Shoring for Masony Wall While Backfilling

[golind]

Can anyone recommend a book(s) that deal with the temporary shoring of reinforced masonry walls while back filling against them? The masonry wall, on the access ramp to the first floor of a multistory car park retains earth will which will form the base to which the rc slab on grade ramp to the first floor will be cast. The masonry wall varies in height from 3ft to 14 ft and has a total length of about 120ft.

 

[oldestguy]

If it is designed as a retaining wall to carry earth and surcharge loadings, you should not have to brace it when backfilling, other than having the final fill in front. I'd check what design pressure it is designed for, since compacting the fill to support a pavement may over-stress at-rest pressure in use. In that case, even bracing while compacting won't cure the later in-use problems of under design. Compacting can easily increase pressure above the passive values.

 

[hokie66]

I think oldestguy's comments refer to a cantilevered retaining wall. If your wall is a basement wall, braced by the structure above, you will have to either build the structure which braces the wall, or temporarily brace it. It is preferable, and less costly, to build the permanent structure first, then after it achieves the required strength, do your backfilling.

 

[oldestguy]

Assuming this wall is not part of a building basement wall, but a self supp porting wall, you might minimize the wall pressure due to compacting plus handle the slab design to account. What you can do to lower pressures during construction is keep compactors at lest 2 feet from the wall and design for active pressure plus surcharge. However, that uncompacted zone along side the wall must be spanned by the slab. So it has to have reinforcing to allow cantilevering over that near wall fill. My measurements of wall pressures where the two feet non-compacted zone is so built shows active or at-rest pressure is all that develops from the fill nearby. I liken that uncompacted zone as similar to the pressures in a silo (silo affect) due to loose soil hanging up on the wall and the nearby compacted zone.

 

[bimr]

Here is an outline for masonry structures.

Have you considered using concrete?

http://imiweb.org/ftp/Blogs/National/IMIInternalBracingGuide.pdf

 

[golind]

The wall is actually a propped cantilever and as the reinforcement from the wall ties into the slab on compacted grade which serves as the access ramp to the first level. The issue is the designer calls for the reinforced masonry wall( up to 14ft high) to be shored until the slab reaches design strength, and we have to compact the earth behind the wall before casting the slab. Would a timber frame bracing be economic.The wall has a total length of 140 ft? Would could other options be that as the wall has architectural aesthetic features so pockets and holes let behind are not acceptable.

 

[oldestguy]

Before going further find out what soil and surcharge pressures the wall is designed for, such as at-rest, active or passive and of course then the loads on the wall as a result. Then, you can compute loads into any bracing. If you don't follow my advice as to a loose zone left next to the wall, you must then assume conservative loadings in excess of passive pressure loadings due to that compaction work. Lacking any input from designer, I'd double the passive pressure loadings for the temporary bracing. For ordinary earth backfill this could be as high as 600 pcf equivalent fluid, certainly at least 300 pcf. How much pressure remains after the backfilling is done also needs to be known Then be sure the designer knows that question is still there. After that step, you can design the bracing.

As to type of bracing, others here may have advice. Be sure to consider the forces on the supports for your bracing and the allowable lateral earth pressure there. It is not the same as for vertical loads, very likely.

The assumed cost saving using the reinforced masonry may well not be there because of all the grief of holding the wall when filling behind it. Reconsidering the overall design might change this whole affair.

I would hope my use of the word "backfilling" is not confusing, because it really is just "filling". Force of habit.

 

[bimr]

You could use a concrete wall with brick veneer.

Perhaps you could post a sketch of what your project looks like.

 

[golind]

Thanks for all the advice.

 

[hokie66]

Bracing is going to be a big pain on this wall. It would be much simpler and more economical to redesign the wall to span from basement to first level, and delay the backfilling for the ramp until the first level provides the required bracing.