Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D17/00—Excavations; Bordering of excavations; Making embankments
  • E02D17/20—Securing of slopes or inclines
  • E02D17/202—Securing of slopes or inclines with flexible securing means
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D17/00—Excavations; Bordering of excavations; Making embankments
  • E02D17/20—Securing of slopes or inclines
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C11/00—Details of pavings
  • E01C11/16—Reinforcements
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
  • E01C3/00—Foundations for pavings
  • E01C3/006—Foundations for pavings made of prefabricated single units
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D3/00—Improving or preserving soil or rock, e.g. preserving permafrost soil
  • E02D3/005—Soil-conditioning by mixing with fibrous materials, filaments, open mesh or the like
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D2200/00—Geometrical or physical properties
  • E02D2200/16—Shapes
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D2300/00—Materials
  • E02D2300/0004—Synthetics
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D2300/00—Materials
  • E02D2300/0084—Geogrids

Definitions

• the present disclosure relates to a cellular confinement system, also known as a CCS or a geocell, which is suitable for use in supporting loads, such as those present on roads, railways, parking areas, and pavements.
• a cellular confinement system also known as a CCS or a geocell
• the geocells of the present disclosure retain their dimensions after large numbers of load cycles and temperature cycles; thus the required confinement of the infill is retained throughout the design life cycle of the geocell.
• a cellular confinement system is an array of containment cells resembling a "honeycomb" structure that is filled with granular infill, which can be cohesionless soil, sand, gravel, ballast, crushed stone, or any other type of granular aggregate. Also known as geocells, CCSs are mainly used in civil engineering applications that require little mechanical strength and stiffness, such as slope protection (to prevent erosion) or providing lateral support for slopes. [0003] CCSs differ from other geosynthetics such as geogrids or geotextiles in that geogrids / geotextiles are flat (i.e., two-dimensional) and used as planar reinforcement.
• Geogrids / geotextiles provide confinement only for very limited vertical distances (usually 1-2 times the average size of the granular material) and are limited to granular materials having an average size of greater than about 20 mm. This limits the use of such two-dimensional geosynthetics to relatively expensive granular materials (ballast, crushed stone and gravel) because they provide hardly any confinement or reinforcement to lower quality granular materials, such as recycled asphalt, crushed concrete, fly ash and quarry waste.
• CCSs are three-dimensional structures that provide confinement in all directions (i.e. along the entire cross-section of each cell).
• the multi-cell geometry provides passive resistance that increases the bearing capacity.
• a geocell provides confinement and reinforcement to granular materials having an average particle size less than about 20 mm, and in some cases materials having an average particle size of about 10 mm or less.
• Geocells are manufactured by some companies worldwide, including Presto. Presto's geocells, as well as those of most of its imitators, are made of polyethylene (PE).
• the polyethylene (PE) can be high density polyethylene (HDPE) or medium density polyethylene (MDPE).
• HDPE high density polyethylene
• MDPE medium density polyethylene
• the term "HDPE” refers hereinafter to a polyethylene characterized by density of greater than 0.940 g/cm 3 .
• MDPE refers to a polyethylene characterized by density of greater than 0.925 g/cm 3 to 0.940 g/cm 3 .
• the term low density polyethylene (LDPE) refers to a polyethylene characterized by density of 0.91 to 0.925 g/cm 3 .
• Geocells made from HDPE and MDPE are either smooth or texturized. Texturized geocells are most common in the market, since the texture may provide some additional friction of the geocell walls with the infill.
• HDPE theoretically can have a tensile strength (tensile stress at yield or at break) of greater than 15 megapascals (MPa), in practice, when a sample is taken from a geocell wall and tested according to ASTM D638, the strength is insufficient for load support applications, such as roads and railways, and even at a high strain rate of 150%/minute, will barely reach 14 MPa.
• the elevated temperature steps accelerate creep.
• the method enables extrapolation of the specimen's properties over long periods of time, even over 100 years.
• the load that causes plastic deformation of 10% is called the "long term design strength" and is used in geosynthetics as the allowed strength for designs. Loads that cause plastic deformation greater than 10% are avoided, because PE and PP are subject to second order creep above 10% plastic deformation. Second order creep is unpredictable and PE and PP have a tendency to "craze" in this mode.
• a vertical load When a vertical load is applied to a substrate of a granular material, a portion of that vertical load is translated to a horizontal load or pressure.
