Radial Stiffness of Secugrid - Global Synthetics

Secugrid® - Radial stiffnessTN-SG 1TECHNICAL NOTE

Figure 1Shear interactionbetween baseaggregate andSecugrid® geogridLoad distribution in geogrid reinforced base coursesThe use of geogrids to reinforce soft or compressiblefoundation soils for unpaved aggregateroads is one of the major application areas forgeogrids. Traffic loads which are applied to aggregateroad surfaces create lateral movementsinside the base aggregate. When a geogrid is installedbetween the subgrade and the base aggregate,shear interaction develops (Figure 1). This shearinteraction is also known as the "interlocking effect".The interlocking effect restrains the aggregate laterally(Figure 2) and transmits tensile forces from the aggregateto the geogrid. As the geogrid is much stiffer intension than the base aggregate, lateral stresses andstrains in the reinforced base aggregate are reduced andless vertical deformation (rut depth) in the road surfacecan be expected.Secugrid® - Radial stiffness · TN-SG 1Figure 2Efficiency ofSecugrid®geogridsThe interaction betweengeogrid and base aggregateincreases the elasticmodulus and thus thestiffness or load distributioncapacity of thebase course. This correlationenables the reductionof reinforced aggregatethicknesses in comparisonto un-reinforcedaggregate layers (Figure 3)or longer service lives ofthe reinforced sectionwith comparable basecourse thicknesses.2

Figure 3Increase of loaddistribution anglewith geogrids(Giroud et al. 1984)Secugrid® - Radial stiffness · TN-SG 1Stresses from traffic loads, which are transferred to thebase aggregate, lead to an outward motion of the aggregatefrom the wheel, mainly in the direction of thetraffic flow and perpendicular to it. Due to the shear interaction(interlocking) that is generated between thebase aggregate and the reinforcement, the geogrid ismainly stressed in longitudinal and transverse directions.This key reinforcement characteristic of a geogrid is alsoknown as the "tensile modulus" or "secant stiffness".Biaxial load distribution typically takes place where thetraffic flow is guided in defined directions across the installedgeogrid reinforcement, such as in roads and railwayapplications (Figure 4, bottom).In applications where a defined direction of traffic flowdoes not exist, such as in large traffic areas like parkinglots and container terminals (Figure 4, right), thegeogrid reinforcement might also be stressed diagonallyto the longitudinal and transverse (biaxial) direction.Regardless of which of these two different stress conditionsbecomes decisive, one of the main reinforcementfactors is the ability of the geogrid to absorb the mobilisedstresses at potentially low deformations.Figure 4Potential stressdirections ingeogrid reinforcementlayers3

Evaluation of geogrid stiffnessTo examine the tensile modulus or secant stiffnessvalues of Secugrid® geogrids in the conventionalbiaxial directions as well as diagonally to the longitudinaland transverse direction, tensile tests accordingto EN ISO 10319 have been carried out at tBU Institutfür textile Bau- und Umwelttechnik, Greven (Germany)that determined the radial geogrid stiffness at verylow deformations of 0.5% (Figure 5).Figure 5Radial Secant Stiffnessof Secugrid® geogridsat 0.5% elongationSecugrid® - Radial stiffness · TN-SG 1The test results show extremely high secant stiffnessvalues of ≥ 1,500 kN/m for Secugrid® 30/30 Q1and values of ≥ 2,000 kN/m for Secugrid® 30/30 Q6 inboth biaxial directions. Importantly, high secant stiffnessvalues of ≥ 592 kN/m for Secugrid® 30/30 Q1and ≥ 828 kN/m for Secugrid® 30/30 Q6 have alsobeen achieved diagonally to the longitudinal andtransverse directions.as for a multidirectional extruded polypropylene/PPgeogrid with triangular apertures. All test results of themeasured radial secant stiffness values at 0.5% strainfor the tested geogrids are shown in Figure 6. Thevalues show that the tested Secugrid® geogrids providethe highest radial stiffness values of all materials tested.To be able to compare the performance of Secugrid®geogrids to other reinforcement products, the same testswere carried out for woven and knitted geogrids as wellFigure 6Radial SecantStiffness ofdifferent geogridsat 0.5% elongation4

In Table 1 the minimum Radial Secant Stiffness valuesat 0.5% elongation of the examined geogrids aresummarized:GeogridSecugrid® 20/20 Q1 (PP)Secugrid® 30/30 Q6 (PP)Secugrid® 30/30 Q1 (PP)Radial Stiffness J0.5% [kN/m]≥ 494≥ 828≥ 592Secugrid® - Radial stiffness · TN-SG 1Secugrid® 40/40 Q1 (PP)≥ 802Knitted multifilament geogrid (PP)≥ 394Woven multifilament geogrid (PET)≥ 344Extruded biaxial geogrid (PP)Extruded multidirectional geogrid (PP) –Type 160*≥ 550UK datasheetUS datasheet≥ 505 ≥ 300Extruded multidirectional geogrid (PP) –Type 170** according to manufacturer’s product information≥ 580 ≥ 475Table 1Secant stiffnessvalues J 0.5% ofdifferent geogridsBased on the special manufacturing technique for Secugrid®geogrids, the flat, welded, pre-stressed polymerbars provide the desired high tensile modulus values(high tensile forces are absorbed at low strain levels)in longitudinal, transverse and diagonal directions,especially at the typically low strain rates which developinside geogrid reinforced aggregate base courses.NAUE GmbH & Co. KGGewerbestrasse 232339 Espelkamp-FiestelGermanyPhone +49 5743 41-0Fax +49 5743 41-240E-Mail info@naue.comInternet www.naue.comMemberships of the NAUE GroupMemberMember Member Member Member Member Member MemberMemberBentofix® BFG 5000Secugrid® Q6 and R6MemberMemberMemberMemberMemberMember Member Member MemberMember®and Secugrid® are registered trademarks of NAUE GmbH & Co. KG.The information contained herein is to the best of our knowledge, true and accurate. There is no implied or expressed warranty.© 2010 by NAUE GmbH & Co. KG, Espelkamp-Fiestel, Germany · All rights reserved. · TN-SG 1 · Status 08.12.2010 · *Patent No.: 6,572,718 B25