OT: House Foundation Peirs

Obviously way off topic, but there's a lot of smart guys on this forum and some of you probably have some experience with this. Hopefully this doesn't get deleted.

I live in an area with unstable soil. Irving, TX. I think it's clay. Foundation problems are really common around here.

My house has a slab foundation and a porch on one side that is sagging a little. I looked into getting piers installed. They use either concrete blocks or steel pipe and press them into the ground until they hit something solid. That could be rock or harder dirt.

My question is, does it really help? Unless you hit rock, which I'm not sure will happen at my house, it seems like the weight of the house will slowly, or not so slowly, push them further down until they're no longer helping to support the foundation. You're right back where you started with the same foundation sag.

Pipe piers are suppose to be best but they have a very small footprint. Unlees you hit rock they don't seem like they'd help at all.

Any thoughts?

Here's the porch.

There are many foundations made on what are called Friction Piles. Common for large buildings where there is no bearing material underneath the foundation. Here's a high level description: Friction piles - Designing Buildings Wiki More details:What is Friction Pile? Capacity Calculation & Details - Civil Engineering

I'd also look into screw pilings. They might be usable for your problem. I had a friend that had a foundation done this way and is very happy after 8 years or so. Here's one company: Helical Piles - Screw Pile Foundations - Techno Metal Post

Here's an article about a problem like yours: https://www.jlconline.com/how-to/retrofitting-a-foundation-for-problem-soils_o

Not sure what the best way to fix an existing foundation would be. My Tx shop is built on black clay, and slab is cracking, if I was to build again I would drill 3' diameter holes in multiple locations down to the gravely tan clay layer 6 to 10 feet below surface, I think its a bit more stable. Biggest problem with black clay is it expands when wet and shrinks when dry, some people believe keeping the clay wet helps, idk. Have you drilled any holes to see what is below grade?

Look at the piles holding up a pier. Just pile driver into the mud/sand until it is deep enough to hold the weight. The Taj Mahal and much of Venice Italy is built on multiple piers with stone buildings on top.
To underpin a foundation to make a basement deeper they dig out 3 foot wide piece at a time under the perimeter foundation so piers every three feet or so seems about right. Probably closer with a slab foundation since it does not have a grade beam.
Bill D.

Not that it will help in your situation. There is also a Raft slab which is basicly a thick concrete slab, 12-18" thick IIRC, on the house I did some work on. This has NO footings, just a concrete "raft " to "float" on top of wet soil.

The type of solution that will work will be dependent on the soil types and conditions in your area, for example, we have clay in Vermont but foundation design is a lot about the depth of frost. I would trust a company local to you that has been doing the same thing in the same area for a long time, also a company that has a civil engineer on staff. Sometimes slabs can be jacked up by pumping a slurry under them. I would not be surprised if the least expensive option is to remove existing slab and put in a proper footing, compacted gravel and new slab.

Gard said:

but foundation design is a lot about the depth of frost.

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Its Texas, frost depth is 1/4" max.

What you want to do is spread the load and transfer the load down to soil which has a steady water content. Your porch is probably slowly squeezing the pore water out of the soil. Think Millenium Tower in San Francisco. You have not said whether the porch goes up and down seasonally with soil water content. I know that expansive clay soils are a big issue in the Houston area; don't know about Dallas. They are somewhat of an issue here in the SF Bay Area. The amount of shrinkage and expansion with changes in soil moisture can be shocking. The issue can be addressed by transferring the load deeper to clay soil that has steady water content year-round, and, equally importantly, decoupling the foundation from near-surface soil that continues to shrink and expand seasonally. On way is to interpose a deep bed of crushed stone under the slab during original construction. No solution is cheap after the fact!

Friction piles have been in use for many, many years and they work. When I was in second grade I attended a parochial school. They were building a new church building next to the classroom and I had a grandstand seat to the process of building the foundation. I was totally amazed when the pile driver started a new pile. It was a hollow steel one which would later be filled with reinforced concrete. When the steam driver head was dropped on the pile, it immediately sank about 1/2 to 2/3s of it's length. After that it only took a very few power strokes to sink it all the way. Like dropping a rock into water.

The second steel section was welded onto that first one and again it went in easy. It only started to slow down near the half way point of that second section. Then a third one was welded on and, finally, things got slower. At the end of that third section it was going only a few inches for each power stroke. That is just how soft the soil is in the New Orleans area. Whole buildings have sank significant amounts and others have tilted. That church building still stands, with no noticeable sinking. Friction piles do work. And they work for close to 60 years now in that case. I know, I have revisited that church.

Soil conditions will differ. Companies, contractors in your area are the ones to talk to. They should be well informed. Do talk to more than one.

I'm familiar with the clay he is talking about - I come from that part of the world & went to architecture school within 30 miles of that location. It is expansive. It shrinks when dry, then swells back up with water. Issue is that the soil at the perimeter of the slab changes moisture content with weather, but the soil under the center of the slab doesn't.
One of the engineering profs suggested pouring a low-quality concrete "wall" say a couple feet deep around, but not attached to, the slab to stop the moisture movement. Not sure mama would like that look, but it would work to stop such damage.

Pressed piers are your best bet. They have been a standard repair for years now and I have had several houses repaired that way. Our clay soil is pretty bad for building on as it shrinks and expands depending on the weather, and there is nothing you can do about the weather.

