Concrete and Automotive Lift

[Lowlyslows]

Hello!

New to the site, not sure if I am posting in the right location or not.

I am trying to figure out what to do with an automotive lift install for my garage.

My slab is 4" thick, 3500psi, with structural grade beams and wire mesh. The instructions for the lift calls for at least 4.25" slab thickness, 3000psi, and steel bar reinforced concrete. So, I don't meet the minimum requirements. The lift can support up to 6,000lbs.

I spoke to an engineer yesterday. He doesn't like the idea of me just putting the lift on what I have. My house is a walkout and the garage is attached on the side. When they built the foundation (2018), they dug down to pour the footers which are about 8-9 feet below the concrete slab in the garage. Then they backfilled the garage and didn't compact the soil. The slab is supported by 4 concrete beams going across the garage (horizontally and perpendicular to the garage door entrance). So, if I open up the concrete to get a thicker slab, I have to do it between the beams, engineer doesn't want me touching the beams. That's not a big deal through careful measuring. My issue is the soil, solid earth starts around 8-9 feet down so I got to figure out how to get to it to support the lift. This is coming from the engineer.

I'd like to get some opinions from anyone willing to give them on what to do here. Lots of other guys just cut out a section of concrete and dig down a bit a pour new concrete. None talk about the support required by the soil.

I attached a power point of what I am working with, pictures, and some ideas the engineer and I talked about. Any help is greatly appriciated.

-Paul

 

[BigH]

Interesting problem. What concerns me is the fact that the contractor did not compact the soil below the garage slab. And you have made no mention of the type of soil that was used in the fill. Sand? Clayey (cohesive) soil?

8 to 9 ft excavation will require shoring if you want to open it up (3 ft by 3 ft as you said) and "enter" the excavation to clean the bottom when hitting firm soil. If the material is sand, this is a no-no as the sand will run and you may undercut the beams that are supporting the garage floor slab. If clayey, as it wasn't compacted you might be able to see it stand but OSHA would be aghast so that is a no-no. You want to keep the cut in the slab as small as possible.

How high is the garage ceiling? i.e., clearance. What I would like to suggest is to use micropiles using low headroom equipment. You could likely get away with 4 small micropiles taken a few feet into the competent soil (presuming it is) at each of the corners of the garage cut-out's two locations. A pile cap connecting them and to be flush with the garage floor. The picture of the lift shows one with extending "feet" and the other not having them. I like the former as you would want to keep away from any potential bending moments.

Another possibility is to hand-drive 35 mm rebars down into the competent soil - again at least a couple of feet into it - likely drive 9 bars per location. You could hand auger down a few feet to start the hole. Again - just some suggestions. The bottom line is that if you want to reach the competent ground I do not think you would want to excavate down to it.

You indicated you had spoken to an engineer (presumably structural as he doesn't want you to touch the beams). What does he think? He should be in a position, knowing the local conditions, etc. as to the best way to support.

Just some quick thoughts - you will get many more other alternatives.

 

[Lowlyslows]

BigH,

I completely forgot the soil type! I’m in northern VA, we have clay. Garage ceiling is 10.5 feet.

The micropile looks doable but I don’t think I have the ceiling space for the equipment. I have been looking into a well digging tool to hand dig down into the solid soil and then add rebar.

https://www.amazon.com/gp/aw/d/B00002N8OE/ref=psdcmw_3753981_t1_B01BM3YCHU

Just an idea for now.

Thanks!

 

[BigH]

As it is clay - you might be able to use motorized hand auger.

 

[HouseBoy]

This seems like a perfectly good application for Helical piers.
Cut out slab in the two lift post locations and have them installed and then use a flush concrete pile cap.
Around here (Cincinnati OH) I think one company that I have spoken to does the installation for about $500 each (but I think they have a 4 pier minimum).
You'll have to see about that and then there's the demo and replacement concrete but that should give you a good idea of what to expect.

Micro-piles (what are sometimes called "push piers") do not seem like a good choice as you do not have much weight to push against.

 

[Rogue909]

Consider beefing up the base of the lift to distribute load over a wider range of concrete.

We installed a 4 post lift in our garage. I can't remember the specifics (this was a few years ago) but the concrete call out was 1-2" thicker than our slab. Cutting concrete wasn't (isn't) my forte so instead I found a couple of 24" round steel x 1" thick on craigslist. Beveled the edges to avoid toe points, added an excess of anchors around the outside, then mounted the lift to the plate.

It's a bit of a 'do what you can with what you got' fix instead of a 'manufactured approved' fix but with the 4 post lift I felt confident it was unlikely the equipment would tip. I'm not sure I would be as confident with a 2 post lift.

 

[PEinc]

Names and locations of helical pier installers in Virginia:

https://www.google.com/search?rlz=1...wAhVyGFkFHZATCbYQtgN6BAgJEAQ#rlfi=hd:;si:;mv:

[[39.535023699999996,-75.8291306],[36.668557899999996,-80.2430967]];tbs:lrf:!1m4!1u3!2m2!3m1!1e1!1m4!1u2!2m2!2m1!1e1!2m1!1e2!2m1!1e3!3sIAE,lf:1,lf_ui:2

http://www.PeirceEngineering.com

 

[Lowlyslows]

Thanks for all the responses. Didn't know about helical piles, what a great idea. I have a guy up in PA from technometalposts.com that is going to help me out. Very much so looking forward to getting this done.

 

[jayrod12]

I'd be a bit weary of helical piles for a 2 post lift. They don't have a whole lot of lateral or moment capacity in the shaft. A 2 post lift will require that there is some form of fixity provided by the base structure. I don't see that in a helical pile generally without going to a significantly sized shaft.

I've worked with a Techno Metal Post supplier locally here and they have been generally quite accommodating to work with.

 

[PEinc]

It would be a good idea to have a minimum of 2 helical piers, about 3' apart, under each of the two lift legs to give some rigidity in the longitudinal (in line with the car) direction. I assume that the top beam between the legs has rigid connections at the top of the legs.

http://www.PeirceEngineering.com

 

[Lowlyslows]

Jayrod12 and PEinc. The lift doesn't have a top beam. Techno Metal Post has an engineer that is working to provide a solution on what pile to use for the possible weight. Not sure if he/she is going to consider the lateral aspects of things.

Question: What about keying the new concrete under the existing slab as well as dowels into the existing slab to provide support? Anything that can be done with concrete to provide the support?

See attached.

 

[PEinc]

The 9000# lift capacity should not b a problem for 2 or more helical piers. I would be more concerned about lateral stability of the lift posts. The helical piers do not provide much lateral resistance. Your new concrete at the top of the helicals, at or just below the floor slab, will need to provide the lateral resistance. You need someone to determine the required lateral resistance and then check that your new concrete can provide the resistance. Can your helical pier designer do that analysis?


www.PeirceEngineering.com