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Slope erosion protection with geogrids


In road construction, the demands for erosion control and reclamation beneficial to site and environment are outstandingly high. The effect of hydroseeding as protection against erosion, usually is reduced to the soil surface and the rooted soil horizon.

In order to restrain very loose soil geogrids with open weave design, which allows the planting of seeds, are installed offering strong support for vegetation.

The geogrids:

  • absorb the kinetic energy of the erosive elements (rain, wind) and stabilize the soil surface, creating over this numerous micro-dams,
  • keep the seeds and hydroseeding materials in place, even at steep slope soils, resulting in the successful germination of seeds
  • help the penetration of water into the soil and retain moisture, favouring thus the sprouting of the seeds, the rooting and good growth of grass.

The application of erosion control geotextiles, can increase and support the vegetation erosion control effect in areas with especially steep slopes or substrates susceptible to erosion.

A. ORGANIC GEOGRIDS

Organic geogrids possess the unique inherent features being composed of biologically and photo chemically degradable natural fibers. They are designed to retain soil in place until vegetation is established. By the time they start bio-degrading vegetation sprouts takes over its functions.
The organic geogrids have the following roles:

  • To absorb the kinetic energy of erosive elements (rain,wind)
  • To facilitate the infiltration of rain into the soil
  • To ratain moisture from rain: Besides being eco-concordant, they can absorb water to about five times its dry weight
  • To avoid the loss or dispersal of seeds installed for the revegetation
  • To favour the rooting of the established plant species
  • To control the temperature of the soil cushioning its natural oscillations: thus they can attenuate extremes of temperature and create a congenial micro-climate conducive to growth of vegetation.
  • To reduce the losses of soil moisture

Organic geogrids are the most flexible and drapable among most types synthetic geogrids. That allows them to conform the contour of the soil surface easily. The ability to make direct contact between the fibers and the soil develops a bond between soil, vegetation and the blanket reduce soil loss by 90% or more.

In addition to their reinforcing and anchoring function, organic geogrids act as mulches that enhance the establishment of vegetation. After degradation, they leave no toxic material.

A.1 Geojute

geojute

The Geojute geogrid is used to cover up slopes initially to give protection against erosion. Geojute yarns are thick with pronounced 3-D features and provide a series of mini barriers across the direction of overland flow, reducing the velocity runoff water. The openings of Geojute retain dislodged soil particles that are set to be carried away by the over land flow.
Geojute excellent drapability, allows it to shape to follow the soil contours on which it is laid. It absorbs water up to nearly from 4 - 5 times its dry weight, storing the rain fall water and preventing detachment of soil. In wet condition its flexibility increases further due to absorption of water.

Geojute, provides surface stability to steep slopes with angle up to approx. 45 deg.
Once vegetation starts growing, the role of Geojute is taken over by it. Geojute biodegrades in 2 years.
Geojute has a C factor = Soil Loss of protected surface divided by Soil Loss of unprotected surface of 0,005 and with a growth of dense vegetative cover it can protect 99.0 to 99.9 percent soil loss with a “C” factor of 0.001 to 0.01.

Structural characteristics Geojute Unit
Yarn Fiber Woven jute, undyed and unbleached
Yarn Count, Warp 6.5 threads/100mm approx.
Yarn Count, Weft 4.5 threads/100mm approx.
Color Natural (Brown, Earth Tone)
Fabric Weight 500 gr/m2
Open Area 60 -65 %
Durability 1-Φεβ yr
Mechanical characteristics Geojute 500 Unit
Thread tensile strength - warp 750 daN/M
Thread tensile strength - weft 450 daN/M
Open Area (%) 60 - 65 %
Absorption of water 485 % of dry weight
"C" Factor * 1.5:1 slope (without vegetation) 0,005
Roll format Geojute 500 Unit
Fabric Width 1220 mm
Length 70 m rolls or longer lengths in rolls and bales as required

slope-erosion-1

A2 Coir geogrid

coir-geogrid

The Coir geogrid is a strong and durable coir fiber mesh. The open weave design allows for planting of seeds and vegetation both before and after the mat has been installed, offering strong support for vegetation.
The semi-permanent design, allows the coir Geogrid erosion control mat to have a lifespan of approximately four to six years. During this time, the soil itself is gaining in shear strength either by increased densification and/or by consolidation. After this time, the mat will slowly biodegrade, enriching soil in the area, providing a natural erosion control disposal process.
Coir geogrid has hight tensile strength (35 KN/m) and elasticity and can be installed even on very steep slopes up to approx.70deg.

Structural characteristics Coir georgid 10 Unit
Yarn Fiber Spun, Twisted Coir
Fabric Weight (g/m2) 1.000
Color Natural (Brown)
Open Area (%) 50 - 60 %
Durability 4-Ιουν yr
Mechanical characteristics Coir georgid 10 Unit
Tensile strength (Length-Dry) 35 KN/M
Elongation at break - (Dry) 34 %
Roll format Coir georgid 10 Unit
Fabric Width 2000 mm
Length 50 m rolls or longer lengths in rolls as required

On steep slopes, which are more prone to erosion, organic georgids can be in placed in conjunction with the metallic mesh. The organic geogrids are best suitable for erosion protection through vegetative growth. Once the vegetation is established the organic geogrids serve no longer as a useful protection purpose. The metallic mesh remains for the permanent active or passive slope protection.
Geojute can be placed up to 60 deg with metallic mesh support, while coir geogrid in combination with metallic netting can be installed even on vertical slopes.
As presented, organic geotextiles are a very useful tool for protecting steep slopes until the vegetation takes over, which protects the surface permanently

B. SYNTHETIC GEOGRIDS

The beneficial role of vegetation on the slope erosion protection and stabilization is provided when the surface allows the establishment of vegetation and the expected velocity of water flowing over the surface is not of sufficient dura­tion and intensity to degrade the vegetative cover.
In severe applications (such as slopes with critical angle, high-flow channels, and pipe outlets) a vegetative cover, even well established vegetation may not be able to with­stand the erosive forces of water.
Therefore, a more resis­tant geosynthetic or metallic mesh cover must be employed and the surface that has been artificially augmented with an open structural coverage to increase its resistance to erosion above that of grass alone.