• the magnitude of the horizontal load is equal to the vertical load multiplied by the coefficient of horizontal earth pressure (also known as lateral earth pressure coefficient or L£PQ of the granular material.
• the LEPC can vary from about 0.2 for good materials like gravel and crushed stone (generally hard particles, poorly graded, so compaction is very good and plasticity is minimal) to about 0.3 to 0.4 for more plastic materials like quarry waste or recycled asphalt (materials that have a high fines content and high plasticity).
• the granular material When the granular material is wet (e.g. rain or flood saturating the base course and sub-base of a road), its plasticity increases, and higher horizontal loads are developed, providing increased hoop stress in the cell wall.
• HS d wherein HS is the average hoop stress in the geocell wall, VP is the vertical pressure applied externally on the granular material by a load, LEPC is the lateral earth pressure coefficient, r is the average cell radius and d is the nominal cell wall thickness.
• MPa megapascals
• geocells which provide sufficient stiffness and can accept high stresses without plastic deformation. Such geocells are suitable for load support applications such as pavements, roads, railways, parking areas, airport runways, and storage areas. Methods for making and using such geocells are also disclosed.
• a geocell formed from polymeric strips, at least one polymeric strip having a storage modulus of 500 MPa or greater when measured in the machine direction by Dynamic Mechanical Analysis (DMA) according to ASTM D4065 at 23°C and at a frequency of 1 Hz.
• DMA Dynamic Mechanical Analysis
• the at least one polymeric strip may have a storage modulus of 700 MPa or greater, including a storage modulus of 1000 MPa or greater.
• the at least one polymeric strip may have a stress at 12% strain of 14.5 MPa or greater when measured according to the Izhar procedure at 23 0 C 1 including a stress at 12% strain of 16 MPa or greater or a stress at 12% strain of 18 MPa or greater.
• the at least one polymeric strip may have a coefficient of thermal expansion of 120 x 10 '6 / 0 C or less at 25 0 C according to ASTM D696.
• the geocell may be used in a layer of a pavement, road, railway, or parking area.
• the geocell can be filled with a granular material selected from the group consisting of sand, gravel, crushed stone, ballast, quarry waste, crushed concrete, recycled asphalt, crushed bricks, building debris and rubble, crushed glass, power plant ash, fly ash, coal ash, iron blast furnace slag, cement manufacturing slag, steel slag, and mixtures thereof.
• a geocell formed from polymeric strips, at least one polymeric strip having a storage modulus of 150 MPa or greater when measured in the machine direction by Dynamic Mechanical Analysis (DMA) according to ASTM D4065 at 63 0 C and at a frequency of 1 Hz.
• DMA Dynamic Mechanical Analysis
• the at least one polymeric strip may have a storage modulus of 250 MPa or greater, including a storage modulus of 400 MPa or greater.
• the at least one polymeric strip may have a long term design stress of 3 MPa or greater, including a long term design stress of 4 MPa or greater
• FIG. 1 is a perspective view of a geocell
• FIG. 2 is a diagram showing an exemplary embodiment of a polymeric strip used in the geocells of the present disclosure
• FIG. 3 is a diagram showing another exemplary embodiment of a polymeric strip used in the geocells of the present disclosure
• FIG. 4 is a diagram showing another exemplary embodiment of a polymeric strip used in the geocells of the present disclosure
• FIG. 5 is a graph comparing the stress-strain results of various cells of the present disclosure against a comparative example
• FIG. 6 is a graph showing the stress-strain diagram for the geocells of the present disclosure
• FIG. 7 is a graph showing the results of a vertical load test for an exemplary cell of the present disclosure against a comparative example
• FIG. 8 is a graph of the storage modulus and Tan Delta versus temperature for a control strip
• FIG. 9 is a graph of the storage modulus and Tan Delta versus temperature for a polymeric strip used in the geocells of the present disclosure DETAILED DESCRIPTION
• FIG. 1 is a perspective view of a single layer geocell.
• the geocell 10 comprises a plurality of polymeric strips 14. Adjacent strips are bonded together by discrete physical joints 16. The bonding may be performing by bonding, sewing or welding, but is generally done by welding. The portion of each strip between two joints 16 forms a cell wall 18 of an individual cell 20. Each cell 20 has cell walls made from two different polymeric strips.
• the strips 14 are bonded together to form a honeycomb pattern from the plurality of strips. For example, outside strip 22 and inside strip 24 are bonded together by physical joints 16 which are regularly spaced along the length of strips 22 and 24. A pair of inside strips 24 is bonded together by physical joints 32. Each joint 32 is between two joints 16.
