Note: Descriptions are shown in the official language in which they were submitted.
V~~95/1~757 ''~ CA 02497381 1994-09-15
PCT/US9411 i)d49
HIGH PROFILE GEOTEXTILE FABRICS
TECHNICAL FIELD
This invention relates generally to three-dimensional, high-profile, woven
geotextile structures and their method for use in soil retention and
stabilization and
vegetative reinforcement. More particularly, this invention relates to a
generally planar,
single-layered homogeneous fabric woven from monofilament yarns having
different heat
shrinkage characteristics. such that, when heated, the fabric forms a thick
three-
dimensional, cuspated profile. 'The monofilament yarns have a relatively high
tensile
strength and a relatively high modulus at 10 percent elongation so as to
provide a fabric
which is greater in strength and more dimensionally stable than other three-
dimensional,
woven geotextile structures. Such a geotextile fabric is suitable for use on
slopes, ditches
I S and other embankments and surfaces where erosion control, soil
stabilization and/or
vegetative reinforcement may be necessary. The homogeneous, single-component
nature
of the fabric promotes et~sier handling and minimizes failure points, while.
offering a
thick, strong and dimensionally stable product upon installation.
BACKGROUND OF THE INVENTION
Woven fabric:. having heat-shrinkable yarns incorporated therein are well
known. For example, at lc;ast three patents to B. H. Foster in the early
1950's (U.S. Pat.
Nos. 2,6~7,644, 2,635,64E~, and 2,771,661) and one to McCord in 1956 (U.S.
Pat. No.
2,757,434) use heat-shrinkable yarns along with non-heat-shrinkable yarns to
make
honeycombed, puffed and/or corrugated fabrics for use in bedding, clothing and
the like.
In addition, woven fabrics having the same or similar general cuspated profile
or "honeycomb" type weave configuration as the present invention are known in
the art
and are used as tower packing and/or as the separation medium in mist
eliminators. For
instance, Pedersen U.S. Pa,t. No. 4,002,596 relates to a fluid treating medium
through
which fluid may pass for removing particulate material from the fluid. The
material used
is comprised of at least two sets of strands interleaved together in a
paarticular
CA 02497381 1994-09-15
1 v 1... ~ ~ . , . , 1 L L . 1J v J'U a \ )- \ .
-2-
configuration to each other so that the strands extending in one direction are
generally
straight while the strand:. extending in another direction are geometrically
arranged so as
to provide a fabric having a cuspated configuration or profile. The fabric of
the present
invention is similar in profile except it may bend the strands of yarn in both
directions.
S Nevertheless, other fabrics do in fact have similar configurations or
profiles.
However, they are typically used in mist eliminators and other apparatus where
separation
medium of this type ma;y be required. At least one such fabric is available
from the
Lumite Division of Synthetic Industries of Gainesville, Georgia. Notably,
however, none
of these fabrics have ewer been used for soil retention and stabilization or
turf
reinforcement. Significantly; this is because the yarns used to make these
fabrics are not
strong enough or do not form fabrics which are thick and durable enough or
dimensionally stable enough to withstand the extremely rugged conditions
exhibited
within soil embankments and the like. In other words, these fabrics are not
high-profile
structures. A high-profile; structwe has a thickness considerably greater than
that of an
ordinary "honeycomb" woven fabric. It is this thickness in combination with
the strength
and dimensional stability of the fabric which permits the fabric to restrain
the movement
of soil or gravel filling the; space defined by the fabric on a steep slope or
embankment.
Also of major :importance to the use of fabrics in soil design and performance
are weight, strength, and modulus. It is a combination of these properties,
including
thickness, which determines whether a geotextile fabric will be suitable for
use in soil
retention and stabilization as well as turf reinforcement. Desirably, a fabric
having a
typical tensile strength of at least about 3200 x 2400 pounds per foot (warp x
fill,
respectively) as determined by the American Society for Testing and Materials'
(ASTM)
Standard Test Method D~I595 , a modulus of at least about 10000 pounds per
foot
determined by ASTM D4595 at 10 percent elongation, and a thickness of at least
about
500 mils (0.5 inches) deaermined by ASTM D 1777 is necessary to provide soil
stabilization acrd erosion control on slopes, embankments, subgrades and
veneer layers
in places such as landfills. While some mattings and other similar structures
have,
heretofore, been used to aid in soil retention or erosion control, most of
these structures
have been generally ineffective in providing true stability and reinforcement
for the soil.
