SOE Design Requirements 2

[LUGuy]

Are there any means to quantify the effects of vibration on an SOE system?

A contractor installed an SOE wall approximately 10ft deep less than 2ft from an existing masonry building on a spread footing. The SOE wall was made from drilling 8" pipes into the ground and sliding steel plates behind them while excavating. The adjacent building was relatively stable until they started driving piles 60-80 ft away. At that time, the foundation dropped at least 1" and moved away from the building 1/2" or so, all during two days of pile driving.

There is no question that the SOE failed and that the building foundation has failed. I am wondering if there could have been any way to figure on the effects of pile driving so close by. All visible excavated ground is sand.

I can't imagine that this system was in fact engineered. If it was, the engineer has also failed. Are there any code/OSHA/typical requirements to engineer SOE systems over a certain depth?

Miscmetals

 

[PEinc]

Relatively stable???? The pile driving vibrations were only the "straw that broke the camel's back." Usually, when excavating immediately next to and below an adjacent structure, the structure is underpinned or a very stiff SOE all is constructed. Drilled-in, 8" diameter piles with slid-in steel plate lagging does not, in my estimation, constitute either underpinning or a stiff SOE wall. A rough estimation is that you can experience about twice as much settlement as you get in lateral movement. Therefore, your 1" settlement for 1/2" lateral pile movement is about right. Cantilevered soldier beams do deflect laterally. That's why they shouldn't be used to support buildings.

Questions to consider:
1. How deep are the existing footings below the top of the 10' high SOE wall?
2. How high above subgrade is the botton of footing?
3. How far away from the SOE wall are the edges of the existing footings?
4. What is the footing load and what is the floor load inside the lowest floor level?
5. Were the pipe soldier beams set and concreted into larger diameter holes?
6. Was the SOE wall braced or tiedback? If so, at what elevation relative to the bottom of footings?
7. Was the building monitored from start of SOE wall construction? When did movement really start?
8. What are the soil and ground water conditions?
9. When the steel plate lagging was installed, was the dirt behind it tight against the plates? If not, then the dirt under the building had to fail before the earth and surcharge loads could be transferred to the soldier beams which then would also deflect laterally causing more settlement.

Sometimes, a poor design can be the problem. Sometimes, the SOE method is inappropriate. Sometimes, poor construction is the problem. Sometimes, the field conditions are not as expected. We don't have enough information to determine which factor or combination of factors caused the building to move. However, I'd bet that there are several contributing factors and guilty parties involved. Sorry.

 

[Focht3]

Much of [blue]PEinc[/blue]'s post is correct, but The cantilever portion leaves an incorrect impression: cantilever walls, if stiff enough and properly designed, are quite suitable for excavation retention for excavations less than 25 feet deep. It has been done quite successfully many, many times. I had one (in about 1995) that was within a few feet of an historic building. We monitored it for movement with inclinometers - less than 0.01 inch of deflection over a 5 month period. Bracing and tiebacks were out of the question. No damage claim.

As [blue]PEinc[/blue] will undoubtedly (and correctly) point out, those were quite stiff, strong walls - a far cry from the 8 inch pipe piles and steel sheeting described in the original post of this thread...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[LUGuy]

The contractor's response to my harsh criticisms was that he will have an engineer prepare a calc within a couple of days. I can't wait to see this one... Knowing that the building's foundation and SOE support has already failed, how could any engineer stamp a calc saying that it is acceptable?

And I did find OSHA standard 1926.652 which governs the requirement for design of SOE systems.

thanks,
miscmetals