Expanded multilayer integral geogrids and methods of making and using same
An expanded multilayer integral geogrid includes a plurality of oriented strands interconnected by partially oriented junctions having an array of openings therein that is produced from a coextruded or laminated multilayer polymer starting sheet. The integral geogrid has a multilayer construction, with at least one inner layer thereof having a structure that is expanded relative to at least one other layer of the multiple layers. By virtue of the expanded inner layer structure, the expanded multilayer integral geogrid provides for increased layer compressibility under load, resulting in enhanced material properties that provide performance benefits to use of the expanded multilayer integral geogrid in soil geosynthetic reinforcement, and economic benefits compared to a like integral geogrid without an expanded inner layer structure.
1 . A method of making an expanded multilayer integral geogrid, said method comprising:
providing a multilayer polymer sheet having a plurality of layers each of a polymeric material, with at least one inner layer of said plurality of layers capable of forming an expanded structure containing a distribution of voids therein;
providing a patterned plurality of holes or depressions in the multilayer polymer sheet; and
orienting the multilayer polymer sheet having the patterned plurality of holes or depressions therein to provide a plurality of oriented strands interconnected by partially oriented junctions and to configure the holes or depressions as grid openings, forming a repeating pattern of outer hexagons having an array of the grid openings therein, supporting ribs extending inwardly from each of the outer hexagons to support inside each of the outer hexagons a smaller inner hexagon having an open center and oriented strands and tri-nodes, the outer hexagons, the supporting ribs and the inner hexagons defining three different geometric configurations which are repeating throughout an entirety of the expanded multilayer integral geogrid, the oriented strands and the partially oriented junctions of the outer hexagon forming a plurality of linear strands that extend continuously throughout an entirety of the expanded multilayer integral geogrid, and the expanded multilayer integral geogrid having the plurality of layers each of the polymeric material extending throughout the geogrid,
the at least one inner layer having the expanded structure containing the distribution of voids in the expanded multilayer integral geogrid.
2 . The method according to claim 1 , wherein the at least one inner layer having the expanded structure includes a foam.
3 . The method according to claim 1 , wherein the at least one inner layer having the expanded structure includes a particulate filler.
4 . The method according to claim 1 , wherein the step of providing the multilayer polymer sheet is a step of coextruding.
5 . The method according to claim 1 , wherein the step of providing the multilayer polymer sheet is a step of laminating.
6 . The method according to claim 1 , wherein the multilayer polymer sheet having the patterned plurality of holes or depressions therein is oriented by uniaxial or biaxial stretching.
7 . The method according to claim 1 , wherein the multilayer polymer sheet includes a first layer, an expanded inner layer, and a third layer, with the first layer and the third layer being arranged on opposite planar surfaces of the expanded inner layer.
8 . The method according to claim 1 , wherein the multilayer polymer sheet has an initial thickness of at least 2 mm.
9 . The method according to claim 7 , wherein the multilayer polymer sheet first layer has a thickness of from about 0.5 mm to about 4.5 mm, the expanded inner layer has a thickness of from about 1 mm to about 9 mm, and the third layer has a thickness of from about 0.5 mm to about 4.5 mm.
10 . The method according to claim 7 , wherein the first layer has a material of construction of a polypropylene, the expanded inner layer has a material of construction of a virgin polypropylene or a recycled polypropylene, and the third layer has a material of construction of a polypropylene.
11 . The method according to claim 1 , wherein the at least one inner layer having the expanded structure has a void volume of from 5% to 60%.
12 . The method according to claim 1 , wherein the at least one inner layer having the expanded structure has a compressibility factor of from 5% to 75%.
13 . The method according to claim 2 , wherein the foam comprises a polypropylene and a foam additive.
14 . The method according to claim 3 , wherein the particulate filler is selected from the group consisting of a calcium carbonate, a hydrous magnesium silicate, a calcium sulphate, diatomaceous earth, a titanium dioxide, a nano-filler, a multi-wall carbon nanotube, a single wall carbon nanotube, a natural fiber, a synthetic fiber, dolomite, a silica, mica, and an aluminum hydrate.
15 . The method according to claim 1 , wherein the multilayer polymer sheet has a thickness of from about 2 mm to about 12 mm.
16 . A soil construction comprising a mass of particulate material strengthened by embedding therein an expanded multilayer integral geogrid produced as claimed in claim 1 .
17 . A method of strengthening a mass of particulate material, comprising embedding in the mass of particulate material the expanded multilayer integral geogrid produced as claimed in claim 1 .