9Compaction of asphalt concrete core and transition zones
10Experience 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;
11Field 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.
12Laboratory 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 ( mm);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.
13Laboratory 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.
26Pre-cyclic vs. post-cyclic stress-strain behaviour Deviator stress (MPa)
27Asphalt 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 cm thick;2 to 4 layers per day depending on required rate of construction;Core width usually cm depending on height of dam.
49Effect 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.
50Effect of laboratory compaction procedure (how to best simulate field compaction in the lab.)
57Back-calculated max.shear strain in core of Yele Dam
58Optimum Design Considerations Which embankment type is best suited for the local conditions, considering:- economy (construction and maintenance);- safety/reliability;- impact on the environment.The local foundation/geologic conditions will have significant impact on the choice of dam.
59Different embankment dam designs: - earth core embankment dam (ECED)- asphalt core embankment dam (ACED)- concrete faced rockfill or gravel dam (CFRD)- geomembrane faced embankment dam (GFED)- faced hardfill dam (FHD or CSGD)Recent comparisons among alternatives show the ACED to be very competitive.
60Asphalt concrete core - Simple and robust construction method; - Asphalt concrete is a flexible and ductile material with viscoelastic-plastic properties (a “forgiving” material);- No core erosion; therefore no strict filter criteria;- Core adjusts to dam and foundation deformations;- Earthquake resistant; no deterioration of properties;- Self-healing (self-sealing) of any cracks;- Asphalt mix may be ”tailored” to satisfy special design requirements;- Can resist overtopping erosion during construction;