CASE

STU

DIESCASE STUDIES

FOR INFRASTRUCTURE COMBIGRID®

APPLICATIONS

ah_naue_nr222_case_study_combigrid_12072012_1 13.07.2012 10:04 Seite 1

Ontario’s Highway 62 runs through numerousswampy areas. Significant stretches of theroad, like the province itself, overlie peatysoils. Properly maintaining roads in theseareas has historically been difficult due toissues of settlement, which have led tosubgrade breakdowns and roadway crack-ing and failures.

For a stretch of Hwy 62 south of Bancroft,the Ontario Ministry of Transportation,working with design engineering firmGolder Associates, sought a separation,reinforcement and drainage/filtration so-lution that would address and counter thetypical problems of road building over thearea’s peat.

Project engineers selected Combigrid®30/30 Q1 151 GRK 3 composite geogridsfor roadway reinforcement. This uniqueproduct from NAUE is composed of notjust a high-strength geogrid (Secugrid®)but also a needle-punched nonwoven geo-textile (Secutex®) - all in a single material.

This is the only composite product of itstype in the market. Rather than installingan individual geotextile and a geogridlayer, the site crews needed only to install

Combigrid®, which fea-tures the nonwoven geo-textile firmly weldedbetween the Secu-grid®'s reinforcementbars. In one layer, soilstabilisation, separa-tion and filtration/drainage is provided.For weak soils such asthose with a CBR valueless than 3%, the solu-tion is ideal. This heldtrue along Hwy 62. Theselection of the multi-

functional Combigrid® saved the projectteam time and money on installation whileensuring the long-term strength and performance desired in the project.

Combigrid® allowed for a shallow excava-tion (to the peat depth) and easy recon-struction. The reinforcing element reducedthe need for excessive aggregate and thegeotextile component ensured no mixing of disparate subgrade material.

Ultimately, the pavement structure was ableto be constructed as thin and lightweightand economically as possible without sacri-ficing roadway integrity. The risk of differ-ential settlement was dramatically reduced.

Also of note: the 4,75m wide Combigrid®rolls helped reduce waste on site and ex-pedite construction. Only two rolls of pro-duct were needed to cover the entire road-way reinforcement width as well as providea 300mm overlap for maximum assuranceof coverage and long-term strength.

During construction, one lane was rein-forced at a time while the other was leftopen to traffic. The composite geogrid rollswere unrolled in place and covered quicklyto reopen the lane as soon as possible.

Roughly 10,000sqm of Combigrid® 30/30 Q1151 GRK 3 were installed.

For Highway 62’s commuters, a smootherride has been provided, and it’ll be therefor a long time.

Road Building over Peat in Canada

Fig. 1Preparation of subgrade

Fig. 2Combigrid®installationover subgrade

ah_naue_nr222_case_study_combigrid_12072012_1 13.07.2012 10:04 Seite 2

The Sãlbatica Wind Farm in Romania’s Dobrogea region near Tulcea is in one of thebest places in Europe for the construction and operation of a wind farm. Its open lands possess some of the continent’s most dependable, strong winds. In Phase I of Sãlbatica, 70 2-MW turbines were con-structed. The annual production of the site (85.5 million kWh/year) has been enoughto power 29,000 homes.

Equally important is the site’s reduced carbonfootprint. Sãlbatica’s turbines produce power that if produced by traditional meansrelease 48,000 metric tons of CO2 per year.In the construction of Phase II, 35 2-MW Moline Gamesa G 90 were to be added. Theconstruction logistics involved in this construction are not simple. The towers are100m high and built of 5 segments thatweigh roughly 65 tons each.

For every wind turbine eight transport stages are needed: 5 for the pole segments, 1 for the blades, 1 for the nacelle, and 1 for thepropeller axle. Erecting them requires heavy

cranes. 7,50t Liebherr cranes were used, assisted by auxiliary cranes of 150, 200 and 500 tons. Without the aid of reinforce-ment, just getting the materials and equipment to the proper places on site would be a significant challenge. Site access roads are subject to tremendous loads and must be properly designed andsupported.

The existing resilient modulus at the roadwayexcavation level was 40-50MPa. This would not be sufficient to support the designedloads. Approximately 40km of access roadswere to be constructed and each turbinewould require its own crane hardstanding.Roughly 80 truckloads of crushed stone were delivered each day, and each truck carried 35 to 45 tons of aggregate.

The roads needed to resist 10,000 traffic cycles, and all of the oversized transportsmeant that additional loads of 65 to 95 tonsper truck were regularly on site. Furthermore,the crane pads’ concrete need required another 20 to 80 trucksper day. To maximise access, road performance,and survivability, engi-neers specified the in-stallation of 150,000m²of Combigrid® 30/30 Q1151 GRK 3C reinforce-ment geogrids.

