direction

perpendicular to the length of the longitudinal stop 1, for example right and left directions, so as to

perform the adhesion in the same way as the former procedure.

Though it is illustrated in the description and drawings that the first contact points and

the second contact points C₂ are separately vibration-welded, it should be understood that the

present invention is not limited to that case but various modifications may be applied thereto. For

example, the first contact points C_\ and the second contact points C₂ may be adhered using only

one welder. In this case, the first contact points is firstly adhered and then the strip array is

wound around the winder, and then the strip array is again released into the welder. At this time,

if the array is turned over for inversion of the upper and lower surfaces, the second contact points C₂ may be adhered. Furthermore, the contact points of the polymer stop may be adhered using

the ultrasonic fiictional welding or the heating, or hot-melt instead of the vibration welding.

After completing the adhesion, the geogrid is wound around the winder 71 by a regular length through the pulling unit 70. Preferably, the fiber-reinforced geogrid product has a length of 25 to 200 m for the convenience of treatment on the working spot.

25 Though the making process of the fiber-reinforced polymer stop and the producing

process of the geogrid are separately described in this embodiment these processes may be

perfonrted successively.

Hereinafter, preferred embodiments of the present invention will be described in detail.

Prior to the description, it should be understood that the embodiments according to the present

invention may be changed in various ways, and the present invention should not be interpreted to

be limited to the following embodiments. The embodiments of the present invention are intended

just for giving better perfect explanation to those ordinary skilled in the art.

The properties of the geogrid according to the embodiments are measured using the

following tests.

Wide-width Tensile Shength Test: ASTM D 4595

A sample having a width of 20 cm is fixed between clamps attached on and below the

transformation-controlling tensile strength tester and then tensioned at a rate of 10 + 3%/min, and

then tensile shength and tensile elongation are measured at the breaking point due to tensile

transformation. In case a glass fiber is used as a reinforcing fiber, the tensile strength (LASE 2%)

when the tensile strain is 2% is separately recorded, while, in case a polyester high-strength fiber is

used as a reinforcing fiber, the tensile shength (LASE 5%) when the tensile strain is 5% is

separately recorded.

26 Creep Test: ASTM D 5262

The creep test evaluates deformation behavior of the geogrid when a constant tensile load

is applied continuously at a constant temperature condition of 21 + 2°C so as to determine a tensile

strength reduction factor due to the creep, which is considered in design. In tiiis experiment 45%

load of the maximum tensile shengtli of the geogiid sample is applied to the sample, and the creep

strain is measured after 1 ,000 hours.

Assessment of Installation Damage: ASTM D 5818

A base subgrade is treated in the same way as the actual structure building, then a geogrid

sample of at least 10 m² is installed, a fill material is installed thereon, and then they are compacted

in the same way as the actual structure building. As for the fill material, aggregate having a size of

at most 20 mm is compacted in a thickness of 30 cm, and then the geogrid sample is installed and

the same fill material is installed again thereon in a thickness of 30 cm, and then a vibration roller of

lOton capacity is used for four time reciprocating compaction. After the compaction, the compacted aggregation is removed not to damage the geogrid so

that the geogrid sample is exhumed, and then a tensile shength is tested for the exhumed sample to

calculate a shength reduction rate in comparison to the tensile strength of the original sample.

Test for Shape Stability Installation and compaction are conducted in the same way as the assessment of

27 installation damage, and then contact points of the longitudinal and lateral stops are observed. If

the number of separated contact points is more than 20%, it is evaluated as "inferior", if the number

of separated contact points is in the range of 10 to 20%, it is evaluated as "norrnaT, while hie

number of separated contact points is less than 10%, it is evaluated as "superior".

Evaluation of Pullout Test

Soil is filled in a soil box having a length of 140 cm, a width of 60 cm, and a height of 60

cm, and the geogrid is installed in the soil. At this time, the geogrid sample is connected to a

drawing device through a slit of 2.5 cm. In addition, a rubber membrane is mounted to the upper

portion of the soil box so as to apply a uniform vertical load to the soil box by means of air pressure.

Then, with changing the vertical load from 0.3 to 1.2 kg/cm² (3 to 12 kN/cm²), an interaction

coefficient Q showing a fiictional force between the geogrid and the soil is evaluated by analyzing

the pullout displacement of the geogrid at the maximum pullout force, with a pullout displacement

rate of 0.1 cm/min.

Embodiment 1

A polyester liigh-tenacity fiber bundle of 48000 deniers is passed through a nipple having a

rectangular section and through a rectangular die to make a longitudinal fiber-reinforced polymer

strip having a section shown in (a) of FIG. 1 la with a width of 8.4 mm and a thickness of 2.3 mm.

