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Unformatted text preview: 73 6000
Velocity 3000 P - ZV 2000 1000 0
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 -1000 -2000
Time (s) Figure 7-2. Typical Force, Velocity and Double Wave up Traces from PDA. In order to determine the time at which the pile tip reflection arrives to the pile
top, the rise time must be considered. The rise time accounts for how fast the tip
reflection is developed and it will depend on how fast the hammer transmits the energy to
the pile top. The larger the rise time, the more difficult to have an estimate of the skin
capacity of the pile. Knowing the rise time allows us to determine the skin resistance at a
distance "x" from the top of the pile as x = L− RT
2c (7-4) 74
where L Length of Pile Below Gages c Wave Speed RT Rise Time Under this consideration all the skin capacity near the tip of the pile (length equals
RT/2c) can not be calculated. Figure 7-3 shows the plot of force minus velocity for the
same PDA signal presented in Figure 7-2 (i.e. double wave up). After that point in time
(point "b") the reflection from the tip begins to arrive. Figure 7-3. Procedure to Determine Tip to Skin Ratio for the Suggested Method From point "b" to a time equals 2L/c from the force peak (point “c”), both skin
and tip reflections interact creating an abrupt change in the force up trace. The decrease
in the force up trace shown in Figure 7-3 corresponds to the increase in velocity and ...
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This note was uploaded on 10/19/2011 for the course TTE 4004c taught by Professor Hass during the Spring '11 term at University of Florida.
- Spring '11