Water injection on uncontrolled fill 1

[JeremyLee17]

This residential site has expansive clay. It appears that the building pad is poorly compacted, dry, in-situ clay scrapped from the surface of the surrounding area. The building pad levels a slope with a max depth of 5 feet.

I provided the geotechnical report and I am to design the foundation. I specify in the report, by email, and on the phone the risk involved with building a slab-on-grade under these conditions.

The contractor communicated by phone call that he will use water injection on the building pad.

It seems to me this contractor has only one plan in mind: To push dirt in a pile and build a slab-on-grade. I don't think he intends to use water injection and he will not specify his intentions over email. I feel there is a good chance I will not get compensated for any performed work.

My questions are:
1. If the pad is water injected AND I take samples for a swell/settlement under expected loading AND neither swell or settlement is significant, could there still be significant long term 'secondary settlement'?

2. If I design the foundation I don't think it is my uncompensated job to catch them building it improperly, but at the same time I don't want to design something when there is this much obvious risk. If I make it clear the risk involved with the contractor's plan and go forth to design the foundation, would I be acquiring unreasonable liability?

 

[Eric C.]

So, there is a pad constructed of poorly compacted, expansive clay varying in depth up to 5 feet upon which you are asked to design a foundation that you likely won't get paid for?

My opinion is that you may cut your losses if you send a report stating your concerns and offering recommendations for him to improve the site and you would be happy to design a foundation once the corrections are made and verified. (You may could copy the AHJ) Send him and invoice, too. If you get paid it'll be like you won on a scratch off lottery ticket.

 

[oldestguy]

My take is steer clear of this. Looks like nothing but trouble. A nice letter stating you are very busy and suggest another engineer in the area.

 

[Mad Mike]

I would just be firm on the design you're willing to undertake- bypass that dirt pile using deeper pads, improve the platform layer for the floor slabs- write off the slab on grade as a risk you're unwilling to take, given the perceived incompetence of the contractor and the current building pad not complying with the local standards. There may be more to this than just the settlement/swell under load...a shoddy dirt pile will deteriorate in the years to follow.

If they want slab on grade, have them remove and reconstruct the building pad to an acceptable standard. Ask for your payment in advance.

Best,
Mike

 

[Ron]

Water injection on a dry, expansive clay is a recipe for disaster. It will dry again and the resulting settlement will not be pretty. Same but opposite condition if you compact the dry material without appropriate mitigation of the expansion.

Run away now.

 

[MTNClimber]

Water injection does work if the site will be irrigated after construction has been completed. If left alone to dry out for years then you’ll have problems.

That said, I agree with everyone else. Avoid the headache - run. This project has disaster written all over it.