Combigrid® is a uniquereinforcement productthat delivers four keygeosynthetic functionsin one composite mate-rial. NAUE’s patentedmanufacturing tech-niques combine the reinforcement strengthof a geogrid (NAUE

Secugrid®) with the filtration, separation and drainage of a nonwoven, needlepunchedgeotextile (Secutex®). The result is a robust,long-term reinforcement material that significantly improves soil bearing capacitywhile preventing any mixing of fines that might destabilise heavily-loaded roads.

The placement of a 200mm crushed stone(0 to 45mm) over Combigrid® produced amodulus of 90-130MPa. The placement of asecond 20cm crushed stone layer(0 to 63mm) obtained a modulus of 130-170MPa – more than safe for this design.

The 4,75m wide Combigrid® rolls also madeconstruction more convenient. Greater cov-erage per roll and easy installation meant amore efficient, more economical process. Lessdown-time, quicker access. The use of Combigrid® saved time and money and guaranteed immediate and long-term safetyand quality.

Combigrid® Reinforces theSălbatica Wind Farm, Romania

Fig. 3Completed

access road to a crane

hardstanding

Fig. 4Installation of instrumen-ted Combi-grid® sampleat a cranehardstanding

ah_naue_nr222_case_study_combigrid_12072012_1 13.07.2012 10:04 Seite 3

NAUE GmbH & Co. KGGewerbestrasse 232339 Espelkamp-FiestelGermany

Phone +49 5743 41-0Fax +49 5743 41-240E-Mail info@naue.comInternet www.naue.com

The information contained herein is the best to our knowledge, true and accurate. There is no implied or expressed warranty.© 2012 by NAUE GmbH & Co. KG, Espelkamp-Fiestel, Germany · All rights reserved. · No. 222 · Status 12.07.2012

®

Secugrid® and Combigrid® are registered trademarks of NAUE GmbH & Co. KG in various countries.

Geosynthetic separation and reinforcementmaterials are engineered for ground modifi-cation and improvement applications. One ofthe most common applications is base coursestabilization in roads. As traffic loads passover the roadway, the tensile forces can causecracking and rutting as the pumping actioninduced beneath the surface causes fine andcoarser aggregate to mix.

A separation geotextile prevents those aggre-gate layers from mixing. A reinforcement geo-grid redistributes those tensile forces and interlocks with the aggregate to prevent lateral migration. In both cases, roadway ser-vice lives are extended, performance improvedand standard maintenance greatly reduced.

Active roadways, however, are not the only installations that might require these func-tions from geosynthetics. Many construction projects themselves require separation and reinforcement geosynthetics to support the construction activities, such as when work isperformed over weak soils and heavy equip-ment is used.

This need was exemplified by a project inBrunei. During the construction of an inter-change, multiple cranes were placed on site tohandle various aspects of the construction,such as bore piles and materials movement forpiling and bridge construction. The area ex-perienced heavy rains during construction op-erations. These rains also not only delayedgeneral site work but caused significant

erosion. One of the cranes sank and toppledwhen it ventured too close to the unreinforcededge (see top picture). When the project team investigated the sunken crane, they dis-covered that the reinforcement and separa-tion geosynthetic installed beneath the working platform had not been extended farenough. Two of the primary cranes were unaffected because of the geosynthetic beneath them. The third crane was situatedonly upon the weak soil. As enough soil washed out from beneath it, the soil modulus became too weak to support thecrane.

Shortcuts Lead to a Longer RoadBrunei’s soft soils are primarily composed ofsandy, silty clays with high montmorillonitecontent or silty, peat soils. Annual precipita-tion is up to 1500mm. This often requires multiple geosynthetics to enable safe, heavy construction.

For the project site that experienced the collapse of one of its cranes due to weakenedsoils, a unique geosynthetic had been speci-fied. Manufactured by NAUE GmbH & Co. KG,the Combigrid® product provides both a separation geotextile and a reinforcementgeogrid in a single-layer product that cansimply be unrolled into position.

The needlepunched nonwoven layer is securedin the material during the manufacturingprocess and is sandwiched between the transverse and longitudinal high-strength

geogrid monolithic bars. This allows the pro-duct to provide reinforcement, as well as fil-tration, separation and drainage functions.

On site, the geosynthetic-supported zoneexperienced some erosion, but the base modulus was held in tact by the geocom-posite. Water penetrating the soil was able to drain through the geotextile, which also provided separation to prevent mixing.The cranes were supported.

Where the Combigrid® had not been installed,the base course on which the crane wasstanding mixed with the subbase and theplatform basically sunk. Also the waterwashed out the soil and both this caused the crane to topple.

With one storm and one photograph, we find an essential lesson about geosyntheticutilization depicted clearly. Not only can separation and reinforcement geosyntheticsprovide more durable and more economicalroadways, but the construction process itselfcan be made more efficient and less subjectto disruption.

Success vs. Sinking in Brunei

Fig. 5Placement ofbase coursematerial overinstalled Combigrid®

ah_naue_nr222_case_study_combigrid_12072012_1 13.07.2012 10:04 Seite 4