Gravity retaining wall

[daciafelix]

I have encountered the following situation:

- a simple, rectangular, gravity ret. wall with backfill on one side.

- I was to calculate the safety factor against overturning.

Say heel corner is toward the backfill and toe is the opposite.

1. What corner shall I use as pivot for moment calcs?

Results are given for both situationsivot at heel and pivot at toe.

2. Which one is correct?

Speciality book mentions "either the base of the heel or the base of the toe can be chosen as pivot point, with a common use of distances from toe".

3. If pivot is taken from heel, what is Resisting Moment made of? Looks like the weight of wall rotates same way as lateral earth pressure.
Thank you.

 

[ToadJones]

I'd say do your calc from the toe....imagine trying to push the wall & footing over, it would rotate about the toe.

 

[daciafelix]

Thank you TJ. That's what any normal person would do. Problem is, I'm puzzled by the book explanation. How can be done the other way? Taking moment arms from the heel...how does this work?

 

[ToadJones]

maybe scan and post the pages for me to look at?
Or make a sketch and post it??

 

[InDepth]

It doesn't matter which point you takethe the moments about as long as the resisting moment is greater than the overturning moment. Ie. Equilibrium of moments must be equal about any point