Retaing wall with temporary concrete blocks

[spockman]

I have been asked to review a segmental block retaining wall that was constructed about 10 years ago. The problem is that the contractor used unreinforced concrete blocks 2'x3x'x4' as the first course for his wall. We have tested the blocks and the concrete quality varies substantially, and in fact several of the blocks have started to fail due to freeze thaw. In my experience, these types of blocks are not intended for permanent use and will only continue to get worse. The wall is approximately 5ft tall and over 200ft long. I am trying to save the contractor from tearing down the wall and re-building but am not sure how to repair the block in place. Does any one have experience with this type of detail, any great ideas?

Thanks

 

[concretemasonry]

This certainly is an unusual design. What is composition and size of the blocks above the first course?

For the last 40 years or more, the various Segmental Retaining Wall (SRW) unit installation requirements called for the first course to be laid on a compacted soil base and NEVER on a concrete base. This applies for the same units internationally.

That is a general sign or indication of the importance of the base they are used on for the wall to perform as engineered. The strength requirements in ASTM are really there to maintain the strength of shear features molded into segmental retaining wall units. Normally there is no engineering required for SRW walls in the height range of 4' to 5', depending on the jurisdiction. The large walls (12" thick SRWs with various stepped heights up to 20' high and lengths greater than 500').

Is this wall just a gravity wall where the wall units are solid block with no provisions for shear resistance? The 2x3x4 solid units sound a lot like the Russian construction where the wall block are 1Mx1Mx2M used.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BAretired]

The best advice I can think of is to seal the blocks with a waterproof membrane on top, front and back. Good drainage between wall and earth is required as well. That will prevent the ingress of water but it is likely to be a temporary fix. Sooner or later the wall will need to be replaced.

BA

 

[BUGGAR]

These sound like "ecology blocks", usually cast from leftover (or non-spec?) concrete returned to the yard.

 

[oldestguy]

As Buggar comments, with concrete possibly with very high W/C ratio, what treatment would you do to a floor or roadway slab made from the same mix that is spalling? I'd think any treatment would cost more than replacing them. Can you hide it by attaching a facing layer of thin blocks, held via stainless anchor bolts?

 

[StrP88]

spockman (Structural)(OP),

Please provide several pics of the structure and damaged parts.
What material is stored their behind the retaining wall?

I had dealt with these in past.

 

[spockman]

I have attached some pictures from our recent site walk. The wall is at a condo development.

 

[bridgebuster]

The blocks are probably made from whatever concrete was left over in the trucks; that would account for the variation in quality and it's any easy way to dispose of unused concrete.

If the deterioration is resulting from freeze-thaw, you could chip away the bad concrete, dowel and place new concrete and apply a sealer. I say could because BAretired hit the nail on the head.

Is the wall leaning or does it look that way due to the camera angle? If it's leaning make the contractor rebuild it now. When the segmental blocks are removed you can better evaluate the mafia blocks and possible salvage them.

 

[StrP88]

spockman (Structural),

Total height including 2'x3x'x4'blocks is 5 feet or excluding?
How the wall above the block is attached to the blocks,do u have any information?
The two pics u attached are both on same side of wall or they each face of wall?
You mentioned that you have tested the blocks? What tests have been performed?

Are the base blocks on soil or slab on grade?
More pics can be helpful

I wont tear the wall down

 

[spockman]

It has already been agreed that the taller portion of wall will be taken apart an re-built. My concern is the lower portions of the wall, 5ft+/- on top of the blocks where the segmental portion is in decent shape.

There are no drawings for the original design, I doubt there is any connection between the blocks.

Pictures are from the same side, just grass lawn on high side with wood fence against wall.

Field cores were drilled and broken. Breaks came in between 1400 psi and 4000 psi. Clearly made from left over concrete.

 

[StrP88]

spockman (Structural)
So if they are tearing the top of the wall down why do you want to keep the bottom blocks in place which they are the cause of problem?

 

[dhengr]

Spockman:
Most of the problems with that wall are not going to go away until you do something to drain the water accumulating behind that wall. The uphill bldg. is draining its roof gutters onto the grade right above the wall. See the down spout in your last photo. This has to be controlled in some way. You can see water problems at every course of blk., and growing worse as you move down in elevation. Much of the 8x16 conc. blk. and the cap blk. can probably be salvaged, and reused. Some sort of draining fill behind the wall, with drain tile at the lower grade and weep pipes through the wall and out on the lower grade would seem in order.