Lot prep / construction question

[Whitworth]

I'm curious.

When they're prepping large lots for sub-divisions, how long does it take for the earth to settle before doing foundation work, etc.?

In other words, is there a scientific/engineering method to measure compaction of the lot, or is it just drive heavy machinery over it day after day and hope for the best?

A development near my house, they blew out the trees and leveled off a steeply sloped area of several acres and are already building retaining walls. It's only been about 3 months.

 

[wssix99]

The earth will not settle on it's own. It needs to be compacted by natural or man-made forces.

When building foundations in an area that has been filled or has soils of unknown quality, geotechnical engineers can be hired to come out and test the soil after the foundations have been dug. They have various scientific tools available to them, like penetrometers, which allow them to confirm the compressive strength and other properties of the soil.

The house i am currently living in is on a lot that has been built on repeatedly for over 150 years. We had our foundations tested after digging and found that they were soft. We needed to dig deeper to find virgin soil that could stand up to the building. One area was super soft due to 100 year old cesspool and that area needed to be dug even deeper and have engineered fill put back in.

^ The money we spent on this testing was the best investment we made. (The house would be leaning otherwise.) Even though the deeper foundations and engineered soil cost a lot more, the consequences would have been catastrophically expensive.

 

[Walkers]

Start construction the same day. Compaction is something that you may or may no need. If needed simply test the current compaction and if not enough run a sheeps foot compaction wheel over the area needed and retest. Add AB for compaction if needed.

 

[Bondo]

Ayuh,..... They use one of these,......

 

[kbs2244]

I like to give it a year to settle
they leveled a local lot for an ACE store and let it sit for 2 years
This was in northern Illinois

 

[Spud McGee]

They will also compact as they fill. Spread 2" of dirt, go over it in north-south and east-west with a compactor. Bring in 2 more inches of dirt, compact it. Rinse and repeat.

You can see them doing that starting around 4:00 in this video on the sides of the new overpass. They build up what looks like 20-30ft of dirt, compacting as they go. A few days later, its got train tracks on it and the weight of a train on that dirt.

 

[ycgoat]

My understanding at least around here when I was doing construction so I may not be the expert, but for residential it needs to be virgin soil or it has to have a compaction test. Commercial slabs needed a test before they could pour

 

[Leaflessshadetree]

Most heavy equipment (especially tracked machines) don't compact as much as people think.

I had a friend ask me to haul in some dirt (with my pick-up truck) to fill a hole in his back yard. I went to look at what he needed and found a hole large enough to park the truck in (length, width and depth). When they built his neighborhood (10-15 years earlier) they filled in the gullies and this one was coming back. I showed him where his driveway and foundation were cracked as the whole thing was falling in.
He ended up with lawyers, engineers and all kinds of construction guys working for several weeks.

 

[firebirdparts]

I'm curious.

When they're prepping large lots for sub-divisions, how long does it take for the earth to settle before doing foundation work, etc.?

In other words, is there a scientific/engineering method to measure compaction of the lot, or is it just drive heavy machinery over it day after day and hope for the best?

A development near my house, they blew out the trees and leveled off a steeply sloped area of several acres and are already building retaining walls. It's only been about 3 months.

Traditionally, they used sheep feet to compact soil in big areas. That was the old way. The sheep had a lot of spare time, so it worked out. Eventually somebody built a roller that looked like sheep feet and that was much easier to deal with. For foundations, of course, you can just compact a small area and people use smaller machines for that. They might have rammed the area they're working in without you noticing.

I wonder what sort of retaining wall that is and their attitude about a foundation under it. Retaining wall "philosophy" is pretty diverse compared to building houses.

 

[Spud McGee]

Most heavy equipment (especially tracked machines) don't compact as much as people think.

I had a friend ask me to haul in some dirt (with my pick-up truck) to fill a hole in his back yard. I went to look at what he needed and found a hole large enough to park the truck in (length, width and depth). When they built his neighborhood (10-15 years earlier) they filled in the gullies and this one was coming back. I showed him where his driveway and foundation were cracked as the whole thing was falling in.
He ended up with lawyers, engineers and all kinds of construction guys working for several weeks.

Yep. The tracks on equipment are designed to spread out load. Overall PSI under the tracks is relatively low.

 

[driftpin]

I've seen these ways.

Compaction done in 'lifts,' where a certain amount of soil of known quantities (% of sand, humus, etc) is placed into an excavation, and then compacted. More soil, more compaction, until the excavation reaches whatever height was needed by the soil testing and P.E. calculations said. Like Spud McGee said.

Another way was to place an immense amount of soil onto an area to be developed, where it forms a hill. This is left for a pre-determined amount of time, and then the soil 'hill' is moved along, to compact another adjacent area. And so-on.