B1. TRM mat
Turf Reinforcement Mat

trm-mat

PRODUCT DESCRIPTION:
Trm mat is an erosion control mat preventing the slope erosion, made of 3 joined nets with a volumetric configuration: - 40 g/m2 PP BOP net as a base -125 g/m2 HDPE rhombic net as a base -125 g/m2 HDPE rhombic net giving the shape
Trm mat forms a dense layer preventing the added soil loss that helps the roots to stick in. The undulation net is the volumetrical mat and has the lodging cavities for the added soil.

Structural characteristics TRM MAT Unit
Polymer PP + HDPE
Colour (1) Black, Brown or Green
Net Configuration Complex
Weight 320 g / m2
Product Thickness 25 mm
Number of Undulations 22 n° / m
Undulation Mesh Size 10 x 10 mm x mm
Technical & Design Parameters TRM MAT Unit
Tensile Strength :
- 10 % Elongation 1,5 kN / m
- 20 % Elongation 2,5 kN / m
C-Factor (1) (Rain Intensity 150 mm/h, without vegetation) 0,3
Maximum Shear Stress (2) 288 (6) Pa (psf)
Roll format TRM MAT Unit
Dimension (m x m) 2 x 25 m
Diameter 52 cm
  1. C-Factor = Soil Loss with TRM mat protected surface divided by Soil Loss of unprotected surface
  2. Maximum Shear Stress (or Tractive Force) for tall fescue grass reinforced with TRM mat, grown into medium sand soil compacted at 90% Std. Proctor, assuming a reasonable soil loss of 1 cm.

TYPICAL APPLICATIONS:
Protection against erosion in slopes:

  • roads
  • railtracks,
  • urbanizations,
  • gardens,
  • landfills capping,
  • border edges

B2.TRM R

35/20, 55/20, 80/30, 110/30
Reinforced Erosion Control Mat

PRODUCT DESCRIPTION:

TRM R is a flexible geocomposite made by the erosion control mat TRM joined to INTERGRID, a polyester reinforcement geogrid of high tensile strength and low defromation.
The open and volumetric structure TRM R allows to retain soil layers in slopes, offering an increasement of the friction angle between the cover soil and the rest of geosynthetics (geomembrane, drainage geocomposite or bentonite clay linner). In addition, the high tensile strength and low creep of TRM R assure a long term reinforcement of the slope

TRM R
Structural characteristics 35/20 Trinter R 55/20 80/30 110/30 Unit
Polymer PP + HPDE + PET
Colour Black, brown or green
Net configuration Tridimensional grid + reinforced
Weight 480 490 580 620 g / m2
Product thickness 20-25 20-25 20-25 20-25 mm
Number of Undulations 22 22 22 22 n°/m
Undulation Mesh Size 10x10 10 x10 10 x10 10 x10 mm x mm
Technical & Design Parameters TRM R Unit
Peak tensile strength MD (1) 35 55 80 110 kN/m
Peak tensile strength CD (2) 20 20 30 30 kN/m
Elongation at break MD <12 <12 <12 <12 %
Elongation at break CD <12 <12 <12 <12 %
Roll format TRM R Unit
Dimension (m x m) 2 x 24 m
Diameter 52 cm

MD: machine direction (longitudinal)
CD: cross direction (transversal)

MAIN USES:

- erosion control of slopes of high inclination and length.
- protection of border edges.
- landfills capping.
- new landfills.
- vegetation over a geomembrane in waterpounds.

B3. GRID 12
Grid for erosion control

grid-12

PRODUCT DESCRIPTION:
U.V. stabilized polyethylene Grid 12 is designed to hold back soil, confine rock and facilitate greening. The technology used for it’s manufacturing is the «warp-knitting» process, which ensures the dimensional stability and solidity of the grids.
Geonets and geogrids made of UV-stabilized polyethylene ensure long-term soil retention.
The flexibility of the product means it follows the contours of the underlying ground, preventing the formation of voids at the grid-support. If the underlying ground is not being confined by the surface it will remain subject to the effects of subsurface water flow and erosion.
The use of Grid 12 allows to reduce the works area by creation of steeper slopes.Hydroseeding can facilitate greening immediately after the end of installation of the grid.

CHARACTERISTICS

Unit

Value

Margin

Mass per unit area

g/sqm

145

± 10%

Thickness under 2 kPa

mm

3

± 20%

Mesh size

mm

20 X 15

-

Colour

-

Dark green / natural

-

MECHANICAL PROPERTIES

Unit

Value

Margin

Tensile strength at break MD*

kN/m

12

Min. Value

Tensile strength at break CD*

kN/m

10

Min. Value

Elongation at break MD*

%

40

± 20%

Elongation at break CD*

%

85

± 20%

Roll format

Unit

Value

Fabric Width

m

3

Roll length

m

100

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APPLICATION

Soil confinement for steep slopes, use in conjunction with metallic nettings greening of slopes, landfill sites, ditches, overspill ponds, reservoirs. Easy to install, aids establishment of vegetation growth and roots development (open structure).