No. 7 of 19 Soil Stabilization and Base Reinforcement by Ryan R. Berg, P.E.

1. No. 7 of 19Soil Stabilization and Base ReinforcementbyRyan R. Berg, P.E. The information presented in this document has been reviewed by the Education Committee of the International Geosynthetics Society and is believed to fairly represent the current state of practice. However, the International Geosynthetics Society does not accept any liability arising in any way from use of the information presented.

2. Lecture Outline • Definitions • Applications • Materials • Design • Specifications • Economics • Installation • Summary

3. Soil Stabilization Definition: • when a geosynthetic is placed at the subgrade/fill interface to increase the support of construction equipment over a weak or soft subgrade

4. Base Reinforcement Definition: • When a geosynthetic is placed as a tensile element at the bottom or within a flexible pavement base (or sub-base) course to: (i) improve the service life; (ii) obtain equivalent performance with a reduced structural section; or (iii) combination of (i) and (ii)

5. Soil Stabilization Applications: • Temporary roadways • Initial construction lift of permanent roads • Area construction platforms

6. Base Reinforcement Applications: • Permanent roads • Parking lots • Airport taxiways • Container loading facilities • Railway tracks

7. Materials Soil Stabilisation and Basal Reinforcement • Geotextiles • - Woven • - Nonwoven • Geogrids • - Extruded • - Knitted or Woven • Geogrid-Geotextile Composites

8. Design Soil Stabilisation and Basal Reinforcement Required Geosynthetic Properties Defined by Examining: • Design parameters • Survivability • Durability

9. Design Parameters Soil Stabilisation and Basal Reinforcement Design Parameters include: • Minimum acceptable rut depth • Traffic expected to use road • - wheel load/axle load • - number of axles • - number of passes • Foundation soil properties • - shear strength • - soil type

10. Design Soil Stabilisation and Basal Reinforcement Possible reinforcement mechanisms provided by geosynthetics: • Lateral restraint • Bearing capacity increase • Membrane tension support

11. Lateral Restraint

12. Bearing Capacity Increase

13. Membrane Tension Support

14. Placing Fill on Geotextile

15. Over Careful Placing

16. Subgrade Stabilisation Design • Several design methods are available • Design techniques mainly rely on: • - membrane tension, and • - bearing capacity increase • Check filtration • Most methods are generic; some are empirical- based, upon specific geosynthetic product

17. Subgrade StabilisationExample Design Methods • Stewart et al., 1977 • Barenburg, 1980 • Giroud and Noiray, 1981 • FHWA Geosynthetics Manual, • Holtz et al., 1998 • and others

18. Subgrade Stabilisation Specifications Design may be: (i) generic, or (ii) product-specific. Specification must follow design. Therefore, SPECIFICATION with (i) generic properties or (ii) Approved Products List may be appropriate.

19. Base Reinforcement Design • Several design methods exist • Design techniques mainly rely on: • Lateral restraint (or confinement), and • Bearing capacity increase • Check filtration • Most methods are empirical-based, upon specific geosynthetic product

20. Penner et al., 1985 Burd and Houlsby, 1986 Barksdale et al., 1989 Burd and Brocklehurst, 1990 Davies and Bridle, 1990 Miura et al., 1990 Sellmeijer, 1990 Webster, 1993 Dondi, 1994 Tensar, 1996 Wathugala et al., 1996 Akzo-Nobel, 1998 Zhao and Foxworthy, 1999 Base Reinforcement Example Design Methods

21. Base Reinforcement Specifications • Designs are usually empirical-based, upon product-specific performance. • Specification must follow design. Therefore, SPECIFICATION with an Approved Products List is usually appropriate.

22. Subgrade Stabilisation Economics • Geosynthetics provide cost savings in construction and maintenance of pavement structures • Savings are realized with decreased over- excavation and decreased required granular fill • Cost savings are often demonstrated by simply examining initial construction costs but, life cycle cost analysis may show additional, maintenance cost savings

23. Base Reinforcement Economics (Continued) • For some projects, cost savings may be demonstrated by simply examining initial construction cost • Will not be cost effective for all projects

24. Installation • Prepare the ground • Unroll the geosynthetic • Back dump aggregate • Spread the aggregate • Compact the aggregate

25. Prepare the Ground • remove the stumps, boulders, etc.; • fill in low spots.

26. Unroll the Geosythetic Directly over the ground to be stabilized. If more than one roll is required, overlap rolls.

27. Rolling out on Prepared Formation

28. Forming a Curve Using Folds

29. Forming a Curve Using Cut Pieces

30. Back Dump Aggregate • onto previously placed aggregate. • Do not drive on the geosynthetic. Maintain 150 mm to 300 mm cover between truck tires and geosynthetic.

31. Back Dumping Aggregate

32. Spread the Aggregate • over the geosynthetic to the design thickness.

33. Spreading Aggregate

34. Compact the Aggregate • using suitable compaction equipment.

35. Compaction of Aggregate

36. Repair of Rutted Section Subgrade Restraint • Fill in any excessive ruts formed during construction. • In no case should ruts be bladed down, as this would decrease the amount of aggregate cover between ruts.

37. Repair of Rutting with Additional Material

38. Summary Subgrade Geosynthetics are cost-effective, as subgrade restraint, to support construction equipment over soft soils

39. Summary Base Reinforcement Geosynthetics can be cost-effective for base reinforcement of flexible pavements to: - improve service life - obtain equivalent performance with a reduced structural section or combination of the two