• an end weld 26 (also considered a joint) is made a short distance from the end 28 to form a short tail 30 which stabilizes the two polymeric strips 22, 24.
• the geocells of the present disclosure are made polymeric strips that have certain physical properties.
• the polymeric strip has a stress at yield, or at 12% strain when the polymeric strip has no yield point, of 14.5 MPa or greater when measured in the machine direction (perpendicular to seam plane in the geocell cell) at a strain rate of 20 %/minute or 150 %/minute.
• the polymeric strip has a strain of 10% or less at a stress of 14.5 MPa, when measured as described.
• the polymeric strip can withstand stresses of 14 MPa or greater without reaching its yield point.
• Other synonyms for the yield point include the stress at yield, the elastic limit, or the plastic limit.
• the stress is considered at 12% strain.
• These measurements relate to the tensile properties of the polymeric strip in the machine direction, at 23°C, not its flexural properties.
• the measurements are taken according to the following procedure, which is a modified version of said standards and is referred to herein as "the Izhar procedure”.
• a strip 50 mm long and 10 mm wide is sampled in the direction parallel to ground level and perpendicular to the seam plane of the cell (i.e. in the machine direction). The strip is clamped so that the distance between clamps is 30 mm.
• the strip is then stretched by moving the clamps away from each other at a speed of 45 millimeters (mm) per minute, which translates to a strain rate of 150%/minute, at 23 0 C.
• the load provided by the strip in response to said deformation is monitored by a load cell.
• the stress (N/mm 2 ) is calculated at different strains (the strain is the increment of length, divided by original length).
• the stress is calculated by dividing the load at specific strain by the original nominal cross-section (the width of the strip multiplied by the thickness of the strip) Since the surface of the geocell strip is usually texturized, the thickness of the sample is measured simply as "peak to peak" distance, averaged between three points on the strip.
• the polymeric strip may be characterized as having: a strain of at most 1.9% at a stress of 8 MPa; a strain of at most 3.7% at a stress of 10.8 MPa; a strain of at most 5.5% at a stress of 12.5 MPa; a strain of at most 7.5% at a stress of 13.7 MPa; a strain of at most 10% at a stress of 14.5 MPa; a strain of at most 11 % at a stress of 15.2 MPa; and a strain of at most 12.5% at a stress of 15.8 MPa.
• the polymeric strip may also have, optionally, a strain of at most 14% at a stress of 16.5 MPa; and/or a strain of at most 17% at a stress of 17.3 MPa.
• the polymeric strip may be characterized as having a stress of at least 14.5 MPa at a strain of 12%; a stress of at least 15.5 MPa at a strain of 12%; and/or a stress of at least 16.5 MPa at a strain of 12%.
• the polymeric strip may be characterized as having a storage modulus of 500 MPa or greater at 23 0 C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz.
• DMA Dynamic Mechanical Analysis
• the thickness for the DMA analysis is taken as "peak to peak" distance, averaged between three points.
• the DMA measurements described in the present disclosure are made according to ASTM D4065.
• the polymeric strip may be characterized as having a storage modulus of 250 MPa or greater at 50 0 C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz.
• DMA Dynamic Mechanical Analysis
• the polymeric strip may be characterized as having a storage modulus of 150 MPa or greater at 63°C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz.
• DMA Dynamic Mechanical Analysis
• the polymeric strip may be characterized as having a Tan Delta of 0.32 or less at 75 0 C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz. These novel properties are beyond the properties of typical HDPE or MDPE geocells.
• DMA Dynamic Mechanical Analysis
• Dynamic Mechanical Analysis is a technique used to study and characterize the viscoelastic nature of polymers. Generally, an oscillating force is applied to a sample of material and the resulting cyclic displacement of the sample is measured versus the cyclic loading. The higher the elasticity, the lower the time lag (phase) between the load and the displacement. From this, the pure stiffness (storage modulus) of the sample can be determined, as well as the dissipating mechanism (loss modulus) and the ratio between them (Tan Delta). DMA is also discussed in ASTM [0048] Another aspect of the geocell of the present disclosure is its lower coefficient of thermal expansion (CTE) relative to current HDPE or MDPE.
• CTE coefficient of thermal expansion
• the CTE is important because the expansion/contraction during thermal cycling is another mechanism that provides additional hoop stresses as well.