In addition, a lateral fiber-reinforced polymer stop having the same section as the longitudinal

28 fiber-reinforced polymer stop with a width of 6.3 mm and a thickness of 1.5 mm is made with the

use of polyester high-tenacity fiber bundle of 20000 deniers. Polypropylene having a melt index

of 4 is used as a themioplastic polymer resin. Then, the longitudinal fiber-reinforced polymer

stops are arranged on the strip airanging unit so that a product width is 4 m and a distance between

the stops is 40 mm, and then the lateral fiber-reinforced polymer stops are inserted at an interval of

50 mm to have an angle of 90° with the longitudinal stop, thereby making a lattice having a plain

weave structure as shown in FIG. 1. Subsequently, the first welder welds contact points at which

the longitudinal stop is positioned above the lateral stop, by vibrations having a frequency of 194

Hz and an amplitude of 0.5 mm. And then, the lattice is moved to the second welder so as to weld

contact points at which the longitudinal stop is positioned below the lateral stop, by vibration

having a frequency of 194 Hz and an amplitude of 0.5 mm, thereby making a geogrid. The

number of ribs per unit length (ribs/m), a wide- width tensile strength (kN/m), LASE5% (kN/m), a

tensile strain (%), a creep strain (%) and a shength reduction rate (%) under construction of the

produced geogrid are shown in the following table 1, and an interactive coefficient in pullout and

shape stability are shown in the following table 4.

Embodiment 2

Two polyester high-tenacity fiber bundles of 24000 deniers are passed through a two-hole

nipple having a rectangular section and through a rectangular die to make a longitudinal

fiber-reinforced polymer stop having a section shown in (b) of FIG. 1 la with a width of 8.4 mm

29 and a tiiickness of 2.3 mm. hi addition, a lateral fiber-reinforced polymer ship having the same

section as the longitudinal fiber-reinforced polymer stop with a width of 6.3 mm and a tiiickness of

1.5 mm is made with the use of two polyester high-tenacity fiber bundles of 10000 deniers. Then,

the stops are arranged in the same way as the first embodiment to produce a geogiid. The number

of ribs per unit lengtli (ribs/m), a wide-width tensile strength (kN/m), LASE5% (kN/m). a tensile

strain (%), a creep strain (%) and a shength reduction rate (%) under construction of the produced

geogrid are shown in the following table 1.

Embodiment 3 Three polyester high- tenacity fiber bundles of 16000 deniers are passed through a

three-hole nipple having a rectangular section and through a rectangular die to make a longitodinal

fiber-reinforced polymer strip having a section shown in (c) of FIG. 11a with a width of 8.4 mm

and a thickness of 2.3 mm. In addition, a lateral fiber-reinforced polymer stop having the same

section as the longitudinal fiber-reinforced polymer strip with a width of 6.3 mm and a thickness of

1.5 mm is made with the use of four polyester high-tenacity fiber bundles of 5000 deniers. Then,

the stops are arranged in the same way as the fust embodiment to produce a geogrid. The number

of ribs per unit lengtli (ribs/m), a wide-width tensile strength (kN/m), LASE5% (kN/m), a tensile

strain (%), a creep strain (%) and a shength reduction rate (%) under construction of the produced

geogrid are shown in the following table 1.

30 Embodiment 4

Eight polyester high-tenacity fiber bundles of 3000 deniers are passed through a four-hole

nipple having a rectangular section and through a rectangular die to make a longitudinal

fiber-reinforced polymer ship having a section shown in (e) of FIG. 11a with a width of 6.3 mm

and a thickness of 1.5 mm. In addition, a lateral fiber-rehiforced polymer stop having the same

section as the longitudinal fiber-reinforced polymer strip with a width of 6.3 mm and a thickness of

1.5 mm is made with the use of four polyester high-tenacity fiber bundles of 5000 deniers. Then,

the stops are arranged in the same way as the first embodiment to produce a geogrid. The number

of ribs per unit length (ribs/m), a wide-width tensile strength (kN/m), LASE5% (kN/m), a tensile

strain (%), a creep shain (%) and a strength reduction rate (%) under construction of the produced

geogrid are shown in the following table 1.

Embodiment 5

Twelve polyester high-tenacity fiber bundles of 3000 deniers are passed through a

four-hole nipple having a rectangular sechon and through a rectangular die to make a longitudmal

fiber-reinforced polymer stop having a section shown in (e) of FIG. 11a with a width of 6.8 mm

and a tiiickness of 2.0 mm. In addition, a lateral fiber-reinforced polymer ship having the same

section as the longitudinal fiber-reinforced polymer stop with a width of 6.3 mm and a thickness of

1.5 mm is made with the use of four polyester high-tenacity fiber bundles of 5000 deniers. Then,

the stops are arranged in the same way as the first embodiment to produce a geogrid. The number

31 of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m), LASE5% (kN/m), a tensile

shain (%), a creep strain (%) and a strength reduction rate (%) under construction of the produced

geogrid are shown in the following table 1.

