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HVSIA Costa Rica 21 -23 Aug 2013. Technical discussion FWD vs roling wheel deflections. Louw du Plessis. Contents. Problem definition FWD data collection & analysis process MDD system Experimental pavement Results Analysis Conclusions. FALLING WEIGHT DEFLECTOMETER (FWD).
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HVSIA Costa Rica 21 -23 Aug 2013 Technical discussion FWD vs roling wheel deflections Louw du Plessis
Contents • Problem definition • FWD data collection & analysis process • MDD system • Experimental pavement • Results • Analysis • Conclusions
Impulse Load Stress Zone Base Subbase Subgrade
Offset from Load Centre Outer Part of Bowl (affected by subgrade and substratum) Deflection Middle Part of Bowl (affected by middle pavement layers) Inner Part of Bowl (affected by upper pavement layers)
Maximum Deflection (YMax) • Evaluates Overal Pavement Stiffness • YMax = D0 • YMax < 250 micron : Relatively Stiff Pavement • 250 < YMax < 500 micron : Medium Stiff Pavement • YMax > 500 : Relatively Weak Pavement • Important: These are only ROUGH guidelines, based on RSA Experience Only!
Base Layer Index (BLI) • Evaluates Upper Pavement Zone Stiffness • Typically Surfacing and Base Layers • BLI = D0 – D300 • BLI < 130 micron : Relatively Stiff Upper Zone • 130 < BLI < 180 micron : Medium Stiff Upper Zone • BLI > 180 : Relatively Weak Upper Zone • Important: These are only ROUGH guidelines, based on RSA Experience Only!
Middle Layer Index (MLI) • Evaluates Middle Pavement Zone Stiffness • Typically Subbase Layers • MLI = D300 – D600 • MLI < 70 micron : Relatively Stiff Middle Zone • 70 < MLI < 90 micron : Medium Stiff Middle Zone • MLI > 90 : Relatively Weak Middle Zone • Important: These are only ROUGH guidelines, based on RSA Experience Only!
Lower Layer Index (LLI) • Evaluates Lower Pavement Zone Stiffness • Typically Upper Subgrade • LLI = D600 – D900 • LLI < 25 micron : Relatively Stiff Lower Zone • 25 < LLI < 30 micron : Medium Stiff Lower Zone • LLI > 30 : Relatively Weak Lower Zone • Important: These are only ROUGH guidelines, based on RSA Experience Only!
Impulse Load Base Subbase Subgrade
FWD vs MDD deflections • 10 FWD blows per MDD 4 & 12 • 3 Drops: 1 seating, 1 40kN, 1 50kN • Done on AC directly onto MDD topcap • Time history of FWD drops recorded • MDD data recording density: 1 data point every 1 milli second (1/1000 sec)