• HDPE and MDPE have a CTE of about 200 x 10 "6 / 0 C at ambient (23°C), and that CTE is even higher at temperatures greater than ambient.
• the geocell of the present disclosure has a CTE of about 150 x 10 ⁇ 6 / 0 C or less at 23 0 C, and in specific embodiments about 120 x 10 "6 / 0 C or less at 23°C when measured according to ASTM D696.
• the CTE of the geocell of the present disclosure has lower tendency to increase at elevated temperatures.
• Another aspect of the geocell of the present disclosure is its lower creep tendency under constant load.
• the lower creep tendency is measured according to accelerated creep test by stepped isothermal method (SIM), as described in ASTM 6992.
• SIM stepped isothermal method
• a polymeric specimen is subjected to a constant load under a stepped temperature program (i.e. the temperature is increased and held constant for a predefined period).
• the elevated temperature steps accelerate creep.
• the procedure of SIM test is applied to a sample of 100 mm width and net length of 50 mm (distance between clamps). The sample is loaded by a static load and heated according to a procedure comprising the steps:
• This SIM procedure is referred to herein as "the PRS SIM procedure”.
• the plastic strain (irreversible increase in length, divided by initial length) at the end of the procedure is measured.
• the plastic strain is measured against different loads, and the load that causes plastic strain of 10% or less is called the "long term design load.”
• the stress related to the long term design load is the "long term design stress” and provides the allowed hoop stress the geocell can tolerate for a long period of time under a static load,
• a typical HDPE geocell when subjected to the PRS SIM procedure, can barely provide a long term design stress of 2.2 MPa.
• the polymeric strip according to the present disclosure are characterized by a long term design stress of 2.6 MPa or greater, including a long term design stress of 3MPa or greater, or even 4 MPa or greater.
• the geocell of the present disclosure can provide significantly better properties up to 16% strain and in some embodiments up to 22% strain.
• the geocell can respond elastically to stresses greater than 14.5
• the geocell will provide the infill with a higher load bearing capacity and increased rebound to its original diameter under repeated loadings (i.e. cyclic loads).
• geocell of the present disclosure can be used with granular materials that generally cannot be used in base courses and sub-bases, as described further herein.
• the geocell of the present disclosure also enables better load bearing and fatigue resistance under humid conditions, especially when fine grained granular materials are used.
• the polymeric strip may include a polyethylene (PE) polymer, such as HDPE,
• MDPE or LDPE, which has been modified as described further below.
• the polymeric strip may also include a polypropylene (PP) polymer.
• PP polypropylene
• PP polypropylene
• Exemplary polypropylene polymers suitable for the present disclosure include polypropylene random copolymers, polypropylene impact copolymers, blends of polypropylene with either an ethylene-propylene-diene-monomer (EPDM) or an ethylene alpha-olefin copolymer based elastomer, and polypropylene block copolymers.
• EPDM ethylene-propylene-diene-monomer
• EPDM ethylene alpha-olefin copolymer based elastomer
• Such PP polymers are commercially available as R338-02N from Dow Chemical Company; PP 71 EK71 PS grade impact copolymer from SABIC Innovative Plastics; and PP RA1 E10 random copolymer from SABIC Innovative Plastics.
• Exemplary ethylene alpha-olefin copolymer based elastomers include Exact® elastomers manufactured by Exxon Mobil and Tafmer® elastomers manufactured by Mitsui.
• geocells of the present disclosure which incorporate PP may be less load-bearing and more restricted as to their operating temperatures than geocells of the present disclosure which incorporate HDPE.
• the PP and/or PE polymers or any other polymeric composition according the present disclosure are generally modified, through various treatment process and/or additives, to attain the required physical properties.
• the most effective treatment is post-extrusion treatment, either downstream from the extrusion machine, or in a separate process afterwards.
• lower crystallinity polymers such as LDPE, MDPE, and some PP polymers will require a post-extrusion process such as orientation, cross-linking, and/or thermal annealing, while higher crystallinity polymers can be extruded as strips and welded together to form a geocell without the need to apply post- extrusion treatment.
• the polymeric strip comprises a blend (usually as a compatibilized alloy) of (i) a high performance polymer and (ii) a polyethylene or polypropylene polymer.
• the blend is generally an immiscible blend (an alloy), wherein the high performance polymer is dispersed in a matrix formed by the polyethylene or polypropylene polymer.
