Pre-cast Retaining Wall - Mass Concrete Base Design

[neilquane]

Hi all,

We've been tasked with the design of retaining structures utilising precast 'L-shaped' wall element.

Ordinarily I would specify the pre-cast elements to be dowelled in to an RC base designed to resist the overturning moments and sliding.

In this instance we have been asked to prepare a mass concrete base option for these structures.

My initial thoughts were the following.

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The pre-cast wall is dowelled in to the mass concrete​

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The overturning from the precast panel is resolved in to a tension force within the dowels in to the mass concrete​

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Sliding is resisted through shear transfer of the dowels​

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The resulting OM from the vertical and horizontal forces are resisted by the weight of the mass concrete foundation to achieve appropriate FOS​

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The sliding is resisted by base friction and passive resistance of the soils to achieve appropriate FOS​

I'd be grateful for any thoughts on the above.

Thanks

Neil

 

[EireChch]

Dont assume full passive resistance for sliding... ignore it or at least give a good factor of safety...

 

[neilquane]

Thanks EireChch,

Other than that does that approach seem reasonable?

Thanks

Neil

 

[IDS]

If you need tension ties at the back of the precast to prevent overturning then there will be significant bending moments in the base so it should be reinforced, not mass concrete.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[EireChch]

I have designed reinforced concrete retaining walls, but not precast walls dowled into an RC base. I will have a go regardless and some of the structys can correct me. Note, my opinion is based on my gut feel and nothing more...

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The pre-cast wall is dowelled in to the mass concrete
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The overturning from the precast panel is resolved in to a tension force within the dowels in to the mass concrete - I doubt practically you will get enough capacity in the dowels. Typically in an RC wall you have L bars that are lapped up the face and then returned back into the base. This is a good connection in my mind. But a number of dowels to resist overturning?? Not sure...May you can put enough deep dowels, at large diameter at close spacing but will this be practical. Also, is the overturning moment resolved into a tension force? I would think some portion of it will be but not a good chunk wont.
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Sliding is resisted through shear transfer of the dowels - sliding will be resisted by the base friction as you have said below. The pre cast panel will receive some shear force at the connection which will be transferred to the dowels. I think that should be easily achieved.
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The resulting OM from the vertical and horizontal forces are resisted by the weight of the mass concrete foundation to achieve appropriate FOS. The weight of the wall (stem and base) will resist overturning, but again will it be practical to rely on increasing the thickness of the the members to get the FOS. Increasing the heel length will give you more bang for your buck with the additional soil weight.
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The sliding is resisted by base friction and passive resistance of the soils to achieve appropriate FOS