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MWM 08-01-2004 01:09 PM

We are working on a raised patio project and need some help. The project includes removal of an existing wood deck, using a segmental retaining wall system to retain the elevation changes and build steps then installing pavers. I have two questions:

1) Beneath the deck they had used clear limestone gravel a couple of inches thick I would assume for weed suppression. We will be raising the area anywhere from 12-18" with compaction gravel. Does the clear gravel need to come out? Or can we regrade, compact and cover it with a geotextile to keep the two gravels seperate?

2) As part of this project the homeowner wanted a sleeve installed beneath the patio and walls in case his water line ever needed replaced. The home builder has this completed but not backfilled. Should the trench be filled with clear gravel or compaction gravel?

Edit:This discussion has been included in the site beginner's brick paving page.

Rex Mann 08-01-2004 02:32 PM

The clear gravel under the deck is OK. However, if the soil under it is topsoil it needs to be removed.

The trench should be filled with compaction gravel and then mechanically compacted NOT WHEEL ROLLED.

As for the patio infill and its composition, there are many schools of thought on how to go about this task. Some may say to use clear stone most of the way up your retaining wall to allow for drainage. Then use a 4-6 inch lift of compaction gravel on top of that. Between the 2 layers you would place a geotextile and also on the sub-soil.
This school is based on the assumption that pavers allow a great amount of moisture to pass thru their joints and peculate into the base material below.

Another school of thought is using all compaction gravel as in a traditional paver installation with a geotextile underneath.
This philosophy is based on the knowledge that pavers are not as free draining as most people think.

Currently the ICPI is creating a specification on raised patios. Their construction committee will be discussing it at the summer meeting next month.



PSUscaper 08-01-2004 07:04 PM

I wouldn't of been real happy with that sleeve going in. Considering it is going to be 4 ft deep.....I'd imagin they just dug a 4 foot trench that cuts right through the middle of your entire project.

Gonna be very tough to get 100% compaction in a deep trench like that. Almost need a sheeps foot to really do the job right, or many, many layers of compact and fill.

I've just always been nervous building anything on top of a freshly dug excavation.....especially if you were not the one to do the work.\

we all know what happens when they cut a road open to put a water main line get a 2 ft wide 'tire rut' going right down the middle of the road when the asphalt you may have that right in the middle of your wall.

Bill Schwab 08-01-2004 07:17 PM

WE always tie all sides together using Geo-Grid (Stratta Grid 300) when we build a raised patio. In areas that freeze, it will hold all the sides together in case water locks inside. I like the use of clear gravel throughout the patio, with fabric over the top to prevent the sand from sifting down into the voids. If you place a 3 or 4" sdr-35 perf pipe in back of the wall, and tie it to an underground drain or daylight, there will be very little chance of settling.

If we open any trneches under where footing will go, we use a Wacker jumping jack style compactor in the trench and try to get as close to 100% as we can. Any pipe that runs under the wall is sleeved with schedule 40.

Paul 08-01-2004 07:22 PM

I agree with Rex on the removal of the topsoil under the patio and backfill the trench with the 3/4 gravel. It would be done in 4" to 6" lifts. Now I'm not going to get more than 85% compaction on it but I know it won't move.

As for the raised patio standard 3/4"- (Ca-6) would be used, unless there are water issues from surrounding areas, such as a hill that meets the patio. Then a standard 3/4" washed gravel gravel with a fabric backing lapped over the last 6" of wall to seal off the fines migrating.

I do have a question for all here.... has any one had a major repair done thru a raised patio? Like a water line? To me it would seem more likely to have a sewer line to be repaired than a water line. If they where going thru all that I would have them sleeve both lines.

MWM 08-02-2004 05:33 PM

Thanks for the replies.

I will be interested in seeing what the ICPI comes up with as far as recomendations for raised patios as we seem to be getting alot of this type of install.

Paul - I guess I wasn't clear with the entire purpose of the sleeve. The homeowner has a well. The water line runs beneath the area we will be working in. He has already had to replace the wiring to his well pump and doesn't want to seal off his options in the event it happened again. There are no other utilities in the work area.


BRL 08-05-2004 07:24 PM

I have had my well water lines break 2 separate times, separate places, in separate years, so I would agree with putting a sleeve on it.

I have a question for everyone. I have seen a few people mention "clear" gravel in this thread. One person or one or 2 uses of the word & I would assume this to be a simple typo. But with so many using it I am wondering what this is? My suppliers call what I would use for that described situation "clean" gravel, meaning it is that size gravel with no dust or small pieces of the stuff mixed in, like would be for a compaction type gravel. I have also seen "clean" gravel used in various web sites & literature from various SRW, and concrete paver companies. So is there another product out there called clear or is that the same thing I know of as clean ( I know we've learned many examples of regional differences in what certain materials are called from these discussions, so I was thinking this might be another example)? Thanks.

Paul 08-05-2004 08:56 PM

There are a number of different gravels that you can call "clear" or "clean".

Washed river gravel has a rounded surfaces and can't be compacted. Crushed, washed gravel has angular surfaces that allow compaction, but less than you could achieve with fines. When you get to larger walls with higher loads a washed river or rounded gravel would cause problems. Where as the crusher run washed will hold the load but not show the 95% compaction that you would like to see with a stone that has fines.

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