• a high performance polymer is a polymer having (1 ) a storage modulus of 1400 MPa or greater at 23 0 C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz according to ASTM D4065; or (2) an ultimate tensile strength of at least 25 MPa.
• DMA Dynamic Mechanical Analysis
• Exemplary high performance polymers include polyamide resins, polyester resins, and polyurethane resins. Particularly suitable high performance polymers include polyethylene terephthalate (PET), polyamide 6, polyamide 66, polyamide 6/66, polyamide 12, and copolymers thereof.
• PET polyethylene terephthalate
• the high performance polymer typically comprises from about 5 to about 85 weight percent of the polymeric strip. In particular embodiments, the high performance polymer is from about 5 to about 30 weight percent of the polymeric strip, including from about 7 to about 25 weight percent.
• the properties of the polymeric strips can be modified either prior to forming the geocell (by welding of the strips) or after forming the geocell.
• the polymeric strips are generally made by extruding a sheet of polymeric material and cutting strips from said sheet of polymeric material, and the modification generally is made to the sheet for efficiency.
• the modification can be done in-line to the extrusion process, after the melt is shaped to a sheet and the sheet is cooled to lower than the melting temperature, or as a secondary process after the sheet is separated from the extruder die.
• the modification can be done by treating the sheet, strips, and/or geocell by cross-linking, crystallization, annealing, orientation, and combinations thereof.
• a sheet which is 5 to 500 cm wide may be stretched (i.e. orientation) at a temperature range from about 25 0 C to about 10 0 C below the peak melting temperature (Tm) of the polymeric resin used to make the sheet.
• the orientation process changes the strip length, so the strip may increase in length from 2% to 500% relative to its original length.
• the sheet can be annealed.
• the annealing may occur at a temperature which is 2 to 60 0 C lower than the peak melting temperature (Tm) of the polymeric resin used to make the sheet.
• Tm peak melting temperature
• the stretching and/or annealing is done at a temperature of from about 24 0 C to 15O 0 C.
• the annealing temperature is 2 to 60 0 C lower than the peak melting temperature (Tm) of the HDPE, MDPE, or PP phase.
• a polymeric sheet or strip is stretched to increase its length by 50% (i.e. so the final length is 150% of the original length). The stretching is done at a temperature of about 100-125 0 C on the surface of the polymeric sheet or strip. The thickness is reduced by 10% to 20% due to the stretching.
• a polymeric sheet or strip is cross-linked by irradiation with an electron beam after extrusion or by the addition of a free radical source to the polymeric composition prior to melting or during melt kneading in the extruder.
• the required properties for the geocell can be obtained by providing multi-layer polymeric strips. In some embodiments, the polymeric strips have at least two, three, four, or five layers.
• the polymeric strip 100 has at least two layers 110, 120, wherein two of the layers are made from same or different compositions and at least one layer is made of a high performance polymer or polymer compound having (1 ) storage modulus of 1400 MPa or greater at 23 0 C, measured in the machine direction by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz according to ASTM D4065; or (2) an ultimate tensile strength of at least 25 MPa.
• DMA Dynamic Mechanical Analysis
• one layer comprises a high performance polymer and the other layer comprises a polyethylene or polypropylene polymer, which may be a blend or alloy of a polyethylene or polypropylene polymer with other polymers, fillers, additives, fibers and elastomers.
• exemplary high performance resins include polyamides, polyesters, polyurethanes; alloys of (1 ) polyamides, polyesters, or polyurethanes with (2) LDPE, MDPE, HDPE, or PP; and copolymers, block copolymers, blends or combinations of any two of the three polymers (polyamides, polyesters, polyurethanes).
• the polymeric strip 200 has five layers.
• Two of the layers are outer layers 210, one layer is a core layer 230, and the two intermediate layers 220 bond the core layer to each outer layer (i.e. so the intermediate layers serve as tie layers).
• This five-layer strip can be formed by co- extrusion.
• the polymeric strip 200 has only three layers. Two of the layers are outer layers 210, and the third layer is core layer 230. In this embodiment, the intermediate layers 220 are not present. This three-layer strip can be formed by co-extrusion.
• the outer layers may provide resistance against ultraviolet light degradation and hydrolysis, and has good weldability.
• the outer layer can be made from a polymer selected from the group consisting of HDPE, MDPE, LDPE, polypropylene, blends thereof, and alloys thereof with other compounds and polymers. Those polymers may be blended with elastomers, especially EPDM and ethylene-alpha olefin copolymers.
