Construction and Instrumentation of Geogrid-Reinforced Unpaved Road Test Sections

M. Hesham El Naggar

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: GEOSYNTHETICS

ABSTRACT: Geogridshave been used for decades as reinforcement to improve the performance of unpaved roads and therebyprolongtheirservicelife. Previous research efforts helpeddescribe the behavior of geogrid-reinforced unpavedstructures. However, more data from fieldtrials is needed tofully understand the reinforcing actionof geogridsin roadapplications. A research program was carried outinvolvingfull-scale unpaved road test sections reinforced with geogridsto evaluate the reinforcing mechanism of geogrids, quantify their effectiveness and provide an enhanced yet easy to usedesign toolfor practitioners. Ten test sections, each 14 m long, were constructed with two different base coursethicknesses. For each base course thickness, one section was unreinforced, while four were reinforced with geogridsthathavedifferent tensile strengths and aperture configurations. Geogrids were placed at the subgrade-base courseinterface on top ofnon-woven geotextileseparator. The sections were instrumented for measuring road response to bothcontrolled traffic and environmental loadings. This paper describes the construction and instrumentation of the testsections.R•SUM•G†ogrillesont †t† utilis†s pendant des d†cennies comme renfort pour am†liorer les performances des routes nonpav†es et prolonger leur dur†e de vie. Des efforts de recherche ant†rieurs ont aid† ‡ d†crire le comportement des routesnon pav†es renforc† avec g†ogrilles. Toutefois, plus de donn†es ‡ partir des essais sur le terrain est n†cessaire pourcomprendre pleinement le r…le de renfort de g†ogrilles. Un programme de recherche a †t† effectu†e sur la route nonpav† ‡ pleine †chelle sections d'essai renforc†e avec g†ogrilles ‡ †valuer le m†canisme de renforcement des g†ogrilles,quantifier leur efficacit† et leur fournir un meilleur pourtant facile ‡ utiliser en pratique outil de conception. Dix sectionsd'essais, chaque 14 m de long ont †t† construits avec deux diff†rentes †paisseurs de cours de base. Pour chaque coursde base de l'†paisseur, une section a†t† non renforc†e, tandis que quatre ont †t† renforc†es avec des g†ogrilles ayantdiff†rentes r†sistances ‡ la traction et configurations d'aperture. Les g†ogrilles sont plac†s ‡ l'interface entre la fond deforme et la couche d'agr†gat au-dessus du non-tiss† s†parateur g†otextile. Les sections ont †t† instrument†s pourmesurer la r†ponse de la route ‡ la circulation contr…l†e et charges environnementales.Cet article d†crit la constructionet l'instrumentation de l'sections d'essai.1INTRODUCTIONUnpaved roads are used widely to serve either temporaryor permanent transportation purposes.Theyarecommonlyconstructedwith base aggregates placeddirectlyoverweak subgradethat isincapable ofsupportinglargetraffic loads. Theseroads are prone toexcessive rutting,whichmayresultin interruption of trafficservice and increase of maintenance costs.In situationswhereexcavating and replacing unsuitable subgradematerialis not cost effective andpossiblytime consuming,stabilization with geosynthetics may be used.Geosynthetics have been used successfully fordecadesto improve the performance of unpaved roadsconstructed over weak subgrade.Theyprovideimprovedperformance and economical solution either throughminimizing initial cost or through reducing maintenancecost.Inclusion of a geosynthetic benefits the unpavedroad through two functions:separation and reinforcement.Reinforcement is the primary function (especially forgeogrids),which involves improving boththe subgradebearing capacity and theload distributionby the base.However,separation(typically performed by geotextiles)becomes an essential function when intermixing ofaggregateand subgrade soil islikely to occur.Possible mechanisms throughwhichgeogridsreinforcethe unpaved road include: 1) minimization ofdeterioration of the base layer by reducing lateralspreading of aggregate through interlock betweengeogrids and aggregate;2) increase of the base layerload distribution by adding tensile stiffness at the bottomof the base layer through —interlocking–;3) improvement ofload support via the —tensioned membrane effect– at largedeformation;and 4) improvement of subgrade bearingcapacity by confining the subgrade soil (Hufenus et al.2006; Giroud2009).Extensiveresearchhas been conducted over the pastfew decades to investigate the performance ofgeosynthetics in both paved and unpaved roads. Few fieldtestshave beencarried outto validate claims of improvingperformance of unpavedroadsowingto geosyntheticinclusion (Webster and Watkins1977; Little 1992; Fanninand Sigurdsson 1996; Hufenus et al.2006; Cuelho et al.2009, White et al. 2011). Similarly,field studies have beenconducted on roadway pavements to determine potentialbenefits of geosynthetics (Brandon etal. 1996; Al-Qadi

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