I guess we say "half-cycle' because it does not finish the cycle.
Settlement is more like cold pull rather than a cyclic strain - it changes the bias on the stress state. And (where there are no nonlinear complications), the change in stress between the installed and operating states remains unchanged.
B31.1 paragraph 102.3.2(b)(2) calls this out as a separate stress evaluation for settlement with a limit of 3S.