• the core and/or outer layer can also be made from alloys of (1 ) HDPE, MDPE, LDPE, or PP with (2) a polyamide or polyester Each outer layer may have a thickness of from about 50 to about 1500 micrometers (microns)
• the intermediate (tie) layers can be made from functionalized HDPE copolymers or terpolymers, functionalized PP copolymers or terpolymers, a polar ethylene copolymer, or a polar ethylene terpolymer
• the HDPE and PP copolymers / terpolymers contain reactive end groups and/or side-groups which allow for chemical bond formation between the intermediate layers (tie layers) and the outer layer
• Exemplary reactive side-groups include carboxyl, anhydride, oxirane, amino, amido, ester, oxazoline, isocyanate or combinations thereof
• Each intermediate layer may have a thickness of from about 5 to about 500 micrometers
• Exemplary intermediate layer resins include Lotader® resins manufactured by Arkema and Elvaloy®, Fusabond®, or Surlyn® resins manufactured by DuPont
• the core and/or outer layer may comprise a polyester and alloys thereof with PE or PP, a polyamide and
• the polymeric strip 300 has three layers a top layer 310, a center layer 320, and a bottom layer 330
• the top layer is the same as the outer layer previously described
• the center layer is the same as the intermediate layer previously described
• the bottom layer is the same as the core layer previously described
• Geocells are generally embossed (textunzed by pressing the semi-solid mass after extrusion against a textunzed roll) to increase friction with granular infill or with soil Geocells may also be perforated to improve friction with granular infill and water drainage However, both embossing and perforation reduce the stiffness and strength of the geocell Since these friction aids are usually present, it is necessary to provide enhanced strength and stiffness to the geocell, by altering its polymer composition and/or morphology
• the polymeric strip may further comprise additives to attain the required physical properties. Such additives may be selected from, among others, nucleating agents, fillers, fibers, nanoparticles, hindered amine light stabilizers (HALS), antioxidants, UV light absorbers, and carbon black.
• additives may be selected from, among others, nucleating agents, fillers, fibers, nanoparticles, hindered amine light stabilizers (HALS), antioxidants, UV light absorbers, and carbon black.
• Fillers may be in the form of powders, fibers, or whiskers.
• Exemplary fillers include a metal oxide, such as aluminum oxide; a metal carbonate, such as calcium carbonate, magnesium carbonate, or calcium-magnesium carbonate; a metal sulfate, such as calcium sulfate; a metal phosphate; a metal silicate - especially talc, kaolin, mica, or wollastonite; a metal borate; a metal hydroxide; a silica; a silicate; an; an alumo-silicate; chalk; talc; dolomite; an organic or inorganic fiber or whisker; a metal; metal-coated inorganic particles; clay; kaolin; industrial ash; concrete powder; cement; or mixtures thereof.
• a metal oxide such as aluminum oxide
• a metal carbonate such as calcium carbonate, magnesium carbonate, or calcium-magnesium carbonate
• a metal sulfate such as calcium sulfate
• the filler has an average particle size of less than 10 microns, and in some embodiments, also has an aspect ratio of greater than one.
• the fillers is mica, talc, kaolin, and/or wollastonite.
• the fibers have a diameter lower than 1 micron.
• Nanoparticles can be added to the polymeric composition for various purposes. For example, inorganic UV-absorbing solid nanoparticles have practically no mobility and are therefore very resistant against leaching and/or evaporation. UV- absorbing solid nanoparticles are also transparent in the visible spectrum and are distributed very evenly. Therefore, they provide protection without any contribution to the color or shade of the polymer.
• Exemplary UV-absorbing nanoparticles comprise a material selected from the group consisting of titanium salts, titanium oxides, zinc oxides, zinc halides, and zinc salts.
• the UV-absorbing nanoparticles are titanium dioxide.
• Examples of commercially available UV-absorbing particles are SACHTLEBENTM Hombitec RM 130F TN, by Sachtleben, ZANOTM zinc oxide by Umicore, NanoZTM zinc oxide by Advanced Nanotechnology Limited and AdNano Zinc OxideTM by Degussa.
• the polymeric strips from which the geocell is formed are made by various processes.
• the process comprises melting a polymeric composition, extruding the composition through an extruder die as a molten sheet, forming and optionally texturizing the resulting sheet, treating the sheet as needed to obtain the desired properties, cutting the sheet to strips, and welding, sewing, bonding, or riveting strips formed from the sheet together into a geocell.
