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. Topic G

EBS Remove objectionable materials. Resulting excavation is then back filled with soil. Figure 3.1 Topic G

Figure 3.1: Intercepting Embankment Topic G

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). Topic G

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. Topic G

Figure 3.2: Detail of EBS Topic G

EBS Remove uncertain soil. Note the diagonal rutting= unstable silt. In addition to excavation. Topic G

Figure 3.3: EBS Topic G

Topic I

Rutting of Unstable Material Transition from cut to fill are important. Inspect before the subbase or base. Rutting of unstable material shown. Topic G

Figure 3.4: Rutting of Unstable Material Topic G

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

Figure 3.5: EBS Topic G

Backfilling EBS EBS has to be measured. Original section is template in the cross. Final section How much was excavated. Topic G

Figure 3.6: Backfilling EBS Topic G

EBS Do not do EBS when rain is imminent. Do not leave EBS excavation open over night. Topic G

Topic I

Figure 3.7: EBS Topic G

Figure 3.8: Loading Unstable Material Topic G

Backfilling EBS Careful placement and compact backfill. Use similar materials in area. Topic G

Figure 3.9: Backfilling EBS Topic G

Organic & Silty Soils Have foundation support for equipment. Topic G

Figure 3.10: Organic & Silty Soils Topic G

Seepage in a Cut Must correct area like this. Ditches may work. Riprapping Underdrains Vegetation will not grow. Topic G

Figure 3.11: Seepage in a Cut Topic G

Dust Abatement Required to minimize dust. Use water or dust control materials. Topic G

Figure 3.12: Dust Abatement Topic G

Stone Piles & Fences Large rocks outside the shoulder point. Topic G

Figure 3.13: Stone Piles & Fences Topic G

Marsh Excavation Picture 2: Excavated marsh either cast out or loaded into marsh. Used for deeper marshes. Dragline works slower then backhoe. Topic G

Figure 3.14: Marsh Excavation 1 Topic G

Figure 3.15: Marsh Excavation 2 Topic G