Shoring Failure - Investigation Documents 4

[InDepth]

So I just got a shoring project where the wood lagging failed, soil dumped out, the soldier piles displaced, and the adjacent structure got damaged. (and subsequent emergency shoring was placed). The owner is having us work with his lawyer to perform an investigation. I've prepared a list of documents that the lawyer should obtain for our review (see attached). Is this list comprehensive enough?

Any experience are recommendations with shoring "failure" investigations, adjacent building damage claims, and construction insurance delay claims; would be greatly appreciated.

 

[PEinc]

Your list is very comprehensive. Lots of billable hours there! Did the lagging boards actually break or did they fall out from behind the soldier beam flanges?

I've designed and built a few thousand sheeting walls, the majority involving soldier beams and lagging. I can't say that I ever saw a lagging board fail. I've seen soldier beams move and the lagging fall out from behind the soldier beam flanges. I've seen loose fill fall from behind lagging and from around the soldier beams and the lagging then drop. I never saw a lagging board itself fail. If I were you, I'd look for soft soils behind the lagging, excessive soldier beam movements, and poor lagging installation procedures. If you have very soft soils, then the use of lagged soildier beams may have been a poor choice of wall type. Sheet piling may have been more appropriate.

In the Northeast, lagging is usually ungraded, mixed hardwoods, 3" minimum nominal thickness. Good luck trying to check the material specs. More important than the wood specs is the condition of the lagging boards. Was the wood new or used? Were there excessive splits in the wood? Were there excessive knots in the wood? What was the actual thickness of the lagging? How much bearing did the lagging boards have on the soldier beam flanges. Was the lagging installed tight to the excavated soil face?

 

[PEinc]

PS, if the soldier beams are not bearing against undisturbed, competent soils and are tiedback, the lagging boards can bulge and break when the tieback anchors are tested and the soldier beam moves backward - especially with soft or loose soils. However, this is not usally a big problem because, at that time, the excavation is not very far below the tieback grade and the lagging boards near the tieback anchor can be replaced.

 

[DRC1]

Bid documents
Design Calculations
Engineer/Owner correspondence.
Historical use of properties
Monitering wells and water level data, especially recent levels
Recent activity, especially on retatined property
Bid review documents with all bidders
Experience of shoring designer and review engineer
Experience of shoring contractor and tie back subcontractor
Any previous getechnical information for site or retained site
Material data for tie back components
Recent weather/ seismic history

As far as documents go its a fishing expedition, you never know which documents are going to be useful. However the first thing you should do is perform an independent design yourself. Not that this will decide if the orginal design was right or wrong, but you will understand what on this
site effects the performance of the design.

 

[BigH]

As PEInc indicated, it is a pretty exhaustive list. One of the things that you might wish to add is the "Owner's Requirements" - this might or might not be existing. I am thinking along the line as to what the serviceability tolerances were on the design of the excavation support - i.e., no more than 1 inch top deflection, etc. Given this, then one can tell whether the design requirement was met - if the design had a chance to "win."

I would also find out as much as you can about the existing structures nearby. When were they built, types of foundation, depth to foundation, any problems in their construction? Any problems during the service life up to the time that your project started? Estimated foundation loading. Has there been other similar problems in the general area of similar soils that have occured in the past? You might also need to do more soil testing - to find out certain soil properties that the prelim and design investigations didn't note - or think important; e.g., swelling potential of the clay - free swell and/or confined swell. Time of year might be important (in light with nearby trees?? - see Bozozuk on effects of trees on soil movements). Was all the required surveying done at the time of the work? I was once on a job and had these specs asking for the world - then when I started doing what I was required to do, they said - "Nobody ever does that!!" - the specs were to cover their arse but they didn't want to pay for it. Was there a specific survey plan/methodology developed for the project? The list could go on - but look to PEInc for your inspiration!

 

[InDepth]

Thanks PEInc, DRC1 and BigH for your valuable comments. Based on an offline interview with the superintendent, the lagging actually broke and split in bending rather than bowing and popping out (rumors until evidence is provided).

I'll update you guys on what I find out and we can learn from this.

It seems that reported cases of failures are becoming rare because the cases are settled out of court...and then the designer no longer can learn from and avoid these "failures".

 

[dik]

The type of soil can have a big influence on the type and magnitude of pressure distribution.

Also drainage issues can have a big impact.

DRC1 brought up a couple of good points regarding monitoring wells, etc for water level data; can consider installing pressure tubes.

Also try to pick up any and all geotechnical reports for the area, including the subject site.

Recent weather can also have a big impact. There may be 'amateur' weather stations in the area that have detailed weather information. Although these are not 'official' I have had info from these admitted in court. The Canadian weather information includes information from these amateurs.

You can also look into project specifications as well as drawings for materials, alternatives and/or ambiguities.

Dik

 

[dik]

May be helpful to get a surveyor involved and get detailed info about soil movement.

Dik

 

[chicopee]

Any chance of viewing pictures of the damaged project?

 

[InDepth]

With legal cases, has anyone had anyexperience with proprietary software, especially when you are trying to protect a shoring engineer? Here are my thoughts. How do you protect a company without compromising their internal software/calculations?

Software
1. Provide a list of Software and versions used in design (Shoring Engineer & Geotech Engineer). Provide Software manual.
2. If proprietary software is used, provide sample calculations that validate results (FHWA, Caltrans examples, etc).
3. If proprietary software is used, provide a design criteria or methodology that is used (references) by the software.

 

[DRC1]

Talk to the attorney for the side for which you are working. The answer will depend on the form of litigation and the state.

 

[fattdad]

Just remember, you're not the advocate. That's the job of the lawyer.

You may want to look at various contracts. To look at work product and feel something's missing may lead you down a faulty path. If it's not a part of the contracted work plan, then it's not missing, it wasn't included in the scope of work. Then again, if it's something that should have been in the scope of work (but wasn't) that's a different story.

As a structural engineer, you may be familiar with using typical values for steel strength, modulus and the like. In soils it's different. You need to see just how the geotechnical parameters were assigned. There's a liklihood that the geotechnical (or shoring contractor) used guess work. You may need to do a parametric exercize to see just how sensitive the guess work is to the final outcome (i.e., failure).

Good luck! These can be fun (and challenging) projects!

f-d

¡papá gordo ain’t no madre flaca!