• the various components such as the polymeric resins and any desired additives are melt kneaded, usually in an extruder or co-kneader.
• an extruder such as a twin- screw extruder or single screw extruder with enough mixing elements, which provides the needed heat and shearing with minimal degradation to the polymer.
• the composition is melt kneaded so that any additives are thoroughly dispersed.
• the composition is then extruded through a die, and pressed between metal calendars into sheet form.
• Exemplary treatments provided downstream of the extruder die include texturing the surface of the sheet, perforating the sheet, orientation (uni-directional or bidirectional), irradiation with electron beam or x-rays, and thermal annealing.
• the sheet is heat treated to increase crystallinity and reduce internal stresses.
• the sheet is treated to induce cross linking in the polymeric resin by means or electron beam, x-ray, heat treatment, and combinations thereof. Combinations of the above treatments are also contemplated.
• Strips can be formed from the resulting sheet and welded, sewed, or bonded together to form a geocell. Such methods are known in the art. The resulting geocell is able to retain its stiffness under sustained load cycling over extended periods of time.
• the geocells of the present disclosure are useful for load support applications that current geocells cannot be used for.
• the present geocells can also use infill materials that are typically not suitable for load support applications for base courses, subbases, and subgrades
• the geocells of the present disclosure allow the use of materials for the infill that were previously unsuitable for use in load support applications, such as base courses and subbases, due to their insufficient stiffness and relatively poor fatigue resistance (in granular materials, fatigue resistance is also known as resilient modulus).
• Exemplary granular infill materials that may now be used include quarry waste (the fine fraction remaining after classification of good quality granular materials), crushed concrete, recycled asphalt, crushed bricks, building debris and rubble, crushed glass, power plant ash, fly ash, coal ash, iron blast furnace slag, cement manufacturing slag, steel slag, and mixtures thereof.
• the load at different deflections was measured or translated to Newtons (N).
• the deflection is measured or translated to millimeters (mm).
• the stress was calculated by dividing the load at a specific deflection by the original cross-section of the strip (original width multiplied by original thickness, wherein thickness is the nominal peak-to peak distance between upper face and bottom face).
• the strain (%) was calculated by dividing the specific deflection (mm) by the original length (mm) and multiplying by 100.
• the geocell was non-perforated. Its stress-strain response according to the Izhar procedure and is shown in Table 1.
• An HDPE strip was extruded, and embossed to provide a texture similar to Comparative Example 1.
• the strip had a thickness of 1.7 mm, and was then stretched at a temperature of 100 0 C (on the strip surface) so that the length was increased by 50% and the thickness was reduced by 25%.
• the stress-strain response of this HDPE strip was measured according to the Izhar procedure and is shown in Table 2,
• Example 1 maintained an elastic response up through 12% strain without a yield point and without reaching its plastic limit and at stresses greater than 17 MPa. The recovery of initial dimensions, after release of load, was close to 100%.
• a high performance polymeric alloy composition comprising 12 wt% polyamide 12, 10 wt% polybutylene terephthalate, 5% polyethylene grafted by maleic anhydride compatibilizer (Bondyram® 5001 manufactured by Polyram), and 73% HDPE was extruded to form a texturized sheet of 1.5 mm thickness.
• the stress-strain response of a strip formed from the composition was measured according to the Izhar procedure and is shown in Table 3.
• Example 2 maintained an elastic response up through 14% strain and at stresses greater than 17 MPa 1 without a yield point and without reaching its plastic limit. The recovery of initial dimensions, after release of load, was close to
• FIG. 5 is a graph showing the stress-strain results for Comparative Example
• Example 1 and Example 2 have no sharp yield point, and maintained increase in stress without yield up to 12-14% strain at stresses of greater than 17 MPa, while the Comparative Example 1 reached its yield point at 8-10% strain and a stress of about 14 MPa. This translates into a greater range at which an elastic response is maintained.
• the fact that no yield point was observed for Example 1 and Example 2 is important when cyclic loading is expected and the ability to return to the original dimensions (and thus the maximal confinement of infill) is crucial.
• FIG. 6 is a graph showing the difference between the stress-strain result of Comparative Example 1 and a polymeric strip of the present disclosure which is characterized as having a strain of at most 1.9% at a stress of 8 MPa; a strain of at most 3.7% at a stress of 10.8 MPa; a strain of at most 5.5% at a stress of 12.5 MPa; a strain of at most 7.5% at a stress of 13.7 MPa; a strain of at most 10% at a stress of 14.5 MPa; a strain of at most 1 1% at a stress of 15.2 MPa; a strain of at most 12.5% at a stress of 15.8 MPa; a strain of at most 14% at a stress of 16.5 MPa; and a strain of at most 17% at a stress of 17.3 MPa.
