Cracked footing and settlement from earthquake.

[DeanSullivan]

Last year my friend was sitting in his house and heard a loud bang, he thought a car crashed into the house (it didn't). I told him that we had a small earthquake which is rare as we live 25 mile west of Chicago.

After a few months he noticed staircase cracking on an exterior brick wall in the southeast corner. Last weeked he discovered a cracked footing several feet north of the southeast corner and a gap between the footing and the stem wall. The gap is largest (3/4 inch) at the southeast corner and propigates 10 feet north and 3 feet west from this corner.

I heard homeowners are having foundation problems due to the drought this year which caused clays to dry shrink. Also, he had an addition put on the the north side of the house about 15 years back and I am wondering if this could be a factor too. I suggested that he hire a geotechnical engineer to do a subsurface assessment and to give recommendations for how to fix the problem.

My questions are:

Does he need a professional engineer or can he just get a contractor to fix the problem?
If so what kind of professional does he need, a geotechnical engineer, structural engineer or something else?
What scope of the work should he look for in engineering assessment what is the ballpark cost?
Lastly, what does something like this this cost to fix 5-10K, 10-25K or 25K+?

 

[jayrod12]

It all depends on what the actual problem is, what can be reused and what needs to be replaced. Without sketches and pictures I doubt anyone on this board would even venture a guess at costing.

There's a good chance he'll definately require a structural engineer and it is good practice to also hire a geotechnical to give the structural guys the proper design parameters.

Most jurisdictions will require sealed drawings specifying the fixes required at a minimum.

 

[oldestguy]

I disagree with Jayrod. This probably is a soil problem. In Wisconsin we are in a drought as I think Chicago is. It is not something to depend on a contractor for until the geotech has examined the soil there. Shrinkage is a very likelihood problem. In his review, if there is a structural problem, then that will be noted and structural engineer can be notified. I've seen many a settlement caused by clay shrinking in the midwest. If there are any trees nearby, they also may likely be aggravating the situation taking water out. In such a case, we have corrected the situation by watering the tree. Maybe removal also is in the picture.

 

[DeanSullivan]

Thanks for the input I wanted to report back with some answers to my questions. I called a reputable foundation contractor today and he said they would want a soils report before giving their proposal but he did say 30K was his ballpark cost for this type of job but of course its site specific. He also noted that his company is in the high end of pricing. I also spoke with a few geotechnical firms and the general concensus was to do two borings to 25 feet, one on each side of the corner that's settling. The scope of work included, boring layout/site access visit, reporting and recommendations, drilling and soils lab tests. Im assuming the lab would include soil classification, bearing capacity, atterberg, organic content and moisture but I didn't get that specific am I missing some thing? The geotech price was range for that scope of work was consistently arround 3-4k. I can see the value in having a structural engineer if that indeed is necessary. In this case I would venture a guess that starting with a soils report is the logical thing as jayrod said the structural would rely on the geos findings. Oldestguy your input was very helpful there is a tree near that corner and water is cheap! Its worth a shot. One suggestion I heard from my pal in CMT was to put some crack monitors in a couple places and watch it for 6 months to see if its still moving. I thought that was a good suggestion and for a cost of $20-100 it can't hurt. Finally I'd like to point out that the reputable engineering firms and contractors seemed uninterested, unwilling or at least unenthusiastic about doing work on a residential home, to the point of being rude and dismissive. With this said its no wonder there are one stop shop second rate contractor/quasiengineering firms gobbling up the residential market. Also explains why homeowners dont see the value in hiring a third party engineer.

 

[oldestguy]

I will put forth something that he may try. First off, look closely at the ground surface, where the grass may be short or where there is no grass, as along side walkways. If this is a clay of moderate to high shrink-swell potential and if rain has not fallen recently you may see cracks. The clay shrinks in all directions and it may show some opening between the ground and the wall. That observation should be enough to tell you what the problem is. Thus, no need for more borings, etc. If nothing shows, take a post hole digger and dig down a ways and see what you find. If this is pretty hard digging and dry or very low moisture soil, that also is sufficient. Now that you have confirmed the soil is clay and shrinking, no amount of structural investigation would tell you this. I am really surprised at what watering will do in these cases. For example at a nursing home in Iowa on the banks of the Mississippi (weathered loess soil) I visited with a friend there and noted two rooms were not being used. The walls has settled and cracked badly, floors were down. Outside in the yard was a big tree. A geotech firm was being contacted and I suggested some soil tests to run. I also noted how watering the tree might bring things up. A year later I was back again with the friend and noted the rooms were occupied. I asked the manager what the geotech firm did. He said they were not hired, but instead he tried watering the tree. It did the job. So, he planned to watch for that depending on seasons as to watering. I shudda charged him a fee, Ha.

So, you certainly can't hurt anything by watering, and it may take a lot of time, due to the low permeability of the clay and very likely deep drying effects. However, cracking can go deep but that would be a flow path at least until they close up. This has worked in other places, but removing the tree can make the improvement more permanent. After a year or so, you might have to patch cracks. I would not do so now. The monitoring of cracks is easy. Draw a line across the crack and make a slash on each side 2.0 inches apart. Then record the distance between them and the offset, if any with time.

If you have access to a builder's level or a transit, set some stakes in the ground. Record the elevations of them with time. The bench mark or reference should be something that is far away from the tree and less likely to be affected. A hydrant may be suitable, but even that can be affected by deep drying. Also do same for the affected foundation. Knowing the movements, if any will help.

