Optimal patio pad preparaion ? Soils, compactors, methods...

[someguy11]

I'm building a 20x45 foot patio in front of my house. The patio surface will be paver blocks or something similar, ie not concrete. I need to increase the elevation of the area by about 1 foot to reach the proper grade for the patio.

The main floor of the house sits about 2 feet above grade. We'd like to have 2 steps from the main floor down to the patio. With a rise of 6" per step, the patio grade will be 12 inches below the elevation of the main floor. This means we need to increase the elevation of the pad area by 12 inches to reach the proper grade for the patio.

I plan to put 3" of crushed rock and an inch of sand beneath the paver stones, meaning I need to build up the base dirt by 8 inches.

We removed the existing concrete steps and pad in front of the house. We removed the pilings that were under the concrete steps. We removed the sand/gravel that were placed below the steps. We stripped the top soil and sod from the area and removed any lose/organic dirt until we were down to hard clay or hard gray dirt. The house was built 6 years ago so all the dirt around it has fully consolidated.

We obtained 3 different soils to raise the elevation.

The first was a pure clay, dug from around a house foundation by my neighbor while he was fixing drainage issues on his house. This clay has no rocks and no significant lumps.

The second soil was similar to the first, but with a bit more sand in it. It is like a silty clay. It too came from a house foundation excavation.

The third soil was supplied by a landscape soil supplier. It is described as an "engineering or structural clay". It is a very hard clay, lot of big lumps that can barely be cut with a sharp shovel and also, unfortunately, quite a few stones and rocks, from 1" to 4".

We began by placing thin lifts (1-2") of soil #1 (pure clay) on the undisturbed soil around the house. It was moist from getting rained on while sitting in a stockpile. We compacted it with a 500 pound vibrating plate compactor. It got quite hard and seemed to work well.

When we ran out of soil #1, we started using soil #2, a siltier clay. It did not compact as well as soil #1, so we stopped using it.

We started using soil #3 as soon as it was delivered to the site. The first problem is the lumps, some as big as 6 or 8". Very hard to break up, so you can't apply a 2" lift and have the plate tamper consolidate it easily. The second issue is the rock and stone in it. We've been ignoring the stone that is less than 2" and the rest we've been throwing on a pile. I complained to the supplier that the supplied soil had too much rock in it, but he said he has been in the landscaping business for 30 years and there was nothing wrong with having rock in the clay.

Individual lumps of soil number 3 will compact to be very hard, but the lumps don't bond with the soil around to make a plastic soil. We've tried adding more water, etc, but it doesn't seem like our plate tamper has enough vibration muscle to make a homogeneous, plastic clay from it.

I know that a plate tamper isn't the best for working with clays. I thought a bigger variant (500 pounds) would be more effective. Will a jumping jack rammer be much better ? Should we rent a padded drum vibratory packer ?

I'm uncertain how to proceed. I suspect we have 4" of clay #3 that isn't totally consolidated. I think I want to strip it off. Is clay #3 really the best clay for this job ? How would you deal with the rocks ?

How exactly should one build an optimal patio pad ?

Thanks

 

[someguy11]

The entire pad is encased down to the original grade by curbs or retaining walls. Weeping tile is strategically placed under the pad.

Why am I even trying to use clay ? Why don't I use a sandy soil with some clay in it ? It will be easier to place, drain well and won't swell if it does get wet ?

 

[DougWil]

I would talk with a geotechnical firm in YOUR area. They will know what is the local preferred fill.

In general clays are not the best sub base, especially since water will be passing through the joints in your pavers.

 

[matt_i]

What I would do is source a geotextile fabric to keep the crushed stone base from getting smashed into the clay. I hate clay but its here, rock hard when dry and like stinkless baby poop when saturated with water.

One of the best things I think you can do is build a 1/8" per foot or so slope into your patio to promote runoff. Not sure of your location and thus if frost heave is an issue or not. The good thing is that the block can be "reset" in spots if there are issues.

 

[someguy11]

The clay base and the patio itself has a slope of 4" in 20 feet - 1/5" per foot. We are also going to put weeping tile into the surface of the clay, beneath any sand we use to try to keep it dry.

Having said that, the undisturbed soil is pretty stable, even when wet.

I forgot to mention that we are building the patio around 2 mature trees. We'll be covering their roots except for a circle around the trunk about 6 feet in diameter. We'll be watering them through the circle as well.

The patio surface will actually be flagstone.

The patio is being built in a northern climate, so frost is an issue.

 

[theoldwizard1]

... This means we need to increase the elevation of the pad area by 12 inches to reach the proper grade for the patio.

Here is what I would do

• Remove sod and top soil/loam (anything that contains organic material).
• Place heavy waterproofing up against the hosue.
• If you have fill, use it, but no more than 6 inches.
• The next 4" should be well compacted "sharp" gravel, like 3/4" crushed limestone or crusher run.
• The last 2" should stone dust/slag or what ever they call it in your area.
• Place paver on this.

 

[LXCam]

Since its all contained I'd just use sand. Compaction is everything and it won't swell and heave like clay based souls. Rock is great but unless you contain it like suggested will settle into the sub base soil as well as allow any top soil or sand to sift into it.