Passive pressure for a retaining wall + expansion joint

[structural87]

1 - When dealing with the design of a retaining wall, why some engineers prefer not to mobilize all the passive pressure ? Is there any rule or it is just a way to be conservative ?

2 - if the retaining wall is long enough in plan and an expansion joint is introduced every interval, does the expansion need also to be in the foundation ? A shrinkage strip will delay the construction so 2 remaining choices : expansion joint, or additional reinforcement to catter for shrinkage effects ?

Thank you

 

[bridgebuster]

Typically, I ignore passive pressure to be conservative.

NYSDOT places contraction joints in the stem every 30' and an expansion joint through the stem and footing every 90'. I've gone a further with the expansion - a little over. 100' feet - with no ill effects.

 

[SteelPE]

1) I try to ignore the passive pressure. If I use it I will ignore the top foot or so. As bridge buster states, engineers do it to be slightly conservative.