What type of gravel?

Some good advice given here but Gary's advice is the most important, the sub-grade is the primary consideration when engineering a road surface (which is what this is in essence). If you have a sand bedding then just a couple inches of 3/4 crushed rock would suffice if well compacted. Sand is generally well drained and does not heave in the frost like a clay or loam soil will. A clay substrate will move the closer it is to the surface and needs to be removed below the frost line (depth at which the ground freezes).

If you have sand, just lay a couple inches of class 3 road base, level it out and compact and yer done.

If its clay or has high clay/silt percentage then you need to determine the frost line as determined by your local climate. 6 to 12 inches should do it unless you live in North Dakota or someplace subject to long cold nights. You will want to lay a couple inches of sand down to act as an insulator between the clay sub-grade and rock base.

A true road base material such as the class 3 (a Cal-Trans standard YMMV) has all crushed rock with many fractured faces that is specifically graded by percentage of weight by volume or whats called a gradation. You want a variety of sizes of aggregate to get a solid section. bigger rocks, generally 1/2" sieve to 3/4" to add weight bearing and longevity and then there is varying size smaller bits to fill the voids between the larger bits.

Every state highway department has standards for road base and any material supplier will have a supply of it on hand. Don't ask for "half inch rock" tell them you want road base.

I've been inspecting this poo for twenty years.

ETA: a vibra-plate compactor will work fine if the lifts are only a couple inches and you have plenty of moisture.

Rockhound knows whats up.

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My landlord builds driveways out in the sticks, he uses ~6" of road mix directly over clay.
He also said you need the mix over the clean stone like Rock said???
Our parking lot is 12", but only because he has semi's & bulldozers coming and going all day that weigh 10's of thousands of pounds each.


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Big tip that can save you hours in placing the material: Most decent truck drivers can lay it down at a fairly even surface with proper spotter. Don't have him dump it in one pile and try to move it around. Have him back into it, crack the gate, lift the bed and pull forward spilling an even layer over the surface. The speed and tilt of the bed will determine the thickness of the layer or "lift" then you level and compact between each load.

 

every spring I'd get a yard of 2B stone ($25/yd) in the bed of the Superduty & spread it into the low spots of my gravel driveway

this year I picked up two yards on the trailer as the '15 Chevy is a girls truck

 

Hooters girls come out and spread the gravel for you?

 

Superduty was an 8 foot bed with helper springs

2015 Silverado is like a 3 foot bed with what seems like one leaf

 

I put a foot of CA-6 in my driveway widening with plans to be able to scrape off up to half of it to pave later. I soaked it sopping wet with a hose and ran over it with a small vibratory plate compactor - they rent cheap. It packed in so tight, there has hardly been any change in the last 8 years.

 

We have loamy sand here in Brighton, with about a foot of top soil(they used to grow corn on it). The excavating guys that put out driveway in said they needed to remove all the top soil, and then they filled it with just "road gravel", which I recall is 21A. It's crushed rock with some clay mixed in, and supposedly over time the clay sort of "locks" the gravel in place. But the gravel should have sharp corners, from going through a crusher - not just rounded stuff directly scooped from a gravel pit. It's the same gravel the County grade our dirt roads with.

Some people put a crushed rock "finishing" layer on, which I believe is called 22A around here. Very little clay in that.

For problem areas around here, where the driveway keeps sinking, I've seen people lay 3" stone down, limestone I believe. Then the road gravel over that. But we haven't needed that.

 

They can pack it down too if you provide them with the tunes they like.

 

Google soil cement and do that yourself. Most airplane hangers have that as their floor . it'll be fine for your use.