Retaining wall bearing - inclined load and horizontally restricted base

[Andrew88]

Hello everyone,

Please have a look at the attached file.

The resultant forces and bending moment have been calculated around the point A. To counter sliding from horizontal force the wall has been tied to existing slab.

In the bearing capacity (drained conditions) equation as per EC-7 (and not only) one of the 3-terms has a load inclination factor, which is a function of horinzontal/vertical force. Can I assume that because horizontal movement of the base (toe) is blocked my resultant load acting on the eccentricity "e" will have only vertical component as per situation 2 or do I need to consider it as situation 1? The Bowles states that if the friction angle is zero, sliding occurs and bearing capacity is zero (only the base width term considered) so if I have no sliding at all it means the bearing capacity is 100% and no load inclination occurs? Is my deduction correct?

Thank you,
Jed

 

[oldestguy]

We don't do design here, but try to give any advice. The info needs to be complete. What is there is very incomplete. What are you retaining and its properties? What sort of pressure diagram are you using to show the effect of that retained load? Any slope to the fill? Any surcharges? What is this wall sitting on as to properties, etc. Dimensions also might help.

 

[Andrew88]

Thank you for the reply.

There is an existing 1.5m high diesel storage tank bund that has been built above ground using unreinforced brickwork. This will collapse once is full with water/diesel and needs strengthening. We want to do it by using precast L-shape panel that would be placed against existing bund wall and anchored to a new reinforced plinth. The cross section would be: brickwork-void for concrete-precast wall. The bund is coated on the inside and impermeable. Please see attached file and focus only on plan and section sketches. The moment Ma acts in opposite direction then noted there.

Unfortunately, I don't have data on soil so have to be conservative. If soft soil is encountered it will be definitely replaced with well compacted granular subbase to as deep level as necessary.

The sliding will be resisted by dowels that will connect old and new slab. Hence, I would welcome your advices on whether it is possible to disregard horizontal part of the resultant force acting on eccentricity for bearing capacity calculation as in my first post?


Jed

 

[oldestguy]

I'd look at enclosing the old tank with a new one with hoop type strength all around it. It may take a horizontal beam system to make sure the long wall is properly restrained. I'd not depend on tying to an old slab that may be cracked, weak, etc. Suppose the dowels pull out? Your whole design depends on that. This new wall certainly can be designed as a tank wall. I'd add that filling in the cavity between old and new wall with concrete can be a bad idea. That liquid concrete might have sufficient lateral pressure on the brick wall to cause it to collapse inward. some careful backfilling is stages may be required.

 

[BridgeSmith]

"Suppose the dowels pull out? Your whole design depends on that."

From our experience, pullout failure of dowels in tension is a very real possibility. Adhesive anchors can develop the full strength of the bar or rod, but only if the adhesive is mixed thoroughly and the holes are cleaned properly. One or the other fails to happen fairly often on our jobs, and we (the state DOT) have full time construction oversight personnel. We never rely on the tension capacity of post-installed bars or rods with adhesive anchors.

 

[Andrew88]

Thanks for great tips!

Yes, I considered to have concrete poured in about 400mm stages to prevent collapse from liquid pressure.

I have modeled 3 tie beams that are made of UNA 200x100x10. It is shown in the attached screenshot. This profile will be fixed with one bolt to each 1m wide L shape panel.

As tie beams resist hydrostatic load I am considering to have just a small 100mm plinth of the toe width on which the precast panels would be placed without anchoring them down. I am also willing to skip dowels as per your comments and to make the job easier.

Would you have any further advices to this approach?

Jed

 

[oldestguy]

"Now you are talking" as the phrase herein the USA says.

 

[EireChch]

@jedrzej88 - should your eccentricity "e" be measured from the centre of the footing, not the point A?

If the load is acting off centre from the footings centroid then the bearing area is reduced to an effective bearing area.