I'd be less likely to recommend underpinning, etc. until this watering is tried for a few months at the least..

Other reasons for settlement could be cinders under the footing or peat, etc., in which case water would do nothing.

 

[DeanSullivan]

That story makes me hopefull, "Just add water". In that situation after one year with watering, did the soils actually rebound and push the foundation back up? I ask because my friend has a 3/4 in gap between the footing and stem wall at the corner and if im understanding correctly that gap may decrease or go away once the clay is rehydrated. So if he does raise the foundation in that corner now, while the clay is dry, could that result in upheval later as clays swell?

Has anyone seen a case where foundation was raised while soils were dry, then pushed up too far after the soils rebounded?
What is greater the down force of the foundation or the up force of the swelling soil?

I need to correct something from my original post, the earthquake was 5 years ago not one and the differential settlement wasnt observed untill this year. I think earthquake can be eliminated as the cause of the settlement/damage leaving dry soils as the most plausible cause. The house is 30 years old, in my judgement (im no geotech) settlement would have occured already if the cause was low bearing capacity/cinder/organic soils, right?

I just spoke with the my friend and suggested he try watering (thanks oldestguy). He is afraid waiting may lead to more structural damage. He seems determined to hire a contractor to fix this now, he's not going to try watering for fear of waiting nor hire a geotech due to cost. The plot thickens...Ill keep posting as the story unfolds.

On another note: I have a friend who is an arborist and I will give him a call and get his perspective on the subject and share the story from oldestguy. It demonstrates the importance of being interdisciplinary in ones approach to understanding and solving a problem.

 

[oldestguy]

As to raising back up to the original elevation, Yes it did, walls and inside slabs.. That happened not only there but at two other sites that I went back to. There may have been more that worked that way. One was a brick high school auditorium. The cracks in those high walls closed almost all the way, but some loose mortar, etc. kept them from getting all the way shut. The school's solution was not to cut down the trees, but dig a small trench alongside the wall and let water run in there all summer, each summer. That did the trick. Incidentally before I got on the scene, a contractor had underpinned one section (fortunately it was a trial section) and he remarked how hard the ground was and couldn't explain why the footing settled.

3/4" openings are not unusual. That nursing home job had settlements of about 2 inches, roughly. I didn't do any measuring, but it was so bad that they could not use the rooms. That soil was an area of weathered loess. Some other sites I have been at are lake clay sites, usually red color if that means anything. Mineralogy at times is montmorillonite.

What can a contractor do? Maybe underpin the footings, or put in new ones, or jack up the walls. Then, when more moist times come along, up go the foundations to elevations higher than when they were first done. Then be prepared to underpin the non-heaved footings to "catch up". So, if you get the house back up to where it was before, be prepared for it to some day raise up as much as it settled due to drying. Then new cracks open up reflecting that new differential heaving. So at this time, assuming the owner gets a contractor in, I'd back away from it and let him do his thing. He will be Damn sorry, I bet.

In my post about "95% compaction, it was a college classroom building where water was fed to that compacted clay by roof drain water that entered via backfill to plumbing trenches. Luckily the columns were set 5 feet lower and they didn't get moved near as much as interior floors and walls. Doors would not close, blackboard walls has the chalk trays and the blackboards looking like an arch across the room. In order to get that 95% a lot of drying was done. That town in eastern Wisconsin is plagued with plenty of shrinkage drying problems. We (our firm techs) sure learned a big lesson about not overly compacting clays.

In my experience, more often than not, nearby trees are present at these sites. I have not seen a site where the building raised up after construction, but I suppose it could happen, if you build on dry soils in drought times.

There are ways to cut down the high plasticity of soils, such as injecting hydrated lime, but that takes contractors experienced in that (Texas).

 

[jayrod12]

The only reason I say a structural is required is because where we are here anytime you need to repair or replace a structural component of a house foundation you need sealed structural drawings.

 

[a2mfk]

Oldestguy is putting you on the right track. I am a structural engineer at a company that also does geology and geotech. We deal with lots of soil problems including shrink/swell clays in Florida.

I don't know anything about the geology in your area and where your seasonal water table normally is, but I don't know why you would need (2) 25' deep borings. We would do a couple of hand augers to 10' in most instances if we thought we were dealing with plastic soils. Then they can run some Atterbergs on those samples to see how plastic they are. This is not that expensive (should be less than $1k).

They use wetting systems in more arid regions of Texas to maintain a moisture content. We have recommended this as a possible (and nearly free) solution to expanding the soils and you can get very appreciable lift. I think it usually involves a soaker type or drip irrigation system that delivers very small amounts of water but continuously. I have also heard of methods that use augered vertical holes that are then cased with perforated pipes, maybe down 5-10 ft, and the water is delivered deeper this way to ensure the clay layers get penetrated and moisture is increased throughout the upper 10 ft. Otherwise, you can wet the surface clays and these swell and then a surface moisture barrier- so you do not get good water penetration of the deeper soils. Unfortunately these are not exact, engineered solutions, and end up being somewhat trial and error, though relatively cheap.

If it is my house, I would start with a soil test. If it has a high plasticity index, like OG said you know your problem. I would then start with a soaker or drip hose and monitor the cracks widths for changes.

A structural engineer may be required only to evaluate the damage to the walls and recommend repairs.