When building on this type of soil I always have Gessner Engineering, out of College Station, do core samples and design the foundation. Almost always they have me remove at least 4 foot of the soil replace it with compacted select fill and then drill piers! . NOT every "select fill" is good and I always have them test that soil for use. Once I had 3 pits sampled before I found one that passed and I would give you a 100.00 if you could tell me, by looking at them, which was which. Point is always test..

Now for your problem... I personally have a machine for pressing in the piers and have done a few houses myself. It cost nearly 4000.00 and is made especially for this job. The cylinders are cheap, easily sourced and there is not really much to installing them once the hole is dug They are forced into the ground to the "point of refusal" where they just will not go father and the structure lifts.

The depth of point of refusal varies greatly even on the same house. I had one house where it was all I could do to get them in 8 foot, even piled bags of gravel inside the house where I was pressing for more weight. 20 feet away they went in 18 feet! You just never know...

In the 70's everyone was building spec houses in Houston and bragging that their houses had 8 foot deep piers. 6 or 7 years later everyone was cutting the piers off because they were not deep enough and dragging the structure down into the mud. You must go deep enough to contact a stable clay that is not subject to movement! The poured piers under my house are 22 feet deep.

Think about a boat on a lake with an 8 foot long anchor rope.. As long as the water depth is under 8 foot your ok... Over 8 foot and all you have is an anchor hanging straight down, pulling your boat down... And as my Wife would say "Gravity is a Bitch"

The pressed in piers are a good way to repair the home. You Must find a reputable company to do the work. I have used olshanfoundation.com for the last 20 years on big jobs. You want a good warranty and someone who is still in business to back that warranty up....

IF you want to do the job yourself...... I could always sell your my machine....

I would think a chemical grout might be the least costly option......Obviously ,pulling the porch down and rebuilding isnt an option ....however any cheap piling option will need direct overhead access....usually reactive soils also allow an outward movement as well as down and pier foundations splay out as well as settle........One old house on black soil I demolished had a large size anchor chain all around the stone block foundations .....Black soil is notorious for radical movements,yet the old house was 150 years old ,and the stonework hadnt cracked anywhere..

We call that type of construction " floating slab". Same thing ,different name. Of course this would only work on new construction. Expensive, but often the only way to build on unstable ground.
The OP should consult an architect or engineer, though I have many years of experience in concrete construction, does not qualify me to give advice.
mike

I live in Keller TX, not too far from the OP. Ours is a 1500 sq ft slab foundation, located on a steep, rocky slope. Neighbors said the builder had put down massive piers before the slab was poured. We bought it in 2001, 3rd owner.

I used a local contractor with a good reputation to level our house about 9 years ago. He told me one corner was low about 3/4". We let him basically do the whole perimeter just to make sure everything was stable/.

After they left, we found cracks and mishapen door frames all over the house.
Now, one of the walls that prompted the inspection in the first place has subsided more and is cracking the mortar.

In my opinion, this was $5000 wasted.

I have heard The Taj Mahal will collapse in 50 years. It sits on wooden pilings driven into wet soil with brick building on top, sheathed in marble. farming is drying out the soil and allowing air into the wood piles. this water air interface will allow the wood to rot and collapse everything above after about 400 years.
What is the modern foundation like for the leaning tower of Pisa?
Bil lD

Many years ago I worked for the City of Carrollton and, yes, this is a big problem throughout much of Texas. I remember the City Manager at a public meeting said he was so tired of dealing with road complaints from shifting soils that he wouldn't take his next job anywhere that had similar soils.

Most of the comments from your fellow Texans are spot on about the problem and how to deal with it. I'll add in that when I had to do some foundation repairs to walls in the basement I picked RamJack not because I thought they would do the best job, but because they offered a lifetime guarantee, transferable to the next owner, for the work done. That guarantee paperwork was prominently taped to the basement wall when I put the house up for sale. Ask about that from the contractors.

Steve

A Little Off Topic

I recall my dad telling us one time, back in the 1960's, the company he worked for was located down in south Houston, off of Homes Road, many of you guys know where I;m talking about. They had a long bed machine, thet the foundation under one end kept sinking in the ground. The foundation was over 3 foot thich, too. They bored holes thru the foundation, set pipes, and had Halliburton bring in a pump truck. They pumped cement slurry for two days with no indication of it working before giving up. That's how gumbo that swampy ground is in the Houston area is. I feel sorry for the company that decides to bust up that concrete foundation. They maybe busting concrete for months on end, who knows! Ken

Bill D said:

What is the modern foundation like for the leaning tower of Pisa?
Bil lD

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This will give some background: Leaning Tower of Pisa Corrects Itself... a Little - Scientific American

Neat tidbit - LToP isn't ever going to be straight up and down, no matter the correction efforts, as it itself is curved.

Rex TX said:

In my opinion, this was $5000 wasted.

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That sounds like an unfortunate truth. No help from the contractor?

While I've never lived in TX, I've had some awareness of the mushy soils for a while, as there's a racetrack that was built near Austin that's had a lot of problems with soil movement.

Circuit Of The America’s Bumps And The Famous Shrink-Swell Soils Of Texas | Cycle World