Replies

1. 
   Guest_ | Apr 14, 2000 09:57pm | #1

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   Darrell,

   First of all why 2" to 4" rock. You trying to bridge a swamp? Large rock like this isn't meant to be compacted. It's supposed to "bridge" unstable soils. If you really need large rock, then cap it with smaller 3/4" minus crushed stone. Six to twelve inches should be enough. Make sure moisture content is high enough to reach maximum density without over wetting. Construct fill in 6" maximum lifts and compact with a vibratory plate tamper. (Heavier is better). Since you're working in a trench a "jumping jack" tamper will work also. The stone supplier should be able to give you a target density / optimum moisture (Proctor). Who ever checks it will probably use a nuclear densometer. This will give results in LB/C.F. and also a moisture content. 95% of maximum theoretical density will satisfy most agencies. If you don't pass, just keep packing. A lot has to do with who is checking also. Personally, I can go out on a prepared subgrade and just by looking around can find places that will pass and places that will fail. The "nuke" reads how much void space is present in the fill. The deeper the probe is imbedded the more accurate the result overall. This is probably way more info than you wanted but hey, its free!

   Eric

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   Darrell_Hambley | Apr 14, 2000 10:13pm | #2

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   Eric, Thanks for the info. I too, was wondering how I'd get that large rock to compact. The inspector pointed to the large rock I had layed for a driveway base and said "you'll need to fill a trench with large rock like that" The 3/4" on top makes a lot of sense.

3. 
   Guest_ | Apr 14, 2000 10:55pm | #3

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   Eric, in my experience, it is impossible to test 3/4" stone with a nuke, unless you put on the asphalt setting. (Troxler or Siemens). I think a good old fashioned cone test is what he would need, but from the advise he got from the inspector, I don't think the inspector really knows what he is talking about. Usually when I place 3/4" stone over( and of couse within the voids all the way down), it gets watered heavily and proof rolled until no sagging occurs. For a trench situation, I can't believe the inspector recommended the large rock.

   Years ago in my youth, I used to test soils, asphalt, stone, etc. Have you ever tried driving that probe thru crushed stone? Yikes!!

   And guys - take it easy here, be nice! ;p

4. 
   Darrell_Hambley | Apr 17, 2000 08:17pm | #4

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   Well, after escavatiing 2' this weekend we're down to good bearing clay. I've got no experience with engineering a compacted rock base so I decided it's going to be much less hassle to simply make my stem wall 4' instead of 2. The 2-4 rock which was delivered can be a base for the rest of the driveway anyhow.

5. 
   Guest_ | Apr 17, 2000 09:02pm | #5

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   Wolvie,

   When nuke testing stone you've got to get the probe into the material. The backscatter position is too heavily weighted toward surface voids. Our Troxlers come with a slide-hammer drive pin for making the test hole. Even on asphalt binder, a fill-coat of mineral fines is recommended to get a really accurate reading.

   Sand cone? Most people don't know what that is let alone how to use one! You must be r e a l l y old, huh? I bet you used a four screw transit too! ;-)

   Eric

1. 
   Guest_ | Apr 17, 2000 09:09pm | #6

   *Darrell,If your time is worth anything the additional concrete for the stem wall is much cheaper than placing and compacting stone fill. Plus, by the time you get the stone compacted to 95%, you can't drive your form stakes into it! You're learning . . .Eric

1. 
   Guest_ | Apr 18, 2000 11:09am | #8

   *Don't know what qualifies as really old, but probably!At the astm training place in Ohio, they made us use cones, water balloons, everything! ;-)Anyhoo - the penetration into asphalt used to be just an inch or so. Is it different now? Even with a drive pin I don't see how you can test stone - there is no way not to create voids when making the hole.And - using a four screw transit - yep! At UofM, they made us learn on the old stuff before we could use the new stuff. Don't know if that is still the case. Said something about computer chips gone bad, where would you be, etc. ;-)

6. 
   Darrell_Hambley | Apr 18, 2000 11:09am | #7

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   Per inspectors advice, I'm putting 2-4" rock in a trench which will be under foundation footings. This will be 2' deep, 3' wide. It has to be compacted to pass a stiffness test. I can rent a tamper but has anyone used some other method to compact rock? Thanks DH