Retaining wall system 1

[geo321]

I have a retaining wall system which conisists in a small post spaced every 3 meters and in between 2 beams and blockwork system. Refer to the attached picture.
I need to verify the foundation dimensions.
 1- Is the post will carry the soil pressure supported by the blockwork according to its tributary width ?
2- if i want to include the passive earthpressure, it will result in a higher moment than the active since the kp is around 3 (ka=0.33)  and the height difference is small !!
Thank you for the help.

 

[oldestguy]

Is the block wall secured to the posts to carry any of the block weight?

 

[geo321]

No it is not

 

[jayrod12]

I would be inclined to say yes to oldest guy. The two concrete beams (1 at top and 1 at bottom) will tranfer all of the horizontal and vertical load directly into the posts. So you do have dead load helping the overturning case.

In response to your questions however,

1 - No, because the wall spans vertically and not horizontally you can not account for the post trib width. You could however account for the passive lateral pressures that go into each beam and apply 2 point loads to the post (This is also how I would be analyzing the active pressures as well).

2 - I'm not sure I follow, the moment cannot reverse direction due to passive pressures. Once force balance has been reached passive pressure no longer continues to develop. You need movement to enact passive and active pressures.

 

[oldestguy]

Regardless of the answer to the question, assuming the post is concrete reinforced and the footing is large enough, I suspect the joint of post to footing won't practically work as indicated in the dwg. Perhaps with some increased post depth, front to rear, maybe then.

 

[oldestguy]

OG here:

Been wondering if you might consider a different support system. Suppose you dug a trench parallel to the wall at each post location, roughly as long as it is deep (below your former footing grade). Sort of like a big flat spoon shape down there. Before there is cave in, drop in a reinforcing cage and immediately dump concrete. Then, before concrete has set, install the post. The amount of work needed is likely less than your plan. Also this deeper "footing" will have much better resistance to wall horizontal forces on the post. Being buried, who cares how neat its dimensions are. You could have the post held correctly before concreting, but stand a chance of cave in before concreting. No fancy backfilling needed either.

 

[oldestguy]

Guess the link didn't go. try again

 

[MrEngineerUS]

I've recently had to think about your passive v. active pressure question for a project myself. Basically, jayrod is correct. The both the passive and active pressures require movement of the wall to develop. Passive requires almost 10x the movement of active pressure development. Therefore, you have to use engineering judgement on if you structure can actually develop these pressures; otherwise, if no movement is expected, use the at-rest coefficient for both. In a case like yours, I think it would be adequate to use active as the driving pressure and at-rest as the resisting pressure. In reality the resisting pressure could be higher depending on your wall movement but this may help avoid that net passive pressure problem your having.

 

[geo321]

Sorry for the late message.
I will design it as per the following.
the 2 concrete beams will act as support for the horizontal triangular soil pressure. They will transfer their torsional moment to the post where the post and its foundation will be designed versus overturning.
Blockworks will be concreted and reinforcement placed into their holes. This reinforcement will be anchored into the bottom and top beams.

Any comments ?