In fact, most of the prior art structures have employed generally straight
yarns in at least
WO 9S/11757 ~' ' CA 02497381 1994-09-15 ~1
PCTlUS94/10449
-3-
one direction, are not heat-shrinkable, and/or have filaments which are melt-
bonded
together so as to cause failure points to exist with respect to the bonding of
the fabric.
For example, Daimler et al. U.S. Pat. No. 3,934,421 discloses a matting
comprising a plurality of continuous amorphous synthetic thermoplastic
filaments which
are bonded together at their intersections and can be used for the ground
stabilization of
road beds.
Marbling et al. U.S. Pat. No. 4,002,034 is directed toward a multi-layered
matting for inhibiting the: erosion of an embankment around a body of water,
the layer
closest to the water having less pore space and thinner fibers than the layers
away from
the water.
Bronner U.S. Pat. No. 4,329,392 discloses a hydraulic engineering matting
for inhibiting rearrangement of soil particles comprising a layer of melt-spun
synthetic
polymer filaments bonded at their points of intersection, a filter layer of
fine fibers
bonded thereto, and a third layer interdispersed therethrough.
Ter Burg et a.l. U.S. Pat. No. 4,421,439 discloses a supporting fabric or
matting for use on emba~~kments of roads, dikes, and the like. The fabric
generally
includes straight yarns in both the warp and weft directions with binder yarns
extending
in the warp direction and woven around the straight yarns of the weft
direction.
However, these yarns do not impart strength to the straight yarns.
Leach U.S. Past. No. 4,472,086 is directed toward a geotextile fabric for
erosion control having uncrimped synthetic threads in both the warp and
filling directions
and a known yarn stitch bonding the warp and filling threads together.
Finally, a comrnercially known high-profile structure generally used for soil
retention and erosion control which does employ heat-shrinkable yarns, but not
in a
single layer, is disclosed in Siancliffe et al. U.S. Pat. No. 4,762,581. This
patent relates
to high-profile structures or composites which are noted to be useful as
carpet underlay
and mattresses as well as embankment stabilization and drainage. These
structures are
believed to be commercially sold under the tradename, Tensar, and are
available from
Netlon Limited of Mill Hill, England.
However, the structures in Stancliffe et al. are provided by the welding of a
planar, biaxially heat-shrinkable, plastic mesh layer to a planar, relatively
non-heat-
CA 02497381 1994-09-15
. 1 V /.a a l . J I , 1. W 1. ~u.JJYn ... . . .
-4-
shrinkable plastic mesh layer at zones which are spaced apart on a generally
square grid.
Hence, when the heat-shrinkable layer is heated and shrinks, the non-heat-
shrinkable
layer assumes a generally cuspated configuration with the welded points on the
nan-heat-
shrinkable layer remaining in contact with the heat-shrinkable layer. This
patent does
not provide a single layer fabric and is susceptible to failure at the welding
points
bonding the layers together.
Thus, while attempts have been made heretofore to provide a suitable means
for stabilizing and retaining soil and for reinforcing turf, the art has not
provided a facile
means by which to do so. Accordingly, a need clearly exists for a single-
layered, high-
profile, three-dimensional, homogeneous fabric comprising fibers of differing
heat
shrinkage characteristics which will increase dimensional stability and last
longer than
other high-profile struchures commonly utilized for soil retention and
vegetative
reinforcement.
SUMMARY OF I1WENTION
It is, therefore, an object of the present invention to provide a three-
dimensional, high-profile, woven geotextile fabric suitable for use in soil
retention and
stabilization and vegetative reinforcement.
It is another object of the present invention to provide a geotextile fabric,
as
above, woven from monofilament yarns having different heat shrinkage
characteristics
such that, when heated, the fabric forms a thick three-dimensional, cuspated
profile.
