Geotextiles in Embankment Dams - Association of State Dam Safety ...

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Geotextiles in Embankment Damsneedlepunched nonwovens) exposed to rain absorb a considerable amount of waterand become difficult to handle should repositioning be required. All geotextiles usedas filters or transmissive media must be protected to prevent contamination by dust,dirt, and mud. In underwater applications, it is recommended that cover soils beplaced the same day.The covering operation must be carefully controlled to avoid damage to thegeotextile. Immediately prior to covering, the installed geotextile should beinspected to ensure it is still in proper position and that the subgrade has not beencompromised. The cover soil must meet the specification requirements. On slopes,cover soil placement should begin at the toe of a slope and proceed up the slope. Ageotextile can be damaged by equipment operating on too thin of a cover. For heavyequipment hauling, cover layers should be increased, see Figure 6.9. The maximumallowable slope on which soil cover can be placed is equal to the lowest soilgeotextilefriction angle. After the fill material is dumped, small low ground pressure(LGP) bulldozers and/or front end loaders may be used to spread the fill.The use of LPG dozers typically eliminates excessive puncture stresses on thegeotextile. However, of equal or greater importance is the shear stresses that aredeveloped along the subgrade soil/geotextile (lower interface) and soilcover/geotextile(upper interface) interfaces during the action of pushing the coversoil over the geotextile. The potential for large interface shear stresses exist when anequipment operator tries to push too much material up-slope at any one time. If theresulting shear stresses below the geotextile exceed the interface shear strength,localized slipping will result causing stretching in the up-slope direction. This maytear the geotextile. Many construction-quality assurance inspectors are unlikely torecognize this situation. Usually, inspectors focus on the minimum required coversoil thickness and look for evidence of damage below the dozers blade and tracks.Inspectors need to be aware of the need to avoid pushing thick layers of cover soil.An excavator can be used to safely reduce the height of high dump truck loads ofcover soil such as that seen in Figure 6.10. The trucks should not be allowed todump directly onto the geotextile. It is preferred to have the trucks dump onto apreviously placed layer of cover material.Typically, no additional compaction of the initial lifts is necessary as sufficientcompaction can be achieved by the static weight of the equipment. If compaction ofthe cover soil is required, the use of heavy equipment on the first lift should beavoided. A minimum of cover thickness of 12 inches should be maintained for lowpressure equipment operation. The maximum depth of soil placed in any one layershould not exceed 18 inches. The gradation and angularity of the cover soil is animportant variable. Coarse gravel covers should be placed no greater than 12 inches.Cover soils that have higher percentages of sand/clay or “pea gravel” such as thatshown in Figure 6.11 can be spread in up to 18 inch lifts.126
Chapter 6—Construction Methods and ConsiderationsFigure 6.9.—Photograph showing a haul road where the cover layer has been temporallyincreased to 5 feet to protect the geotextile from heavy equipment loading.Figure 6.10.—Photograph of an excavator removing the tops of thick piles of covermaterial. Attempting to move such thick piles with a bulldozer is likely to damage thegeotextile because of the high traction forces that would be required to push such a thicklayer of material.127
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Geotextiles in Embankment DamsStatu
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ContentsPreface ...................
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Geotextiles in Embankment Dams4.4.2
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Geotextiles in Embankment DamsFigur
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Geotextiles in Embankment Dams3.14
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Geotextiles in Embankment DamsCommo
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IntroductionGeotextiles are widely
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IntroductionExpansion of the roles
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Chapter 1Current Policy on the Use
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Chapter 1—Current Policy on the U
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Geotextiles in Embankment Damsfabri
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Geotextiles in Embankment Dams2.13.
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Geotextiles in Embankment DamsA-2
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FilterTucurui DamBrazil103 Nonwoven
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FilterAit ChouaritDam, Morocco150 N
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FilterTorcy-VieuxDam, France12.7 Ge
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FilterMany FarmsDam,Arizona, USA13.
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Protectivecushion for ageomembraneB
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Geotextiles in Embankment DamsREPOR
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SECTION 02342 - GEOTEXTILEPART 1GEN
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5 [Table 02342A. - Geotextile Sampl
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Table 02342B. - Geotextile Physical
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1. Cover material depth required fo
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3. Repair damaged geotextile by pla
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