Investigative Engineering 1

[CAS1]

I posted another question on here before and at the advice of some of the people here, I have an appointment next month for a structural engineer to evaluate our crawlspace foundation.

During Hurricane Sandy, our foundation was damaged. A pre-existing hairline crack on the side of the house got larger, a second crack developed on the opposite side of the house, and the back of the house started to lean backwards by a couple of inches. The floors and sheetrock inside the house are cracked from it.

The engineer for the flood insurance company claimed that the damage was done by earth movement, which is not covered by flood insurance. Now that I've hired my own engineer, how would he go about investigating the true cause of the damage? Would it be relevant to him that we've had a prior flood with no damage? The other flood water was deeper but had no wind. During Sandy, there was wind with flooding but the flood wasn't as deep as the prior flood.

Is it possible for wind to damage a crawlspace foundation? Also, is it relevant that there was a flood vent right next to the damaged area of the foundation, but the flood vent was closed during the flood?

We had flood insurance for a stream that runs behind our house but that doesn't cause the flooding. The 3 storm drains in front of our house back up, and our house is lower than the other houses, so we get all the storm water in our yard when the drains clog.

Our engineer has to figure out if we need to continue to go after flood insurance for this, go after homeowners due to wind, or go after the township because of the drain issues. How will he be able to determine that?

 

[Ron]

CAS1....let's assume first that the engineer you hired is experienced in forensic processes for engineering and construction. Given that, there are usually relevant indications of the cause(s) of certain types of damage. Foundations are usually the last part of a structure to be directly affected by wind and without significant evidence of other wind damage, it isn't a likely suspect.

Rapidly flowing water at the surface or water that rises or falls quickly can damage a foundation. In sandy coastal plains soils such as yours, a sudden drop in the water level causes consolidation (compaction) of the soil which results in settlement. Rapidly flowing water can scour the foundation soils causing erosion and undermining of the footings.

The engineer will have to do a thorough visual assessment of the structure and determine the effect of soil and groundwater conditions and their condition changes on the structure. Lateral pressure of the flowing water on the structure should also be considered.

Good luck.

 

[StrucPatholgst]

A pre-existing, weathered crack in a foundation pretty much proves that you have some mode of pre-existing movement in your supporting soils. That the crack increased in width as a result of a storm event proves that the soil movement (consolidation, etc) is still an ongoing issue. Flood insurers typically only cover buoyancy effects, hydrodynamic effects, hydrostatic pressure effects, and scour effects. Consolidation of soils, subsidence, and differential movement are typically excluded in crystal clear language within the policy. Also, it would be pretty amazing if wind moved your foundation.

The correct type of engineer to hire is called a forensic structural engineer. Insurance companies usually hire independent, third party forensic engineering firms with years of flood experience to inspect properties, investigate damage, and determine damage modes and causes. I think it is highly likely that your insurer hired a third party forensic engineer. It would behoove you to to hire one as well, if you want a valid second opinion. But from what you've described, it would be difficult to prove a buoyancy, hydrostatic, hydrodynamic, or scour effect caused the damage you described to a crawlspace foundation, unless you were right on the beach and subject to coastal overwash or wave impacts.

 

[msquared48]

Seems to me that wind on a structure that is founded on very wet soil can encourage a vibratory action from vortex shedding that might cause a localized quick condition, depending on the soil of course, that would locally weaken the foundation.

Could be a stretch to prove though without the evidence of any sand boils.

Mike McCann
MMC Engineering

 

[CAS1]

Thank you all for your responses. I wasn't aware that I should be hiring a forensic engineer. I feel sort of bad for the person I've already hired, but if he's not the right person for the job, then it's better to change ahead of time.

I didn't see any mention of the first flood in any of your posts. Does that mean that the first (deeper) flood we had, without any damage, isn't relevant to this investigation? Wouldn't it be that if the soils were prone to movement that they would have moved then too? And to clarify, the original hairline crack is thought to be from when the house was built. We have lived in the house 10 years without any change in the crack.

I sort of believe that lateral pressure could have been a contributing cause. Like I said, the flood vent next to the crack was closed. In addition, that was the direction of the water flow. The water flowed from the street in front of the house, down the side of the house with the crack, and right around the area of the crack it changed directions towards the house.

We did have wind damage that took down a large tree in our front yard. The ground was saturated and with every wind gust, the tree began to lean. It took about a half hour of pounding wind before the tree fell down and the root ball was exposed. It took down some of our vinyl siding and tore up our roof too.

I'm not sure if any of the additional information I gave you is at all relevant, but I do appreciate your input while I wait on my appointment with the engineer.

 

[StrucPatholgst]

What is the propagation pattern for these two cracks? Vertical, horizontal?

 

[EngTipsUser18]

I agree with StrucPatholgst, as I used to work for a company like that doing that kind of work. Hire a Forensic structural engineer who is used to working with insurance companies, not all forensic engineers are used to working with insurance companies. you have to use the right words, there are hot button words that will hurt/help you. google structural engineer property loss consulting

 

[CAS1]

I'm sorry StrucPatholgst, I missed your post. The crack is vertical and follows the mortar joint on the side of the flood vent and then keeps going deeper into the crawl.

I was wondering how to tell if groundhogs were the problem. They keep burrowing under our shed and deck (even though we have 2 dogs to scare them away). I know homeowners insurance wouldn't cover that but I wonder if flood insurance would.

EngTipsUser18, care to elaborate on key words that could help get our claim paid? Thanks.