It is yet another object of the present invention to provide a geotextile
fabric,
as above, which is single-layered and which has improved tensile strength,
modulus, and
dimensional stability, in combination, as compared to other single-layered
fabrics.
It is still another object of the present invention to provide a geotextile
fabric,
as above, which promotes easier handling and minimizes failure points, while
offering
a thick, strong and dimensionally stable product upon installation on slopes,
in ditches,
and other like places where: erosion control, turf reinforcement, and soil
stabilization may
t
be necessary.
CA 02497381 1994-09-15
WO 95/11757 PCT/U594110449
-5-
It is yet another object to provide a method for retaining and stabilizing
soil,
and reinforcing turf and vegetation, by placing a three-dimensional, high-
profile, woven
geotextile fabric into the soil.
At least one or more of the foregoing objects, together with the advantages
thereof over the known art relating to geotextile fabrics, which shall become
apparent
from the specification which follows, are accomplished by the invention as
hereinafter
described and claimed.
In general, tlhe present invention provides a method of stabilizing soil and
reinforcing vegetation comprising the step of placing a single-layered, three-
dimensional,
high-profile woven fabric into soil.
The present invention also includes a geotextile fabric comprising two sets
of monofilaments interwoven in substantially perpendicular direction to each
other, each
of the monofilaments having a pre-determined, different heat shrinkage
characteristics
such that, upon heating, the fabric forms a single-layer, three-dimensional,
cuspated
profile; the fabric having a tensile strength.of at least about 3200
pounds/foot in the warp
direction and at least about 2400 pounds/foot in the filling direction, a
modulus at 10
percent elongation of at least about 12500 poundslfoot in the warp direction
and at least
about 11000 pounds/foot in the filling direction, and a thickness of at least
about 500
mils. '
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of the fabric of the present invention;
Fig. 2 is a schematic view of the fabric of Fig. 1 showing its general
configuration;
Fig. 3 is an enlarged sectional view taken substantially along line 3-3 in
Fig. 2;
Fig. 4 is an enlarged sectional view taken substantially along line 4-4 in
Fig.
2.
CA 02497381 1994-09-15
"" .,..", ..,.",.,.v,.".
-6-
PREFERRED EMBODIMENT FOR CARRYING OUT TIIE INVENTION
As noted hereinabove, heretofore, mattings or geotextile structures suitable
for use in the stabilization and revegetation of soil have been largely mufti-
layered, high-
profile composite structures. The non-homogeneous nature of these composite
structures
as well as the possibility of weld failure in instances where the layers are
bonded together
are but two undesirable .characteristics often found in these structures.
Accordingly, a
single-layered, homogeneous, high-profile, woven geotextile fabric (not a
composite) as
the fabric of the present invention would appear to overcome these undesirable
characteristics, thereby improving the geotextile art.
A geotextile fabric embodying the concepts of the present invention is
generally indicated by the numeral 10 in the accompanying drawings and
includes two
sets of filaments 12 and 14 interwoven in substantially perpendicular
directions to each
other. As best shown in. Fig. 2, the filaments or fibers are initially,
preferably woven
into a type of pattern known in the weaving art as a "waffle weave" or
"honeycomb" type
of woven pattern. This weaving procedure, which is well known in the art and
can be
performed on essentially Ftny conventional textile weaving apparatus, produces
a generally
planar fabric with a distinctive look of adjacent pyramids on one side of the
fabric which
oppose and are offset from adjacent pyramids on the other side of the fabric.
Importantly, the filaments utilized to produce the geotextile fabric of the
present invention are bia~cially heat shrinkable. That is, upon being heated,
the filament
yarns will shrink in both directions. However, the amount of heat shrinkage is
different
for each filament dependiing upon its position within the woven fabric. Hence,
when the
woven, initially planar fabric 10 is subjected to heat, preferably from a hot
steam or
water bath, the filaments 12 and 14 are shrunk proportionally to the differing
levels of
heat shrinkage with which each filament was provided. Significantly, by
arranging the
filaments in a predetermined, well-known fashion based upon their level of
heat
shrinkage, the initially planar geotextile fabric 10 becomes thicker and more
three-
dimensional in shape. As seen in Figs. 3 and 4, the filaments provide a zig-
zag cross-
section and take up a substantially greater volume than when the fabric is
relatively
planar. Consequently, a three-dimensional, high-profile woven geotextile
fabric is
formed as shown in Fig. 1.
