Can someone help me better understand "mobilization" of deep foundation capacities? 1

Primarily it is because the driving process has already mobilized the skin friction. Driven piles typically have a smaller cross section to use for end bearing resistance, it has some, but not much in comparison.

Drilled shaft is constructed in place, without movement to mobilize the skin friction.

Driven Piling overcome both skin-friction and end bearing during the driving process.
The driving process ends when the element has encountered sufficient bearing, side & end OR the depths are beyond the project budget.

A drilled pier can be placed under a number of criteria for length but seldom actually achieve significant end-bearing. A slight to significant amount of element movement is required to mobilized the side & then the end bearing, all dependent on the Geology and design criteria/assumptions. Under several circumstance, end bearing is never realized under 'working conditions'.

I would not say it is typical to only consider end or skin friction in drilled shafts. Maybe in US, but definitely not in the rest of the world based on the parts I have worked. Also i dont think skin friction has to "overcome" end bearing. It takes a small amount of movement to mobilise skin friction, contrary to emmgjlds comment. There are mobilisation graphs which show something like 0.5-1% of mobilisation is required.

There is generally no standardized way of designing piles when it comes to considering the contribution of skin friction and end bearing.

Some people account for skin friction and full end bearing capacity. Everyone knows that you need to move anywhere between 5-10% of diameter or even higher when it comes to end bearing. I worked with a guy who said that 9/10 we are very very conservative when it comes to pile capacity. As such, considering full end bearing was his way of reducing conservativism. Is there better ways of reducing conservatism, of course there is. But you try convince a reviewer to use fos of 2 instead of 3 (with out pile test data), aint gonna happen. He had done hundreds of pile designs and failed very few piles. The last job i worked on with him was for 2.5m diamter piles supporting 400m sky scraper. We got the job because the original designer was specifying something like 80m long piles. He said we could half that, and we did, and he proved it with test piles!

Other people use full skin friction and maybe 10-20% of end bearing capacity to account for the large mobilization.

Other people use full skin friction and no end bearing. Its more common in bored piles as there can be issues with base cleaning which is a real thing. Obviously with driven piles there are no base cleaning issues. That could be one reason why you seen the design methodology in your area.

I agree with EireChCh. It is not unusual to consider both skin friction and end bearing for the design of drilled shafts.

Jomaa Ben Hassine, PE
President
Civil Renewables, Inc.