Excavation Below Subgrade (EBS) Topic G. EBS QC/QV personnel do not determine/direct EBS operations....
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Transcript of Excavation Below Subgrade (EBS) Topic G. EBS QC/QV personnel do not determine/direct EBS operations....
Excavation Below Subgrade (EBS)
Topic G
Topic G
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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