Sine_Qua_Non
Sine_Qua_Non SuperDork
5/6/18 7:36 a.m.

Asking for a friend. She says

”Does anybody have any experience with this? Our house is on a hill and our foundation has sunk about 2 1/2 inches on the downhill side of our house. First company quoted us $70-90k for caissons. Second company says caissons aren't necessary and helical piers can be used. Quote is $20k. Obviously, we're going to get at least two more opinions/quotes.”

 

 

carguy123
carguy123 UltimaDork
5/6/18 8:05 a.m.
stuart in mn
stuart in mn UltimaDork
5/6/18 8:21 a.m.

Helical piers are really starting to catch on in recent years.  They still require some engineering to make sure the contractor installs the right size to the right depth, but they go in quick and as mentioned are pretty cheap compared to other options.

disclaimer:  my experience with them is for street light pole foundations - I have no experience using them for building foundations, but I have read a bunch about them.  The point is, they are a viable option and she should certainly consider using them.

Nick Comstock
Nick Comstock MegaDork
5/6/18 9:28 a.m.

It really depends on the weight of the structure and how it's constructed. I installed helical piers, steel resistance pilings, Mass concrete underpinnings and many other type of foundation underpinnings for almost twenty years. I'm short on time now but can add more later. 

Poured foundation walls or CMU?

Single story ranch with a basement or multiple story? 

Is the hill side sloughing off or is it strictly settlement? 

I can add more later.

Sine_Qua_Non
Sine_Qua_Non SuperDork
5/6/18 10:35 a.m.
Nick Comstock said:

It really depends on the weight of the structure and how it's constructed. I installed helical piers, steel resistance pilings, Mass concrete underpinnings and many other type of foundation underpinnings for almost twenty years. I'm short on time now but can add more later. 

Poured foundation walls or CMU?

Single story ranch with a basement or multiple story? 

Is the hill side sloughing off or is it strictly settlement? 

I can add more later.

“We have a 2-story, with concrete slab foundation. The hillside is not moving, we just have settlement. We have about 15 feet of level land between our house and where the hillside goes down. The house was built in 1969. We were told the reason the slab is sinking is because when they cut away the hillside to make the housing plots, they probably didn't do a great job with compaction of the soils.”

Nick Comstock
Nick Comstock MegaDork
5/6/18 10:13 p.m.

In reply to Sine_Qua_Non :

What part of the world is this house located? 

Antihero
Antihero HalfDork
5/6/18 11:02 p.m.
Sine_Qua_Non said:
Nick Comstock said:

It really depends on the weight of the structure and how it's constructed. I installed helical piers, steel resistance pilings, Mass concrete underpinnings and many other type of foundation underpinnings for almost twenty years. I'm short on time now but can add more later. 

Poured foundation walls or CMU?

Single story ranch with a basement or multiple story? 

Is the hill side sloughing off or is it strictly settlement? 

I can add more later.

“We have a 2-story, with concrete slab foundation. The hillside is not moving, we just have settlement. We have about 15 feet of level land between our house and where the hillside goes down. The house was built in 1969. We were told the reason the slab is sinking is because when they cut away the hillside to make the housing plots, they probably didn't do a great job with compaction of the soils.”

Slab on grade with no friction pile?

 

Ive never done helical piers but caissons is pretty proven technology. I am not an engineer either, but i have done concrete and construction for many years.

Sine_Qua_Non
Sine_Qua_Non SuperDork
5/7/18 12:09 a.m.
Nick Comstock said:

In reply to Sine_Qua_Non :

What part of the world is this house located? 

California

SVreX
SVreX MegaDork
5/7/18 1:00 a.m.

Hire an engineer. 

Thats the only right answer. 

Nick Comstock
Nick Comstock MegaDork
5/7/18 9:11 a.m.
SVreX said:

Hire an engineer. 

Thats the only right answer. 

That is the correct answer. An independent structural engineer is the way to go.

Based on what I'm hearing however it seems like helical would be a viable option. However beware that helicals typically are priced to a certain depth then if refusal is not meet at that depth there is a certain price per foot after that. In the areas I've worked it was fifteen feet then $28 per foot after that. I've had jobs double in price based on footage. I'm not familiar with Californian geology so I couldn't really even guess how deep one would have to go to reach refusal. An engineer would. Helicals have to meet refusal in order to work as designed. You can't just stop at a certain depth.

oldopelguy
oldopelguy UberDork
5/7/18 9:24 a.m.

If they use helical piers do they then also mudjack under the slab? I wonder how that whole process works.

Scott Hatfield
Scott Hatfield Dork
5/7/18 4:56 p.m.

If it hasn’t been done, please tell them to hire a competent geotechnical engineer familiar with the local geology and geo hazards.

 

Nick Comstock
Nick Comstock MegaDork
5/7/18 5:31 p.m.

In reply to Scott Hatfield :

You know, in all my years in that industry. And all of the engineers I've delt with. I can only think of one time a geotech was used and that was on an elementary school. I find that odd now looking back on it. But I certainly agree that it would be a smart move.

90BuickCentury
90BuickCentury Reader
11/25/21 8:49 a.m.
Christran said:

The problem with the sinking foundation seems pretty serious. Before making a decision, consult very well with a construction engineer.

Sinking foundation is pretty serious, but not as serious an issue as a sinking canoe, which will probably happen shortly... 

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