In a given soil, the lateral effect of overburden pressure is constant with depth, as in $p=qk$, where:

• $p$: lateral pressure effect,
• $q$: overburden pressure
• $k$: soil lateral pressure coefficient.

Then, the effect of this overburden pressure on pile skin resistance will be constant or it would vary with depth? I read somewhere that it varies with depth. If the lateral effect is constant as I wrote above, why does its effect on skin friction vary with depth? Or it doesn't?