CA 02497381 1994-09-15
WO 95111757 '~ PCTIUS94110449
-
Moreover, the distinctive look of the fabric becomes more pronounced. That
is, the pyramidal shapes, within the fabric become significantly deeper and
more defined.
The thickness of the geotextile fabric preferably should grow to at least
about 0.5 inches
(500 mils) and more preferably, to about 0.65 inches (650 mils). It is this
thickness as
well as other characteri:;tics of this fabric which permit its use for soil
retention and turf
reinforcement.
For instance:, the fabric of the present invention preferably should have a
tensile strength of at least about 3200 pounds/foot in the warp direction and
at least about
2400 pounds/foot in the filling direction using the American Society for
Testing and
Materials' (ASTM) Standard Test Method D-4595. It should also preferably have
a
modulus at 10% elongation of at least about 12500 pounds/foot in the warp
direction and
at least about 11000 poundslfoot in the filling direction using the same ASTM
Test
Method, D-4595.
More desirably, the fabric has a tensile strength of at least about 4700
pounds/foot in the wasp direction and at least about 3500 pounds/foot in the
filling
direction using ASTM Standard Test Method D-4595. It should also preferably
have a
modulus at 10% elongation of at least about 18500 pounds/foot in the warp
direction and
at least about 16000 pounds%foot in the filling direction using the same ASTM
Test
Method, D-4595.
At this point, it should be noted that the filaments utilized in the
geotextile
fabric of the present invention are preferably thermoplastic monofilament yams
comprising such materials as polyethylene and polypropylene homopolymers,
polyesters,
polyphenylene oxide, certain fluoropolymers, and mixtures thereof. However, it
will be
understood that any materials capable of producing filaments or fibers
suitable for use
in the instant fabric of the present invention fall within the scope of the
present invention
and can be determined without departing from the spirit thereof. Most
preferably, the
filaments of the present invention are made of polypropylene, polyethylene,
high tenacity
polyester, or mixtures thereof.
Moreover, before more specifically detailing the operation of the present
invention, it should be understood that the process for making the geotextile
fabric is
well known in the art. A,s noted hereinabove, the weaving process can be
performed on
CA 02497381 1994-09-15
.1 V /Jr I I i J I 1~41n UJJiI ~U-~~iJ
- -
any conventional textile; handling equipment suitable for producing the fabric
of the
present invention and tlhus, a "honeycomb" type weave produced from
thermoplastic
polymeric yarns is also well-known in the art. However, it should be
understood that no
single-layered, homogeneous fabric has been employed for the purposes of the
present
invention. Importantly, because of the increased thickness of the fabric
provided by the
shrinkage of the pre-arranged filaments employed therein when subjected to
heat, the
subject invention can be; utili2ed in erosion control and veneer cover soil
and stability
applications.
In order to demonstrate that the geotextile fabric of the present invention is
suitable for its intended use, several tests on two fabrics produced according
to the
present invention were conducted. First, several tests were performed on
Fabric 1, a
three-dimensional, high-profile, woven polypropylene fabric. These tests were
conducted
according to standard test methods provided by the ASTM. The results of these
tests as
well as the test methods employed are presented in Table I hereinbelow.
CA 02497381 1994-09-15
WO 95/11757 ~'-'- PCTNS9~l/10.1:19
-9-
TABLE I
Fabric 1 Characteristics
PROPERTY TEST METHOD VALUE
Thickness ASTM D-1777 0.65 in
Resiliency ASTM D-1777 85
Weight ASTM D-3776 15.25 oz/sq. yd.