Embodiment 6

Two polyester high-tenacity fiber bundles of 40000 deniers are passed through a two-hole

nipple having a rectangular section and through a rectangular die to make a longitudinal

fiber-reinforced polymer stop having a section shown in (b) of FIG. 1 la with a width of 11.5 mm

and a thickness of 2.5 mm. At this time, polypropylene having a melt index of 4 is used as a

themioplastic polymer resin. A lateral fiber-reinforced polymer ship having a section shown in

(c) of FIG. 1 la with a width of 6.3 mm and a thickness of 1.5 mm is made with the use of three

polyester high-tenacity fiber bundles of 7000 deniers and a three-hole nipple having a rectangular

section. A position of the bending members 80' and 90' of the stop arranging unit is changed as

shown in FIG. 10a, the made longitudinal stops are arranged on the stop arranging unit at intervals

of 40 mm, and then the lateral fiber-reinforced stops are inserted at intervals of 50 mm to have an

angle of 90° with the longitudinal ship, thereby making a lattice having a modified stop array as

shown in FIG. 10b. Subsequently, contact points formed in the stop array are adhered with the

use of a vibration welding device giving a frequency of 194 Hz and an amplitude of 0.5 mm to

produce a geogrid. The number of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m),

32 LASE5% (kN/m), a tensile strain (%), a creep shain (%) and a strength reduction rate (%) under construction of the produced geogrid are shown in the following table 1.

Embodiment 7

A geogiid is produced in the same way as the sixth embodiment except that a position of the bending members 80' and 90' is changed as shown in FIG. 10c.

The number of ribs per unit length (ribs/m), a wide-width tensile shengtli (kN/m), LASE5% (kN/m), a tensile shain (%), a creep strain (%) and a strength reduction rate (%) under construction of the produced geogrid are shown in the following table 1.

Table 1

Embodiment 8

A geogrid is produced in the same way as the third embodiment except that three glass fiber bundles of 2200 tex are used as a reinforcing fiber instead of polyester fiber.

The number of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m), LASE2% (kN/m) and a tensile strain (%) of the produced geogrid are shown in the following table

2.

Embodiment 9

A geogrid is produced in the same way as the sixth embodiment except that six glass fiber bundles of 2200 tex are used as a reinforcing fiber for a longitudinal ship and three glass fiber bundles of 2200 tex are used as a reinforcing fiber for a lateral strip.

The number of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m), LASE2% (kN/m), a tensile strain (%), a creep shain (%) and a shength reduction rate (%) of the produced geogrid are shown in the following table 2.

Embodiment 10

A geogrid is produced in the same way as the seventh embodiment except that six glass fiber bundles of 2200 tex are used as a reinforcing fiber for a longitudinal stop and three glass fiber

34 bundles of 2200 tex are used as a reinforcing fiber for a lateral stop.

The number of ribs per unit length (ribs/m), a wide-width tensile strength (kN/m), LASE2% (kN/m) and a tensile shain (%) of the produced geogrid are shown in the following table

Table 2

Comparative Example 1

Polyester high-tenacity fiber bundles are woven into a lattice shape, and then coated with polyvhiylchloride resin to produce a textile geogrid.

The number of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m), LASE5% (kN/m), a tensile strain (%), a creep strain (%) and a strength reduction rate (%) of the produced geogrid are shown in the following table 3.

35 Comparative Example 2

A plastic geogrid is produced according to a conventional method which is extruding a sheet with the use of polyolefin resin and then perforating and drawing the sheet on one axis.

The number of ribs per unit length (ribs/m), a wide-width tensile shength (kN/m). LASE5% (kN/m), a tensile shain (%), a creep strain (%) and a strength reduction rate (%) of the produced geogrid are shown hi the following table 3.

Comparative Example 3

A geogrid is produced by making longitudinal and lateral fiber-reinforced stops in the same way as the first embodiment. However, the lateral fiber-reinforced stops are extruded and inserted while the longitudinal fiber-reinforced stops are moving, and then the longitudinal and lateral fiber-reinforced strips are adhered with compression rollers to produce a fiber-reinforced geogrid having a lattice shape as shown in FIG. 12 with a width of 4 m.

