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The Asphalt Core Embankment Dam A Very Competitive Alternative

The Asphalt Core Embankment Dam A Very Competitive Alternative. Prof. Dr. Kaare Höeg Norwegian Geotechnical Institute (NGI) and University of Oslo Athens, Greece,19 Nov. 2009. Svartevann Earth Core Rockfill Dam (129 m), Norway. Svartevann Dam under construction.

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The Asphalt Core Embankment Dam A Very Competitive Alternative

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  1. The Asphalt Core Embankment Dam A Very Competitive Alternative Prof. Dr. Kaare Höeg Norwegian Geotechnical Institute (NGI) and University of Oslo Athens, Greece,19 Nov. 2009

  2. Svartevann EarthCoreRockfill Dam (129 m), Norway

  3. Svartevann Dam under construction

  4. OddatjörnEarthCoreRockfill Dam, Norway (145 m)

  5. Oddatjörn Dam

  6. Storglomvatn Asphalt Core Dam, Norway(125m) plinth

  7. Storglomvatn Dam nearcompletion (125m)

  8. Compaction of asphalt concrete core and transition zones

  9. Experience with Asphalt Core Dams • 100 dams have been built, most in Europe and China, now also in North and South America; • 20 are currently under construction or final design; • first ones built in the early 1960s (Germany and Austria; • 15 built in Norway; 3 more are now under construction/final design;

  10. Field Monitoring • - The first dams with asphalt core were heavily instrumented and thoroughly analysed to better understand dam and core behaviour. • - Field performance has been excellent, with no recorded leakage through core or the core-plinth interface at the base of the core.

  11. Laboratory testing of asphalt concrete • For each new dam and site tests are performed to determine the optimum asphalt concrete mix using: • the available (local) aggregates (0-18 mm); • filler material (0 - 0.075mm); • grade of bitumen available. • The goal is to achieve a core with low permeabilty and flexible and ductile stress-strain behaviour with the required strength.

  12. Laboratory testing (cont’d) • Full advantage has been taken of all the laboratory and field research done for asphalt concrete used in road- and airfield pavements.

  13. Cross-section through a triaxial specimen

  14. Fuller’s grain size curve for aggregates

  15. Triaxial compression tests showing effect of confining stress level

  16. Splitting test of cylindrical specimen to determine tensile strength (Brazilian test)

  17. Beam test to determine flexural (tensile) strength and strain before crack opens

  18. Test to create crack in specimen

  19. Regain of tensile strength under compressive stress and sealing of crack

  20. Investigation of self-healing of crack

  21. Results of self-sealing test

  22. Triaxial test – cyclic loading superimposed on static loading (to simulate eartquake loading)

  23. Cyclic strain and residual strain during test

  24. Pre-cyclic vs. post-cyclic stress-strain behaviour Deviator stress (MPa)

  25. Asphalt concrete placed in core • Air porosity in asphalt core should be less than 3% to ensure very low permeabilty (10-10 m/s); • Placed and compacted in layers 20-30 cm thick; • 2 to 4 layers per day depending on required rate of construction; • Core width usually 50-100 cm depending on height of dam.

  26. Asphalt core placing machine (paver)

  27. Asphalt core paver – principle sketch

  28. Preparation of concrete plinth (placing mastic)

  29. Hand placement of first layers

  30. Machineplacement starts

  31. Test strip on site prior to core construction

  32. Compaction with 3 rollers

  33. Field samples (0.5 m long) drilled out of dam core(no interface can be detected between layers)

  34. Cutting field core into 5 test pieces

  35. Controlling field porosity

  36. Field control laboratory

  37. Field laboratory testing of mix from plant and of samples drilled out of the core

  38. Porosity control without sampling

  39. Excavated core from field test strip

  40. Demonstration of core flexibility in test section

  41. Demonstration of core flexibility (cont’d)

  42. Effect of laboratory method of compaction on resulting stress-strain properties of asphalt • Triaxial results from laboratory prepared and field core specimens with the same air porosity have been compared. • Differences in behaviour must be considered: • - if stress–strain design requirements (compression modulus, degree of shear dilation and ductility) are based on test results from laboratory prepared specimens; • - and if finite element analyses are used to predict or back-analyse core behaviour.

  43. Effect of laboratory compaction procedure (how to best simulate field compaction in the lab.)

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