Foundation Problem

[Clcrom]

Hello,
I have a foundation related problem that causes the floor to rise about 3/8 of an inch at one corner of a room in the winter. In the spring the problem gradually goes away and dissapears completely by early June. The movement is enough that for about 4 months of the year, the bathroom door won't close. I have checked the foundation under the house with a Laser level, and this confirms that the foundation raises up more than 1/4 inch.

Neither the foundation or the outside brick wall shows any signs of cracking. We live in the Dallas Texas area where the soil is very unstable black gumbo clay. To provide a a good stable foundation, piers which goes down to solid "white Rock" are strategically placed in the foundation. The foundations are well reinforced. In our particular area, the white rock is about 6 feet below the ground surface.

According to what I understand about the geology in this area, the white rock is very thick. So it appears unlikely that white rock does any moving. But part of my foundation clearly moves about 3/8 of an inch from summer time to winter time. Since neither the foundation or the brick wall on that side of the house has any cracking, it appears that the foundation must tilt slightly due to the seasonal changes.

So far, no one can explain to me what is causing the problem, much less propose a fix to the problem. I have one theory. Does anyone think that it is possible, that the unstable soil pushes the foundation up slightly so that the piers are raised slightly off the white rock? Since the foundation and also the piers are strongly linked with rebar, it appears unlikely that the foundation would be raised off the piers.

It may be that the temperature has nothing directly to do with the problem. In general, the soil expands greatly with water, so if the soil moisture content inreases in the winter months compared to the summer months, then, there could be quite a high lifting force on the foundation.

I would appreciate any suggestions that anyone of you may have. Thanks, CLcrom.

 

[ACtrafficengr]

Not familiar with Dallas black gumbo, but Houston grey gumbo is miserable stuff. You may have an expansive clay combined with a cracked slab. It will probably be hard to fix.

If it's not cracking the walls, I'd just shave 1/4 in off the bottom of the bathroom door.



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"Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

- Blair Houghton

 

[Clcrom]

Thanks ACtraffic,

I believe that you may be right on shaving off the door. I have been reluctant to do that, but it is much easier than the alternatives. One, not to serious, problem is that the stops on the door are only aboyt 3/8 inch. We had this room added to the house about 15 years ago, and the door stops they used were not like the stops used to be.

The door just started closing again a couple of days ago, so the problem won't resurface until next December. I will shave the door off then.

CLcrom

 

[tincan]

? Is the perimeter footing pier supported and the slab floating?

Tincan

 

[ashhafPE]

What type of piers are installed or tied to the foundation? Are they drilled shaft piers with a bell or are they footings,...etc?

How is the drainage around the problem area? Also are you watering around the foundation system or do you have a soaker hose around ?

Expansive clay soils will create an uplift. You mentioned you checked the foundation under the house! Is it a suspended slab
or a pier & beam with a concrete perimeter beam?

 

[JedClampett]

When we do work in Texas (normally near Dallas) the swelling clays are compensated for by several methods. When we use deep drilled foundations such as yours, we pour the slabs on "void forms." These are cardboard forms that are designed to intentionally rot away soon after the concrete is set. These means the subgrade clays do not contact the slab and this avoids large uplift forces that are very hard to support.
I suspect your foundation was sufficiently designed for downward loads but they neglected to pour the slabs on void forms. Hence your swelling problem during the rainy season.

 

[Clcrom]

Thanks for your questions and comments.

Th house is pier and beam construction. There is about a 24 inch crawl space. In 1992 we added couple of rooms and another 2 car garage to a 50 year old house. The addition was about 800 sq ft plus the new garage, which gives about 2800 sq ft of total living space. The new addition is essentially the same brick and frame construction as the old. The problem that I have talked about is in the new part of the house. However, some 20 years ago I had a similar problem with the old part of the house in another bathroom on the oppocite side of the house. I fixed that door problem by shaving the door off the top and side.

I made a video tape of the major activity when they were building on the addition. Your questions motivated me to dig out the video to provide more accurate answers than I could remember.

The piers are about 14 inches in diameter. The spacing of all piers including those in the foundation is about 6 ft. They drilled all the holes down to white rock first and then filled the holes with concrete to essentially the ground level. A heavy rebar was placed in the center of each pier base, which I believe extended nearly down to the rock. Next they doug the trench for the foundation. The trench was about 14 inches deep and the width of the foundation. They then installed the forms and the rebar for the foundation.

They tied into the foundation of the old part of the house by drilling holes about 4" into the old foundation to accomodate the rebar. The forms for the piers which were not in the foundation were made from some fabric like heavy tar paper. They just wrapped this fabric into cylinders and stuck nails thru them to hold them together. Of course, the foundation was poured over the submerged pier bases that were in the foundation line. After the forms were installed and all the rebar secured together, they poured all the concrete. Inspecters came between each stage of making the foundation.

The drainage is basically good, and we do water the foundation with a soaker hose during dry weather. We also have guttering around the entire house with down spouts that carry the water from heavy rain well away from the house.

One interesting thng about the problem is that it is seasonal and does not appear to be related to how much rain or how little rain we have in a particylar season. Soemtimes we have very wet springs and sometimes very dry springs. the same is true for the other seasons. But the problem starts becoming apparent in December and begins to disappear in late April or early May. I first thought the problem might be related to temperature, rather than miosture content inthe soil, but have decided that the ground temperture changes over the seasons shouldn't make that much difference.

I ceertainly appreciate your comments. Maybe its not too late for this old EE to learn something about CE.

CLcrom

 

[drobi]

Is there a tree close to the corner of the house that is moving?

In winter the moisture content of the ground would increase causing the ground to swell while in spring and summer the ground would dry out, any trees causing additional desiccation and the ground shrinking. This would be repeated year on year.

 

[Clcrom]

Yes, there is a pecan tree in our neighbor's yard about 20 feet from the foundation that seems to be moving up and down seasonally. Pecan tree roots roots generally run deep and a long way from the tree. The base rock is only about 6 feet deep, so I expect that the roots do run close to the foundation. Since the piers go down to solid rock, the force would have to lift the piers slightly off the rock. I doubt that the foundation is lifting off the piers because the piers are anchored to the foundation with the rebar. Since about May 30 this year, as in previous years, the foundation is down to the normal position, and the doors close just fine. I expect the condition to stay this way until sometime in December regardless of how wet or dry the fall and early winter season is.

Thanks for your comments. You may well have diagnosed the cause of my problem. It seems that the best solution to minizing the problem is to shave off the parts of the doors that stick.