Excavation Below Subgrade (EBS)

1. Excavation Below Subgrade (EBS) Topic G Topic G

2. EBS • QC/QV personnel do not determine/direct EBS operations. • Engineer ultimately determines the need for EBS. Topic G

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

4. Figure 3.1: Intercepting Embankment Topic G

5. 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

6. 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

7. Figure 3.2: Detail of EBS Topic G

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

9. Figure 3.3: EBS Topic G

10. Topic I

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

12. Figure 3.4: Rutting of Unstable Material Topic G

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

14. Figure 3.5: EBS Topic G

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

16. Figure 3.6: Backfilling EBS Topic G

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

18. Topic I

19. Figure 3.7: EBS Topic G

20. Figure 3.8: Loading Unstable Material Topic G

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

22. Figure 3.9: Backfilling EBS Topic G

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

24. Figure 3.10: Organic & Silty Soils Topic G

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

26. Figure 3.11: Seepage in a Cut Topic G

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

28. Figure 3.12: Dust Abatement Topic G

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

30. Figure 3.13: Stone Piles & Fences Topic G

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

32. Figure 3.14: Marsh Excavation 1 Topic G

33. Figure 3.15: Marsh Excavation 2 Topic G