Existing Timber Crib Walls

[joeskin]

I am working on a very complex wall design to replace an existing tiered timber crib wall system. The bottom wall has deteriorated. The upper wall looks as if it was recently replaced by the neighboring property owner. There is limited room to work. The upper wall retains a parking lot and is 22' above the bottom of the lower wall with a horizontal length of 15'. Town is after lower wall owner to replace wall (my client).

Wall is too high to install gravity wall system, (Recon or Redi-Rock) unless tie walls are left in place.

Here's the question can the existing cribbing be left in place? If so what steps can be taken to preventdeterioration and eventual voids behind the wall.

This is a cry for HELP!

Joe

 

[PEinc]

Could you drill-in or drive steel soldier beams in front of the lower crib wall at about 8' on center, then stack precast concrete lagging panels between the beams, then backfill the space between the back of the concrete panels and the front of the crib wall with clean crushed stone?

Or, could you soil nail and shotcrete the lower crib wall after attaching a drainage geo-composite to the front of the crib?

 

[joeskin]

Both great ideas. Thanks. There is room for this, as well as the construction of a large block wall to a max height of 10'. My one concern is the deterioration of the existing ties and the creation of voids over time.

From your response, I'm assuming you have experience with leaving the ties in place.

Any other info would be great, since i need to "sell" it to the code official.

Thanks again!

Joe

 

[MSEMan]

I would also look at the possibility of soil nailing the existing structure and putting on either a CIP, precast or shotcrete facing. This may be more economical than a cantilever soldier pile structure. Timber crib sounds like you may be in CA?

I wouldn't worry too much about the deterioration of the timber ties, it's not as though the timber is going to vanish, and the exposed timbers may be significantly worse than those buried in the fill. You can probably reduce the deterioration by providing proper drainage to the structure.

 

[PEinc]

There should be no problem with leaving the ties in place. That's no different than leaving timber lagging behind a permanent soldier beam wall. In addition, your ties should have been pressure treated. The wood can deteriorate, but it doesn't disappear or create voids.

As I already mentioned, you could soil nail the wall but you would need a specialty contractor to drill, nail, grout, and shotcrete. However, any dummy can drive or drill in soldier beams, nail on geocomposite drains, stack precast concrete or pressure treated timber lagging, and backfill between the lagging and the old wall. If the job is small, you may not find someone who is interested in doing the soil nail option.

 

[PEinc]

P.S. What is the height of the lower tier wall that has to be repaired?

 

[joeskin]

Thanks again to both of you. I feel the same about leaving the ties in place and with proper drainage it should not create problems. Sometimes it's hard to convince code officials.

MSEman - The is actually in northern New Jersey.

There is approximately 5' of clearance from the existing building to the lower wall and the lower wall is approximately 8'high. The upper crib wall is approx 12' high and starts 5' feet behind it.

Also, since this system is in an urban area, the fill is loaded with misc debris.

Just another day in the office!

Joe

 

[PEinc]

Bad news. If you have only 5' of clearance between the building and the lower wall, you will have a hard time installing soldier beams or using any kind of equipment in front of the lower wall. If you could drive soldier beams from behind the upper wall, you might be able to get the beams into the narrow space. However, you would be installing beams very close to the existing building which could cause some problems due to noise and/or vibrations.

With only 5' of room to work in, you also would have problems installing soil nails. It may be possible to build a gravity block wall with minimum embedment below OG. However, you would need large blocks without geogrids and you may have to design for large sliding and overturning forces from the upper tier wall(s). You might have to excavate by hand and you may need to set the blocks using a crane sitting behind the top of the upper wall if you can't reach from the ends of the building. Good luck with that one.

 

[MSEMan]

Here's an idea - not sure if my assumptions are correct but - most crib walls I've been associated with are backfilled with fairly open graded stone. Behind the cribs are usually backfilled with unclassified. If this is the case in your situation, you could grout the whole mass together - ties open graded backfill and all. It isn't a very elegant solution but it ought to work and minimixe disruption to the existing conditions. What you'd end up with is a mass concrete wall at the toe of your slope instead of a crib wall. If you needed to contain the grout you could drive temporary sheet piles behind the crib wall.