My CAPWAP® analysis is showing a “Shaft Quake” larger than the “Toe Quake”. Is that possible?

It is generally unusual for QS to be larger than QT, but certainly not impossible. When the blow count is very large (very low set per blow), this means that the energy of the blow was not sufficient to activate all the resistance available on the pile, so the analysis is probably only showing the stiffness (defined by the mobilized resistance and quake), but not the ultimate capacity and quake of the toe element. QS can be larger than QT in such case. Another case where this could happen is with unplugged open ended pipe piles, where QS and QT are usually similar (the GRLWEAP recommended value is 2.5 mm – 0.1 inch for both QS and QT in this case).  Still another case is when the pile toe is on a hard rock.  So, although unusual, in actual practice it is possible for the skin quake to be slightly larger than the toe quake.

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