MSE Wall Repair

[foreng]

Looking for any viable options to repair an aging MSE wall (20+ years old) with severe corrosion of the internal strapping. Someone suggested drilled soil nails with a shotcrete face as an option. The wall has a wire mesh facing and is about 20 m high. The wall will have to overcome large surcharge loads (400 ton) from mining trucks as they back onto it. Trying to find an alternative to completely replacing it.

 

[cntw1953]

Instead of soil nail and shotcrete, how about soil nail and concrete crib wall, which would act like continuous beams over soil nail supports. It would cost a lot more then.

 

[hokie66]

I like the soil nail and shotcrete approach.

 

[oldestguy]

if this is granular backfill, how about injecting some stabilizing process to, in effect, "solidify" the backfill?

 

[InDepth]

Soil nail option sounds good. I think you also need to ask the question: What is causing the corrosion? Are the soils highly corrosive. If so, need to start thinking about corrosion protection and possibly soil mitigation (depending on the reasons)

 

[InDepth]

Oh....also call Soil Nail Launcher. This could be a perfect solution that is quicker than your typical soil nail wall.

http://www.soilnaillauncher.com/

http://www.soilnaillauncher.com/SNL/Other/contact.html

 

[foreng]

The wall was originally designed for 10 years but has been in service for 18 years. Another 4 years is required prior to demolition. This is why the original design was un-galvanized. The solidifying backfill idea is interesting what would that involve? I have one section of the wall that will have a concrete approach slab installed on top of the wall. I was wondering if that section of the wall could be stabilized by driving a series piles through the wall to bearing stratum, and pour the re-enforced slab on top similar to a pile supported grade beam.

 

[MSEMan]

Problem with the soil nail launcher will be the depth of nail. For a 20m wall you'd need at least a 12m nail and the launcher only really goes to about 6m. So your looking at drilled nails or tie backs.

There is no reason to shotcrete the facing unless you have corrosion issues on the facing. If you plate the heads of the nails and put them in at about 5' centers you can span between the nails with the facing you already have.

 

[fattdad]

We fixed a failed SRW using pilasters on 8-ft centers (vertical concrete columns) and tie-backs. We used helical tiebacks. Important to consider is where the helical tieback is deriving its capacity. Is it really appropriate for the helicie to get its capacity in what would be the reinforced zone of the SRW? I didn't think so, so I set a minimum embedment length for the tiebacks.

f-d

¡papá gordo ain’t no madre flaca!

 

[foreng]

Fattdad,

The pilaster and tie back system is interesting, what would be a good reference in order to see what the system looks like. Are the pilasters tied to each other somehow? How wide are the pilasters in general? The wall is 13m high (update from original post) and 100 m long.

 

[fattdad]

No reference to provide. We just designed the fix and built it.

The first thing we did was assume that the safety factor was unity (we had signs of failure). We then calculated what supplemental buttress would be needed (on a unit foot basis) to increase the safety factor to 1.5 (understanding the mode of failure and the concern on global, internal and external failures). We then considered the spacing of the pilaster (i.e., 8 ft) and determined the lateral load that would act on the pilaster. At that point it's a structural beam that's vertical, if you get my point. You have to consider bending moments, point reactions (i.e., at the tieback) and structual reinforcement. Each pilaster has a footing to support the weight of the pilaster and also the vertical contribution from the battered tie-back.

We used cast-in-place construction. We ruled out pre-cast construction as the intimate contact between the pilaster and the wall would still require some grouting or such.

f-d

¡papá gordo ain’t no madre flaca!

 

[cntw1953]

fattdad:

How the soil in between the pilasters is supported (what mechanism hold it up)?

 

[foreng]

fattdad:

Thank you for the information.

 

[fattdad]

re: soil mechanism to hold up soil between pilasters.

Arching.

f-d

¡papá gordo ain’t no madre flaca!

 

[cntw1953]

Yes, arching, that's one area I would like to learn more about. any practical reference? Thanks.