Cut and fill for house pad

Hi all
I'm from Perth WA eastern hill region and am about to undertake some earthworks. We are on a sloped 6 acre block and I'm going out of my mind with researching how to cut and fill. I swear I've read every paper there is but lack the practical ground experience having never done the job or watched soils enough to know how they settle. But I'm very capable. So to all you experienced folk out there I have a couple of questions. What I intend to do is:
- our block is a 12° slope
- the soil type is mildly reactive
- due to room restrictions and costs of fill best bang for buck solution is to have the majority of the house on the cut side and a small amount on the fill side.
- the cut side will slope 1.5:1 and the fill side 2:1
- compaction will be with a twin roller 2.5 tonne with lifts of no more than 200 mm of river sand virgin quarry sand, total 800 mm
- the embankment will be 2.5 meters at its highest point and will be benched and compacted again 200 mm lifts
- embankment will geowebbed and grassed
Q 1. can I use the cut soil for embankment and
Q 2. how important is Optimum moisture content, and how do I calculate it without getting a geotech in.
Am I getting carried away with the science?

We work on slopes a lot. One house we did in Big Sky, Mt had 25' of drop in the footprint of the house. Most are not near that severe, but you get the idea. Typically the house would set on the cut side as you stated, excavate down to footing depth, then as the house crosses the point where you run out of cut, drop the footings down to a depth that your footings stay on virgin ground. We avoid when possible putting the footings on compacted material. However when we do, we use structural fill (pit run is what we call it) and pay to have the compaction tested. Typically it is easier and less costly to do step footings and just stay on virgin soil. As far as compacting sandy soil, it takes a lot of water in my experience to get 95%. If you need to test your compaction, you will need a proctor on that soil to get a real compaction test that means something.

You had better get a geotech company in there to evaluate and design what you need. Better to spend the money now, than spend a lot more later for a foundation failure. ASTM has all the standards and procedures for a soil proctor and soil compaction testing. Let a professional look at it.
Jeff

In all my cases of dealing with engineers and foundations, they always want them on undisturbed ground, compacting has never been an option, the only fill option is washed rock. I've done a few walkouts in tree areas where if it's within 6" I excavate out all the crap and the footings just vary a bit if the customer wants to achieve the most height, because increasing height of foundation wall can get pricy with extra engineering. The other thing is, the basement floor isn't nearly the same concern, a bit of fill and packing is fine. If it's on a big slope chances are the house is a walkout? Here it's stepped footing for those where the walkout is, so they are 5' lower and not an issue anyway. But you definitely need a geotech to check out the soil, here they only charge like $250 to come out and access after excavation to make sure everything is good.

Around here we would fill and compact in 8 inch to 1 foot lifts with a wheel loader with whatever came out of the cut unless its highly expansive soil but most times its cut and compact if there is oversize rock in said material we grizzle it out in the process

Some geo will spec an over excavation of the cut side to be filled back to sub grade they do this for differential settlement witch I think is assinine our house footings dont have to be in native if you have a soil's report and certified pad witch requires a geo and compaction tests

In sandy soil water is your friend and optimum moisture is a judgment in the field more than an exact just knowing how wet is to wet is the key

KSSS said:

We work on slopes a lot. One house we did in Big Sky, Mt had 25' of drop in the footprint of the house. Most are not near that severe, but you get the idea. Typically the house would set on the cut side as you stated, excavate down to footing depth, then as the house crosses the point where you run out of cut, drop the footings down to a depth that your footings stay on virgin ground. We avoid when possible putting the footings on compacted material. However when we do, we use structural fill (pit run is what we call it) and pay to have the compaction tested. Typically it is easier and less costly to do step footings and just stay on virgin soil. As far as compacting sandy soil, it takes a lot of water in my experience to get 95%. If you need to test your compaction, you will need a proctor on that soil to get a real compaction test that means something.

Click to expand...

That is one option that I will discuss with the engineer. IE the dropped footing to the fill side. I think that's smart. Is out run a granular sand? or small rock ??

AzIron said:

Around here we would fill and compact in 8 inch to 1 foot lifts with a wheel loader with whatever came out of the cut unless its highly expansive soil but most times its cut and compact if there is oversize rock in said material we grizzle it out in the process

Some geo will spec an over excavation of the cut side to be filled back to sub grade they do this for differential settlement witch I think is assinine our house footings dont have to be in native if you have a soil's report and certified pad witch requires a geo and compaction tests

In sandy soil water is your friend and optimum moisture is a judgment in the field more than an exact just knowing how wet is to wet is the key

Click to expand...

hey thankyou for that logical advice I tend to agree with you on the practical aspect rather than all engineering equations. my structural engineer had said to use the cut soil as fill as they're testing says it's fine though not to be used on the cut side as a pad for the slab. ta

divo247 said:

That is one option that I will discuss with the engineer. IE the dropped footing to the fill side. I think that's smart. Is out run a granular sand? or small rock ??