Tensile Strength2 ASTM D-4632 400 x 300 Ibs
'
ASTM D-4595 4,700 x 3,500 lbs/ft
Tensile Elongation2ASTM D-4632 35
ASTM D-4595 25
Modulus at 10%
Elongation2 ASTM D-4595 18,500 x 16,000
lbs/ft
GrOUnd Cover FBCtOt3Light Projection $~
Analysis
W Stability4 ASTM D-4355 80
lResiliency defined as percent of original thickness retained after 3 cycles
of a 100 psi
load for 60 seconds followed by 60 seconds without load - thickness being
measured 30
minutes after load removed by ASTM D-1777.
2Values for both machint: and cross machine directions under dry or
saturated~conditions.
3Ground Cover Factor represents "% shade" from Lumite Light Projection Test.
aTensile strength retained after 1000 hours in a Xenon ARC Weatherometer.
Next, several of the same tests were conducted on Fabric 2, a higher-strength,
three-dimensional, high-profile woven fabric comprising high tenacity
polyester and
polypropylene. The results of these tests as well as the test methods employed
are
presented in Table II hereinbelow.
CA 02497381 1994-09-15
- 10-
TABLE II
Fabric 2 Characteristics
PROPERTY TEST METHOD VALUE ..
Thickness ASTM D-1777 0.65 in
Resiliency' , ASTM D-1777 85
Weight ASTM D-3776 18.5 o~lsq. yd.
Tensile Strength2 ASTM D-4632 700 x 325 lbs
ASTM D-4595 7, I 00 x 3,200 lbs/ft
Tensile Elongation2 ASTM D-4632 30
ASTM D-4595 15
Modulus at 10% Elong~ation3ASTM D-4595 49,500 x 22,500 lbs/ft
Ground Cover F3CtOr4 Light Projection $0
Analysis
W Stabilitys ASTM D-4355 80
Aperture Size Measured 1.0 x 1.5 in
'Resiliency defined as percent of original thickness retained after 3 cycles
of a 100 psi
load for 60 seconds followed by 60 seconds without load - thickness being
measured 30
minutes after load removed by ASTM D-1777.
2Values for both machine and cross machine directions.
;Estimated values for both machine and cross machine directions based upon
limited
testing.
4Ground Cover Factor represents "% shade" from Lumite Light Projection Test.
STensile strength retained after 1000 hours in a Xenon ARC Weatherometer.
The resulting characteristics of the three-dimensional, high-profile Fabrics 1
and 2 were then compared to other fabrics similarly produced for other
purposes, such
as separation medium and tower packing. These conventional fabrics were
produced by
the Lumite Division of Synthetic Industries: The weight, thickness, tensile
strength and ,
UV stability of these fabrics are shown in Table III hereinbelow.
CA 02497381 1994-09-15
WO 95/11757 ~' ~ ~ PCT/US94/10449
-11-
TABLE III
Three Lumite Fabrics
PROPERTY FABRIC A FABRIC B FABRIC C
Weight (oz/sq. yd.)5.5 7.3 11.6
Thickness (mils) 65 60 200
Tensile Strength
(lbs/ft)
Warla 2,280 3,960 6,000
Fill 2,400 2,400 4,140
UV Stability Poor Poor Poor
Most notably, these known fabrics have a thickness generally of less than 200
mils (0.2
inches). Thus, the fabric of the present invention is three times as thick as
the well-
known Lumite fabrics. Moreover, Fabrics 1 and 2 have excellent ultraviolet
stability
while the Lumite fabrics tend to degrade much faster when subjected to
ultraviolet light.
Clearly, the Lumite fabric could not be utilized as a geotextile fabric for
soil erosion and
stabilization.
Continuing, it is believed that the combination of the thickness, strength and
modulus of the fabrics of the present invention permit high interface friction
angles under
saturated conditions resulting in superior veneer stability properties as
compared to other
geotextile structures, In order to demonstrate this particular improvement
over
conventional geotextile structures; an interface direct shear test was
conducted to evaluate
the interface shear resistimce between a soaked site cover soil and the
geotextile fabric
of the present invention.
More particularly, the test included three interface direct shear test trails,
each
of which was conducted at a different level of normal stress of about 100, 200
and 400
pounds per square foot (lbslsq. ft.), respectively, using a freshly prepared
test specimen
of woven geotextile fabric; embodying the concepts of the present invention
for each trial.
