Mobilized Soil Reaction in L-PIle

[dfranks]

I am NOT familiar with L-pile, but I have been shown a graph of "mobilized soil reaction vs. depth" for a large caisson.
The soil reaction is in lb/in.
Can someone explain to me in simple terms what this means?
I am used to dealing with psi or psf, such as that caused by active earth pressures, and this graph initially looks like a similar concept, but I think I am missing something.

Thanks