Plastic grid reinforcing
Some sites have an abundance of clean sand that by itself is not a very attractive embankment material. However, if the sand can be confined into small cells, it can be an acceptable material. Investigations into the enhancement of the load carrying capability of grid confined sand have been carried out at the United States Army Waterways Experiment Station (WES) in Vicksburg, Mississippi. Confinement of the unbound sand was achieved with a honeycomb-like grid material. Initial materials for the grid were paper, aluminum and plastic. In Alaska, Coetzee experimented with a high density polyethylene plastic grid confinement material manufactured by Presto Products Ltd. This grid can be shipped collapsed and deployed into a honeycomb-like grid at the site. The honeycomb is then filled with sand to form the grid confined layer. Results from
tests of the load carrying capability of the confined layers by both WES and Coetzee were encouraging and indicated that the confinement grids could give substantially improved performance when sand or other unbound aggregates are the only available local materials.
Coetzee used layered theory to evaluate a grid-confined sand layer. He reports that the results show that an 8 in. deep layer of grid-confined sand was better able to support applied wheel load than a 6 in. layer of gravel. Table 3. lists properties of the Presto GEOWEB® grid (Coetzee 1987).
TABLE 2. Average Thermophysical Properties of Selected Materials Thermal Conductivity Density Specific Heat
BTU/hr ft F Ibm/ft3) BTU/lbra F
Material (W/mK) (kg/m) (J/kgK)
LECA (expanded clay) |
|
|
|
Grade 1 |
0.09(0.15) |
12(280) |
— |
Grade 5 |
0.13(0.22) |
31(500) |
— |
EPS (extruded polystyrene) |
0.02(0.03) |
3.0(55) |
0.29(1210) |
Foamglass |
0.03 (0.06) |
9.0(145) |
0.24(1000) |
Gravel |
|
|
|
2% moisture |
0.90(1.6) |
130(2080) |
0.38(1591) |
Concrete |
0.81(1.4) |
144(2300) |
0.21(880) |
Snow (aged but undisturbed) |
0.06(0.10) |
15.6(250) |
— |
TABLE 3. Presto Geoweb Grid Information |
|
||
Material High-density polyethylene (HDPE)
Young's modulus Approximately 100.000 psi (6.9 X 105 kN/m2)
Ultimate strength and associated strain
in the direction of extrusion 3650 psi 455%
Normal to direction of extrusion 3065 psi 238%
Folded panel size 13 ft X 1 ft X 8 in.
Expanded panel size 8 ft X 20 ft X 8 in.
Sheets of HOPE per panel 60
Number of cells per panel 561
Approximate cell area (expanded) |
027ft2 |
Panel area |
154ft2 |
Thickness of HDPE sheet |
0. 055 in |
Shipping weight per panel |
122 lbm |
Coetzee(1987) |
|
Words and expressions: |
|
Reinforcing |
Укрепление, усиление |
Abundance |
Избыток, множество |
Load carrying capability |
Грузоперевозочная возможность |
To fill with sand |
Наполнять песком |
To encourage |
Ободрять, поддерживать |
To evaluate |
Определить |
Conductivity |
Проводимость |
Extrusion |
Вытеснение, выталкивание |
Approximately |
Приблизительно |
Weight |
Вес |