The number of ribs per unit length (ribs/m), a wide-width tensile strength (kN/m), LASE5% (kN/m), a tensile shain (%), a creep strain (%) and a shength reduction rate (%) of the produced geogrid are shown in the following table 3, and shape stability and interactive coefficient are shown in FIG.4.

Table 3

36

Table 4

When properties of the geogrids according to the embodiments and the comparative examples 1 and 2 are compared with reference to Tables 1 to 3, the following differences will be found.

First the geogrids of the embodiments and the geogrid of the comparative example 1 show similar values in the wide-width tensile strength (kN/m), LASE5% (kN/m), the tensile strain (%) and the creep strain (%), but the shengtli reduction rate (%) is larger in the textile geogrid of the comparative example 1 rather than the geogrids of the embodiments. The strength reduction rate (%) makes it possible to estimate the installation damage, and high shength reduction rate means poor resistance to installation damage. Thus, it will be understood that the geogrids according to

37 the embodiments of the present invention shows excellent resistance to installation damage rather

than the textile geogrid. It means that the geogrid of the present invention is usable in a soil

having many rocks since the reinforcing fiber of the geogrid is protected by the polymer resin and

any damage applied in construction may be prevented. Second, the geogrids of the embodiments and the plastic geogrid of the comparative

example 2 show similar values hi the wide-width tensile shength (kN/m), LASE5% (kN/m) and

the strength reduction rate (%), but they show some difference in the tensile shain (%) and the

creep strain (%). In particular, the creep shain (%) of the comparative example 2 is three times of

that of the embodiments. This shows that the plastic geogrid has lower resistance against the

creep deformation rather than the geogrid of the present invention. That is to say, the

conventional plastic geogrid shows high creep strain due to insufficient drawing at its junction

points of longitudmal and lateral ribs when a load is applied thereto for a long time, while the

geogrid of the present invention greatly improves resistance against the creep deformation since it

is reinforced with the fiber having good resistance against the creep deformation. hi addition, if the properties of the geogrids of the embodiments are compared with those

of the comparative example 3, the following differences are revealed.

First though the shength reduction rate is similar in both cases, the shape stability is very

different. That is to say, the geogrid of the comparative example 3 is apt to easily separate its

contact points by a vertical load (see FIG. 13b), while, in the geogrid of the present invention, only

the contact points adhered below a lateral stop are separated due to the specific structure in which

38 the longitudinal and lateral fiber-reinforced polymer stops are arranged up and down in turns (see

FIG. 13a).

Second, after the interaction coefficients between the soil and the reinforcing material

are compared, it is found that the interaction coefficient of the geogrid of the first embodiment is

0.95 and the interaction coefficient of the geogiid of the comparative example 3 is 0.88. That is

to say, the interactive coefficient of the geogrid according to the first embodiment is higher than that

of the geogrid according to the comparative example 3. In connection with this fact the

interaction coefficient is influenced by the shape of the geogrid, particularly by the shape of

members positioned vertical to a pullout direction, hi the experiment for the geogrid having the

same width of 60 cm, the geogrid of the comparative example 3 is configured so that the stop

positioned vertical to a pullout force has a length of 60 cm, but the geogrid of the first embodiment

is configured so that trie ship positioned vertical to a drawing force has a lengtli of more than 60 cm

since a curvature is generated in the stop due to the up/down alternative arrangement. Thus, the

passive resistant member of the geogrid according to the present invention gives larger contact area

with the soil than that of the comparative example 3, so the geogrid of the present invention may

give more excellent reinforcing function.

INDUSTRIAL APPLICABILITY

As mentioned above, since the longitudinal and lateral fiber-reinforced polymer stops are

alternatively arranged up and down and their cross contact points are welded and fixed to increase

39 resistance against vertical load and frictioiial force with a reinforced material such as soil, the

geogrid of the present invention gives excellent shape stability and superior resistance to installation

damage. In addition, since the geogiid of the present invention uses the fiber-reinforced polymer

strip in which a fiber is reinforced in a polymer resin, the geogiid of the present invention shows

high tensile strength, low tensile strain and low creep shain. Thus, the geogrid of the present

invention may be useful as a reinforcing material in various civil engineering works such as for

retailing wall reinforcement slope reinforcement or soft ground reinforcement and as a protecting

net of a building or other installations.

In addition, by using the method for producing a geogrid according to the present invention,

it is possible to mass-produce the geogrids at a low cost.

The present invention has been described in detail. However, it should be understood that

the detailed description and specific examples, while indicating preferred embodiments of the

invention, are given by way of illustration only, since various changes and modifications within the

spirit and scope of the invention will become apparent to those skilled in the art from this detailed

description.

40