The same levels were employed far consolidation stress. The rate of shear for
each trial
was 0.04 inches per minute. The configuration of the trial specimens used in
the tests
were, from top to bottom., site cover soil, the geotextile fabric, and site
cover soil. For
CA 02497381 1994-09-15
-12-
each test trial, the upper cover soil was compacted directly on the geotextile
fabric
specimen and the entire trial specimen was tested under submerged conditions.
More specifiically, the interface direct shear test was generally performed in
accordance with ASTM Test Method D 5321, "Determining the Coefficient of Soil
and
Geosynthetic or Geosyr~thetic and Geosynthetic Friction by the Direct Shear
Method,"
said method being hereby incorporated by reference. The test trials were
conducted in
a large direct shear device which includes a shear box comprising an upper
component
and a lower component.. The upper component measured 12 inches by 12 inches
(300
mm X 300 mm) in plan .and 3 inches (75 mm) in depth. The lower component
measured
12 inches by 14 inches (300 mm X 360 mm) in plan and 3 inches (75 mm) in
depth.
A fresh test specimen made from Fabric 2 as noted hereinabove was prepared
for each of the three trials. Each geotextile fabric specimen was placed on
the top of the
compacted site cover soil in the lower shear box and attached to the lower
shear box with
mechanical compression clamps to confine failure to the interface between the
upper site
cover and the geotextile fabric.
For each test, fresh specimens of the site cover soil were compacted into the
lower shear box and were compacted directly on the geotextile fabric in the
upper shear
box. The site cover soil was compacted under as-received moisture conditions
by hand
tamping to the dry unit weight reported in Table IV for each normal stress
condition.
The reported moisture content and dry unit weight shown in Table IV are
average values
of the site cover soil in the lower and upper shear boxes. The reported values
of dry unit
weight were determined by measuring the as-placed volume of soil and dividing
this
volume into the calculated total dry weight of the soil specimen.
CA 02497381 1994-09-15 '~
wo ~snt~s~ ' rcT~s9aitoaa9
-13-
TABLE IV
Summary of Actual Interface Direct Shear
Test Equipment and Conditions
Test Trial No. 1 2 3
Shear Box Size 12" x 12" 12" x 12" 12" x 12"
TEST CONDITIONS:
Ydi~ 97.5 lbs/cu. ft. 96.9 lbslcu, ft. 97.2 lbs/cu. ft.
~ ci2 10.8% 10.5% 11.2%
Consolidation Stress100 lbs/sq. 200 lbs/sq. 400 Ibs/sq.
ft. ft. ft.
Time of Consolidation0 hours 0 hours 0 hours
(!0 cf3 14.9% 16.2% 16.1
Normal Stress 100 lbs/sq. 200 lbs/sq. 400 lbs/sq,
ft. ft. ft.
Displacement Rate 0.04 in/min 0.04 in/min 0.04 in/min
~~di refers to average initial dry unit weight of soil specimen in the upper
and lower
shear boxes in pounds/cuhic feet (lbs/cu, ft.).
Z(Bci refers to average irLitial moisture content of soil specimen in the
upper and lower
shear boxes.
3(~c f refers to average finial moisture content of soil specimen in the upper
and lower
shear boxes.
In addition, for each test, the entire test trial specimen, which included the
site wer soil in the lower and upper shear boxes and the geotextile fabric of
the present
invention, was submerged in tap water for approximately two to four minutes
prior to
applying normal stress. T'he entire test specimen remained submerged
throughout each
test. Furthermore, each specimen was sheared at a constant displacement rate
of about
0.04 inches/minute immediately after application of the normal stress. The
direction of
shear for each test was in the direction of manufacture (warp direction) of
the fabric
CA 02497381 1994-09-15
- 14-
J '.JI VW JY..\.. .i
samples. All of the trials were performed using a constant effective sample
area, where
the geotextile fabric v~ras larger than the upper sheax box. Consequently, no
area
correction was required when computing shear stresses. All of the trails were
sheared
until a constant, residual load was recorded.
