Replies

1. 
   Bruce_M | Feb 22, 1999 08:08am | #1

   *
   Hi Steve
   what you are experiencing is the effect of hydrostatic pressure bearing in on your basement walls. This happens because water accumulation near your foundations purcolates easily down through the foundation fill that was losely pushed in place, but then the water slows its migration considerably when it contacts the normal hard-packed and undisturbed soil surrounding the lose fill....and is particularly bad if the surrounding undisturbed soil is heavy clay. When the lose fill is fully saturated (which is what usually happens when it rains hard over several days or you experience large snow melts), it exerts considerable force against your foundation wall. Imagine that you have a moat around your house' foundation walls that is 7 or 8 feet deep and 3 to 5 feet wide at the top, narrowing to 1 to 2 feet at the footing....indeed, it would push your basement wall in.
   It sounds like drain tile were either never installed around the outside footings or they were and are now silted in with earth or the drainage is blocked.
   You are correct in rerouting water away from your foundation wall, as this is the source of the excess moisture that ends up pushing against your foundation walls. You should also make sure the grade from your house slopes away from the foundation walls, as this will help divert some of the moisture from purcolating down.
   As to your buldging wall...I don't know of anything you can really do, except to reduce the external hydrostatic pressure and hope there is enough back 'spring' in the wall to bring it back to its original position. This summer when (hopefully) the rain/snow stops and the ground dries out and shrinks, you will know.
   Best

   Bruce M

2. 
   Guest_ | Feb 22, 1999 08:10am | #2

   *
   I don't know your experience level with this type of situation but the first step is to prevent further damage and you have started by diverting the water.

   You should tell me what part of the country you're in so we can have a better idea of the possibilities, such as if it was frost damage or what.

   Sight unseen I would have to quess that you would have to excavate first to do a proper and complete repair to the masonry, the damp or waterproofing membrane and drainage systems to your house.

   This isn't a matter of putting back a few blocks and alls well in the yellow brick house.

3. 
   Steve_A. | Feb 22, 1999 08:42am | #3

   *
   Thanks Bruce and Gabe. I live in southern Illinois and the soil is heavy clay. This problem has developed gradually over several months. At this point, we do not know if there is a drainage system, but assume there is and it is probably silted up. We are considering possible options and a big concern in the worst case scenario is how to support the brick veneer wall while removing the block wall. According to the FH article, they suggest replacement only if the wall has bowed over an inch. Therefore, at this time, we are considering coring the wall and tying to a concrete beam on the outside of the basement. We are also considering building pipe jacks from basement ceiling and floor to stop movement and possibly return the wall to original position.

1. 
   figuers | Feb 23, 1999 08:43am | #4

   *be very careful what you do. Bruce is only partially correct. Hydrostatic overloading is a common cause of wall failure, but it is not the only cause (for a 10 high wall, free groundwater will increase the loads on the wall by 25 to 30 percent). A basement wall is a restrained wall. That means that the top of the wall should not move at all. If it does, it will shift what ever is sitting on top of it. The typical retaining wall that you see is an unrestrained wall, it is designed to tilt slightly to allow the soil to carry some of the load. This is where the 1 inch deformation rule of thumb comes from. Your description of the distress is consistant with an unrestrained wall acting as a restrained wall. The normal soil loads on the wall caused it to tilt, but the house framing prevented the top of the wall from shifting. Therefore, the upper part of the wall cracked and bowed outwards. The deformation is permant. It will not 'spring back'.The problem with unrestrained walls and clays is that initially, the wall tilts and the soils carry some of the load (as it is supposed to). Over time (years), the clayey soil creeps towards the wall, increasing the soil loads on the wall. The wall then tilts in response to the higher loads (as it is supposed to), and the entire process begins again. over 30 to 50 years, this process can cause a wall to tilt 1 to 2 feet.Before you do repairs, you need to determine if the wall tilting was caused by hydrostatic loading or an underdesigned wall. If it is hydrostatic loading, it would have occurred quickly in response to a very heavy rain fall. Is the basement wet, are there indications of water flowing through the wall, was there a very wet winter, is there a roof downspout just above the damages section of the wall, has the tilting been going on for several years? These are some of the things you should look for. Is there reinforcing steel within the wall. If not, then exterior reinforcement will be of little help (there is nothing for them to support). The best thing to do is rebuild the wall as a restrained wall.

1. 
   Fred_Matthews | Feb 23, 1999 10:07am | #5

   *SteveYours is a complex problem. You say you live in an area w/ "heavy" clay-is it expansive clay? Diverting the surface drainage will help once the problem is corrected, but you need to take the corrective action first. Possible solutions could include strongbacks and/or reinforced pilasters (on interior). The first solution stiffens your wall to act as a horizontal beam, the latter stiffens the wall w/ vertical buttresses and reduces the horizontal span of the wall. Contact some experienced foundation contractors or engineers in your area.

4. 
   Guest_ | Feb 23, 1999 08:53pm | #6

   *
   To those that know,

   Aren't homes with foudations built in clay areas supposed to be backfilled with sand and just topped with the clay to seal out rain? That takes care of water and also eliminates expanding clay next to the foundation pushing it in. Sortof like "three birds with one stone."

   I'm for digging out the problem clay and installing sand to fix it properly verses building nuclear containment walls.

   Skip the layered solutions, keep it simple,

   Jack : )

5. 
   figuers | Feb 24, 1999 06:44am | #7

   *
   Adirondack Jack

   Supposed to and reality are generally two different things when it comes to construction. If you back fill with sand (to prevent clay creep), the sand fill should be trapizodal in shape. One foot or so wide at the base and several feet (4 to 5 feet for a 10 foot high wall) at the top. Virtually no one does this in clayey soils because of the cost. They use gravel and design it as a sub-drain. if you do not provide an outlet for the subdrain (either a pipe or daylight it if you are on a slope), you have created a bathtub - and will cause the damage you were trying to prevent in the first place.

   The clay cap is useless in keeping water out. The first thing home owners do is dig up the ground and plant bushes. You now have a compacted clay cap with a series of 1 foot diameter holes in it (otherwise known as a sieve, or to use the lingo - a series of prefential flow paths). It also has no effect on keeping out ground water (lateral flow of water). This can be a significant source of water on slopes (up to 80 percent of flow).

   Jack's solution does not address the problem of an underdesigned wall. no matter what you do around the wall, if the wall cannot support the loads, no amount of improving the soil or drainage will fix the fundamental problem

6. 
   Guest_ | Feb 24, 1999 07:44am | #8

   *
   figuers,

   My way is the "book" way and it works where I'm from. We have all kinds of sand in pits everwhere and its very inexpensive. Winters Frost push in clay soils is a big problem that the sand solves because the sand doesn't push like clay. The water "tub" if there like you describe would be a nightmare no matter what you do. I don't build in underground rivers or below water tables.

   Lastly, I never spec block in soils other than gravel which we do have a ton of in the upper Hudson Valley. For clay and or stronger foundations, poured walls are my choice, and can be built quite "nuclear" depending on the amount of steel in them...

   Not an expert, and usually steering clear of clay,

   Jack : )

7. 
   Steve_A. | Feb 24, 1999 07:48am | #9

   *
   We have a 30 year old brick veneer house sitting on a 12 inch concrete block basement wall. Between the fourth and fifth block from the top, the mortar joint has opened up and the wall has bowed in 11/16ths inch at the maximum point which is at the center of the thirty foot side wall of the basement. We have temporarily installed gutter drains to divert the surface water. We have read the recent Fine Homebuilding article on repairing basement block walls and would appreciate any additional advice and/or experience that anyone might have. Thanks. Steve A.