Click to expand...

It is typically a 6" minus with a sandy texture. It is everywhere here, and compacts tight.

Nothing at all prevents you from backfilling that lower portion of the footing and doing whatever you want fill wise after the fact. It's a great option to excavate to native and buy a little more stem wall. one advantage to having a tall section in your crawl space is access and also Root cellar storage. I know that when we build our last house it will have an unfinished basement, just so any work I want to do down there is easy. The next owners can finish it and reap the benefits.
EDIT: my apologies I did not see the slab on grade.

The best tip I can give you is to use a pad foot roller for earthworks. Using a smooth drum roller causes the fill to laminate allowing moisture into the filled area. Thoroughly compact each layer to the point that a vibrating roller will start to bounce. Moisture levels in the fill material should be around 10% give or take depending on material type. An easy way to check is to grab a handful of dirt and squeeze it. It should hold its shape, then press your thumb onto it. If it crumbles to dust= to dry, maintains it's shape=to wet, crumbles into lumps is good.

You're over thinking it a bit.
Generally you dig to stable earth to place your footings. If you need to fill, use a self compacting fill. Usually rock chips with no fines.
And double and triple check your house elevation. Make sure rain water flows away from the house.
Take pics of the place and post them. I'm sure us armchair quarterbacks can give you some good advice!

skyking1 said:

Nothing at all prevents you from backfilling that lower portion of the footing and doing whatever you want fill wise after the fact. It's a great option to excavate to native and buy a little more stem wall. one advantage to having a tall section in your crawl space is access and also Root cellar storage. I know that when we build our last house it will have an unfinished basement, just so any work I want to do down there is easy. The next owners can finish it and reap the benefits.
EDIT: my apologies I did not see the slab on grade.

Click to expand...

You guys in the states build more cellars than we do here in Australia. It actually would have been a great idea on our sloping block but it's cost prohibitive for us. thanks

Tones said:

The best tip I can give you is to use a pad foot roller for earthworks. Using a smooth drum roller causes the fill to laminate allowing moisture into the filled area. Thoroughly compact each layer to the point that a vibrating roller will start to bounce. Moisture levels in the fill material should be around 10% give or take depending on material type. An easy way to check is to grab a handful of dirt and squeeze it. It should hold its shape, then press your thumb onto it. If it crumbles to dust= to dry, maintains it's shape=to wet, crumbles into lumps is good.

Click to expand...

I appreciate the advice. I've had the thought about the sheep foot roller and your experience makes perfect sense. It sounds like you have tried both drum and sheep foot and that is the exact advice I'm looking for to make a judgement on what I get in the end. Thankyou
Just an add on I feel the sheep foot roller would be the way to go for my fill side embankment as the soil has stone in it and a slight amount of clay.

skata said:

You're over thinking it a bit.
Generally you dig to stable earth to place your footings. If you need to fill, use a self compacting fill. Usually rock chips with no fines.
And double and triple check your house elevation. Make sure rain water flows away from the house.
Take pics of the place and post them. I'm sure us armchair quarterbacks can give you some good advice!

Click to expand...

Yes that is my problem. I'm a perfectionist at heart. However it's difficult when you have limited real world experience. As I don't have the time and money for trial and error. It's a bloody double edged sword. It's also our dream home so I'm trying to make it allot can be. I think once I get cutting and compacting and testing it will make more sense in the field. Thanks again

You guys have all been great thankyou for your responses.

The sheeps foot roller was kicked into me as an 18 year old in 1968 and still applies today. For compacting side fill compact ALONG the slope on a flat bench. With each lift ensure that you cut into the natural ground and mix that material with the imported fill and start the fill at the lowest point.

Tones said:

The sheeps foot roller was kicked into me as an 18 year old in 1968 and still applies today. For compacting side fill compact ALONG the slope on a flat bench. With each lift ensure that you cut into the natural ground and mix that material with the imported fill and start the fill at the lowest point.

Click to expand...

That's a totally logical approach. I think I'm going to try that method. Sometimes there's so many options out there that it gets overwhelming. Thanks mate

divo247 said:

That's a totally logical approach. I think I'm going to try that method. Sometimes there's so many options out there that it gets overwhelming. Thanks mate

Click to expand...

I've never seen anybody use a sheep's roller on residential construction. For one, it's a big no no next to a concrete basement wall. Unless you want it pushed in!

skata said:

I've never seen anybody use a sheep's roller on residential construction. For one, it's a big no no next to a concrete basement wall. Unless you want it pushed in!

Click to expand...

I was thinking to compact the embankment side with fill, the soil will have some clay and gravel. the sand pad for the house was gonna roll with a double smooth drum roller.

Pictures divo, we need pictures !