The total stz~ess interface shearing resistance was evaluated for each applied
\
normal stress. The peak value of shear force was used to calculate the peak
shear
strength, and the residual shear strength was calculated from the stabilized,
post-peak
shear force which occurred at the end of each test. The total stress peak and
residual
shear strengths were de~zved from the test results plotted on a graph (not
shown) and are
presented in Table V hereinbelow.
TABLE V
Interface Direct Shear Test Results
Measured Peak and Residual Total Shear Strengths
Test Trial Measured Peak Measured Residual
Number Normal Stress Shear Strength Shear Strength
1 100 lb:Jsq. ft. 95 lbs/sq. ft. 95 lbslsq. ft.
2 200 lb:Jsq. ft. 150 Ibs/sq. ft. 150 Ibs/sq. ft.
3 400 lb:Jsq. ft. 280 lbslsq. ft. 280 Ibs/sq. ft.
Upon calculation of the shear strengths obtained for each test trial, the
results
were then plotted on a graph (not shown) of shear stress versus the
corresponding normal
stress to evaluate a total stress peak or residual strength envelope. A best
fit straight line
was drawn through the three data points from the test trials to obtain a total
peak stress
and residual stress interface friction angle and adhesion. The interface
friction angles and
adhesions derived from the plotted test results are summarized in Table VI
hereinbelow.
CA 02497381 1994-09-15
wo ~sm~s7 ' rc~rnJS9anoaa~
-15-
TABLE VI
Interface Direct Shear Test Results
Measured Total Stress Shear Strength Parameters
Tested Soaked Site Cover Soil/Fabric 2 Interface
(100 to 400 lbs/sq. ft.)
PEAK STRENGTH:
Friction Angle 32°
Adhesion 30 lbs/sq. ft.
RESIDUAL STRENGTH:
Friction Angle 32°
Adhesion 30 lbs/sq, ft.
For these teats, it is noted that the reported adhesion of 30 lbs/sq. ft.
corresponds to the shear axis intercept of the best fit straight line drawn
through the test
data points on the shear stress versus normal stress graph (not shown). This
value may
or may not be the true adhesion of the interface and caution should be
exercised in using
this adhesion value for applications involving normal stresses outside the
range of
stresses covered by the lest.
More notably, an interface friction angle of 32° under saturated
conditions
was obtained. This angle is approximately 15.6 percent higher than any other
interface
friction angle obtained udder saturated conditions with a soil reinforcement
material. The
best previous soil reinforcement material obtained only a 27° interface
friction angle
under saturated conditions. In view of these results, it is believed that the
fabric of the
present invention can improve the slope stability of slopes having from about
10° to 90°
angles (vertical slopes) as may be found in landfills, highways and the like.
In this test,
it is clear that the fabric of the present invention can improve slope
stability of 2.SH:1 V
side slopes (slopes of 22°).
Thus it should be evident that the geotextile fabric and method of the present
invention are highly effective in soil stabilization and retention and
vegetative
reinforcement. The inv~.ntion is particularly suited for use on slopes,
embankments,
CA 02497381 1994-09-15
- 16-
drainage ditches, subgrades, roadside beds, shorelines, and river or sea
walls, but is not
necessarily limited therf;to. The geotextile fabric of the present invention
can also be
used with other systems for vegetative reinforcement and erosion control,
although such
systems are no longer required when the geotextile fabric of the present
invention is
employed.
Based upon the foregoing disclosure, it should now be apparent that the use
of the geotextile fabric 2nd method of use described herein wilt carry out the
objects set
forth hereinabove. It is, therefore, to be understood that any variations
evident fall
within the scope of the claimed invention and thus, the selection of specific
component
elements can be determined without departing from the spirit of the invention
herein
disclosed and described.. In particular, the geotextile fabric of the present
invention is
not necessarily limited tn those comprising thermoplastic materials. Moreover,
as noted
hereinabove, any conventional method for production of the fabric can be used.
Thus,
the scope of the invention shall include all modifications and variations that
may fall
within the scope of the attached claims.
