Excavation Below Subgrade (EBS)

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EBS• QC/QV personnel do not

determine/direct EBS operations.

• Engineer ultimately determines the need for EBS.

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EBS• Remove objectionable materials.

• Resulting excavation is then back filled with soil.

• Figure 3.1

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Figure 3.1: Intercepting Embankment

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Predicting EBS Areas

• Groundwater levels = 3 feet or less.• Silty “B” horizon.• Topsoil depths exceed 12 inches.• Moisture levels above plastic limit.• Depositional characteristics (alluvial,

lacustrine).

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Predicting EBS Areas

• Roadway constructed prior to 1940.• Extensive filling.• Roadway is distressed.• Highly variable soil conditions exist.• Subgrade is within 2 ft. of original

surface.

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Figure 3.2: Detail of EBS

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EBS

• Remove uncertain soil.• Note the diagonal rutting= unstable silt.• In addition to excavation.

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Figure 3.3: EBS

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Rutting of Unstable Material

• Transition from cut to fill are important.• Inspect before the subbase or base.• Rutting of unstable material shown.

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Figure 3.4: Rutting of Unstable Material

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EBS

• Yielding water-bearing silt.• Rock truck-hauling material away.• Backhoe-Loading EBS material out.• Dozer-Pushing material to backhoe.

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Figure 3.5: EBS

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Backfilling EBS

• EBS has to be measured.• Original section is template in the cross.• Final section–How much was excavated.

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Figure 3.6: Backfilling EBS

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EBS

• Do not do EBS when rain is imminent.

• Do not leave EBS excavation open over night.

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Figure 3.7: EBS

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Figure 3.8: Loading Unstable Material

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Backfilling EBS

• Careful placement and compact backfill.

• Use similar materials in area.

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Figure 3.9: Backfilling EBS

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Organic & Silty Soils

• Have foundation support for equipment.

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Figure 3.10: Organic & Silty Soils

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Seepage in a Cut

• Must correct area like this.• Ditches may work.–Riprapping–Underdrains

• Vegetation will not grow.

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Figure 3.11: Seepage in a Cut

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Dust Abatement

• Required to minimize dust. • Use water or dust control materials.

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Figure 3.12: Dust Abatement

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Stone Piles & Fences

• Large rocks outside the shoulder point.

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Figure 3.13: Stone Piles & Fences

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Marsh Excavation

• Picture 2:–Excavated marsh either cast out or

loaded into marsh.–Used for deeper marshes.

• Dragline works slower then backhoe.

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Figure 3.14: Marsh Excavation 1

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Figure 3.15: Marsh Excavation 2

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