• the area to the left of the dotted line defines the combinations of stress-strain according to the present disclosure.
• each cell was 10 cm high, 33 cm between seams, embossed, non perforated, and had a thickness of 1.5 mm.
• the cell was opened so that its long "radius" was about 260 mm and its short radius was about 185 mm.
• a sandbox of 800 mm length and 800 mm width was filled to 20 mm depth with sand.
• the sand gradation distribution is provided in Table 4,
• the cell was placed on the surface of this sand and filled with the same sand.
• the expanded cell had a roughly elliptical shape, about 260 mm on the long axis and about 180 mm on the short axis. Additional sand was then placed into the sandbox to surround the cell and bury the cell so that a top layer of 25 mm covered the cell. The sand was then compacted to 70% relative density.
• a piston of 150 mm diameter was placed above the center of the cell and the load was increased to provide pressure on the sand surface in 50 kPa increments (i.e. the pressure was increased every 1 minute by 50 KPa).
• the deflection (penetration of piston into the confined sand) and pressure (vertical load divided by piston area) were measured.
• Example 2 continued to perform elastically at pressures greater than 400 kPa, whereas the cell of Comparative Example 1 did not. Due to the yielding of the HDPE wall, poor confinement was observed in the ceil of Comparative Example 1.
• the yield point for Comparative Example 1 was at vertical pressure of about 250 KPa, and if the average hoop stress is calculated (average diameter of cell is 225 mm) at that vertical pressure, a value of about 13.5 MPa is obtained. This number is in very good agreement with the yield point values obtained by the stress-strain tensile measurements according to the Izhar procedure.
• FlG. 7 is a graph showing the results in Table 5. The difference in resistance to penetration (i.e. how well the cell supported the vertical load) is very clear.
• a polymeric strip was made according to Example 2.
• an HDPE strip of 1.5 mm thickness according to Comparative Example 1 was provided.
• the two strips were then analyzed by Dynamic Mechanical Analysis (DMA) at a frequency of 1 Hz according to ASTM D4065.
• the control HDPE strip was tested over a temperature range of about -15O 0 C to about 91 0 C.
• the control strip was heated at 5°C/min and the force, displacement, storage modulus, and tan delta were measured.
• the polymeric strip of Example 2 was tested over a temperature range of about -65 0 C to about 120 0 C.
• the control strip was heated at 5°C/min and the force, displacement, storage modulus, and tan delta were measured.
• FlG. 8 is a graph of the storage (elastic) modulus and Tan Delta versus temperature for the control HDPE strip.
• FIG. 9 is a graph of the storage (elastic) modulus and Tan Delta versus temperature for the polymeric strip of Example 2,
• the storage modulus of the HDPE decreased more rapidly than the storage modulus of Example 2.
• the storage modulus for the strip of Example 2 was almost three times higher than the storage modulus for the HDPE strip at 23°C.
• the strip of Example 2 had to be heated to almost 6O 0 C, i.e. the strip of Example 2 maintained its storage modulus better.
• the Tan Delta for the HDPE strip increased exponentially starting at around 75°C, indicating a loss of elasticity (i.e. the material became too plastic and would not retain sufficient stiffness and elasticity), so that the strip was viscous and plastic. This is undesirable, as geocells can be heated even when placed underground (such as in a road).
• the Tan Delta for the strip of Example 2 maintained its properties at temperatures as high as 100 0 C. This property is desirable as it provides an additional safety factor. Since performance at elevated temperatures is a way to predict long term performance at moderate temperatures (as described in ASTM 6992), the fact that HDPE began losing its elasticity and thus its load support potential at about 75 0 C within seconds, provides some insight about its poor creep resistance and tendency to plastically deform. Unlike HDPE, the composition according to the present disclosure, kept its elasticity (low Tan Delta) at very high temperatures, thus suggesting that it has the potential to retain its properties for many years and many loading cycles.
• HDPE strip was made according to comparative example 1.
• the first test strip was one made according to Example 2.
• the second test strip was one made according to Example 2, then oriented at 1 15 0 C to increase its original length by 40%). The results are shown in Table 6 below. Table 6.

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