Retaining Wall Failure

[MAX-24-Dean]

I built walls in Charlotte. I can answer the question of "how close..." You can build the wall and building as close as the qualified engineer says you can build it, on an approved set of drawings, as long as you follow all the instructions he gives.
There is no acceptable rule of thumb!

Warning to many here. I see a lot of posts that have SOME knowledge. There is much more to this than the simple comments! A little bit of knowledge can be very dangerous

Fishdrivel, this is good information for everyone!!!
Can't be communicated enough, hire a Civil engineer to get a stamped set of drawings. Every project location has variables where "rules of thumb" might/will not work and get you into trouble.
I have seen a couple of projects that the company I was working for got the do over contract.
Be smart and don't injure or kill anyone with the "I think this will work mentality".

I don't know how many times I have seen contractors guess at this, because they can save the customer a lot of money by not having engineering fees. Only to find out they had to redo the retaining wall and get an engineered stamped drawing.

It cost a lot less to do it right than do it over, and it may safe a life.

 

[Realtornz]

I have always wondered why tall walls do not have rebar and concrete poured into the block plus lots of "dead men" View attachment 728667

If it is only about cost, it would have been cheaper to do it right the first time.

A picture is worth a 1000 words...tho I would expect to see weep or drainage holes at the base to allow water to flow from the backfill metal?

 

[fishdrivel]

I don't know if there is a fix for that wall other than taking it all out and starting over. How that ever passed an inspection is beyond me. How they ever got a permit to build the garage without documentation, including permits and inspections, of the supporting wall is beyond me.

Theoretically, the engineer could design a wall that is the same distance from the garage as the height of the wall including the underground portion.
Now moving it that far from the garage would still mean that the new wall would not be on the failure plane of the swimming pool that is in front of it. the garage would require shoring during construction.
I say theoretically because a smart engineer would walk away from this and not end up in a court battle as a defendant or a witness.
These cases get very ugly, with both sides bringing in their expert witnesses.
It could get very expensive and might include at the engineer's recommendation, to remove the garage, the wall and the pool!
You can imagine the expense when contractors figure out that it has to be done and that everybody with anything to do with the project will be looking for somebody to blame.
In my day, I walked away. I wanted nothing to do with these kind of legal problems. I had a long and successful career!
Best thing that could have happened is for the wall to have been built by the pool builder. They have a lot of insurance for reasons like this.

 

[Grumpycat]

I built walls in Charlotte. I can answer the question of "how close..." You can build the wall and building as close as the qualified engineer says you can build it, on an approved set of drawings, as long as you follow all the instructions he gives.
There is no acceptable rule of thumb!

Warning to many here. I see a lot of posts that have SOME knowledge. There is much more to this than the simple comments! A little bit of knowledge can be very dangerous!

42 years ago one of my engineering professors said, "All retaining walls will eventually fall. Soil is a fluid of high viscosity. Eventually the soil wins and floats the wall."

 

[3 Horse Ranch]

42 years ago one of my engineering professors said, "All retaining walls will eventually fall. Soil is a fluid of high viscosity. Eventually the soil wins and floats the wall."

Only true if there is inadequate drainage of water, inadequate tie back into the load and/or a bad foundation. In actuality Hoover, Grand Coulee, et al are retaining walls, I don't foresee them failing any time soon. The walls I've seen fail aren't because the wall floated on the soil. Either the toe kicks out or the wall rotates, but this is caused by an inadequate foundation, inadequate tie back into the soil, and inadequate drainage. The wall Muhammad posted failed because of inadequate drainage, the material behind the wall washed away and the wall fell because there was nothing to support the back lean of the wall. In the image Marhar posted there is no foundation and there is nothing to keep the toe of the wall from washing out and there is nothing to carry excess water away from the back of the wall.

 

[Grumpycat]

Only true if there is inadequate drainage of water, inadequate tie back into the load and/or a bad foundation. In actuality Hoover, Grand Coulee, et al are retaining walls, I don't foresee them failing any time soon. The walls I've seen fail aren't because the wall floated on the soil. Either the toe kicks out or the wall rotates, but this is caused by an inadequate foundation, inadequate tie back into the soil, and inadequate drainage. The wall Muhammad posted failed because of inadequate drainage, the material behind the wall washed away and the wall fell because there was nothing to support the back lean of the wall. In the image Marhar posted there is no foundation and there is nothing to keep the toe of the wall from washing out and there is nothing to carry excess water away from the back of the wall.

Right. So we should quit wasting our time and energy on inspecting dams because "(you) don't foresee them failing any time soon."

Toe kicked out, whatever, is all due to soil being a liquid even when it is dry.

The pictured wall failed because stacked blocks have little strength in tension. Was pressed from behind because soil is a liquid.

 

[fishdrivel]

42 years ago one of my engineering professors said, "All retaining walls will eventually fall. Soil is a fluid of high viscosity. Eventually the soil wins and floats the wall."

He is technically correct. Tht said, there are many walls that are hundreds of years old.
My warranty expires after 200 years!

 

[3 Horse Ranch]

Right. So we should quit wasting our time and energy on inspecting dams because "(you) don't foresee them failing any time soon."

Toe kicked out, whatever, is all due to soil being a liquid even when it is dry.

The pictured wall failed because stacked blocks have little strength in tension. Was pressed from behind because soil is a liquid.

It's all about drainage and tieback for an earth retaining wall. The base of the wall has to be kept from moving, that is accomplished by putting the base of the wall below the grade on a good foundation. If the ground slopes away from the wall, it requires the base to be buried deeper.
The wall above the base needs to be tied back into the soil several feet. We installed 4"or 6" perf drain pipe behind the wall and 3/4 crushed rock on top of the pipe behind the wall as well as filling the cavities of the wall block with the same rock. It isn't rocket science but it's nonsense to say that all walls will fail unless you are using infinity as a time frame.

 

[fishdrivel]

It's all about drainage and tieback for an earth retaining wall. The base of the wall has to be kept from moving, that is accomplished by putting the base of the wall below the grade on a good foundation. If the ground slopes away from the wall, it requires the base to be buried deeper.
The wall above the base needs to be tied back into the soil several feet. We installed 4"or 6" perf drain pipe behind the wall and 3/4 crushed rock on top of the pipe behind the wall as well as filling the cavities of the wall block with the same rock. It isn't rocket science but it's nonsense to say that all walls will fail unless you are using infinity as a time frame.

This is general information. How did you determine how far back to tie the wall? It sounds like you are using pre-engineering? How tall is "your wall? How did/do you determine "good foundation?"
Not trying to bust your chops but I have been trying to get across to posters about the dangers of not getting proper engineering.

It is not rocket science but it is science!

 

[bcp]

Being a soil scientist is a dirty job.

Bruce