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Redbear
09-30-2005, 11:27 PM
Just started a job, 700 sqft driveway. In a heavy clay soil. Driveway was previously asphalt so we removed that along with 15 inches of previous base and clay to provide a 12 inch gravel base. Put in 2 loads now up to about 8" of compacted base, the water seems to be moving up into the gravel. The base is spongy under foot and only another 4" of base remaining to put in. Suggestions. I'm thinking I have to go down another 12 inches or perhaps more, but how far do I take it and is there anything else that needs to be done.

bigviclbi
09-30-2005, 11:50 PM
Dig a test hole near the driveway and see how far down the spongy soil is instaed of digging up the whole driveway.

Drafto
09-30-2005, 11:50 PM
This might be a stupid question but did you compact your subsoil at all before putting in your base? Sometimes you can force the water out by compaction, or you can let the soil dry out a little then compact. These are obvious things to some, but I just figured I would ask.

Dan

Redbear
10-01-2005, 12:00 AM
Tested a few areas in the driveway and no I don't see that all will have to come up again but about 1/3. Test holes showed that I would have to go down about another 15 inches. Does that seem practical.

Subsoil was compacted before hand with diesel plate compactor, being clay should I have used a rammer instead or does it matter much?

Drafto
10-01-2005, 12:06 AM
With clay a rammer is recommended. Did you use textile fabric? I had an experience once on a patio that had "pumping soil", you would step on it and it would still sink, even after the modified was in place. I ended up re-excavating it until I found suitable soil. Keep this thread at the top and I am sure one of the experts on here will help you, also try searching a little on the subject.

Dan

Redbear
10-01-2005, 12:14 AM
Thanks Dan, I did not use a textile fabric initially but when it is dug up again I will be using one.

DVS Hardscaper
10-01-2005, 12:18 AM
Remove the clay and replace with proper soil, such as a silt/sand type.

Compaction shall be done with a ride on roller.

If all that extra excavating is not possible...then they need a poured concrete driveway.

cgland
10-01-2005, 11:25 AM
Redbear - You need to excavate to suitable subsoil. DO NOT add any other types of soil to the excavation. The only thing goig into that hole is the base aggregate. You can try a couple of things. You could excavate another 12" and use portland cement to stabilize the soil or try rolling (vibratory roller)3A or larger riprap into the soil to firm it up. Definately use a geo separation fabric. It will help with stone migration and settlement if properly installed. You just have to explain to the homeowner that the soilis not suitable to build on and it will require some additional materials and labor. Doing it right the first time is alot cheaper than having to go back and tear it up. Hope this helps.

Chris

mbella
10-01-2005, 10:48 PM
Remove the clay and replace with proper soil, such as a silt/sand type.

Compaction shall be done with a ride on roller.

If all that extra excavating is not possible...then they need a poured concrete driveway.

DVS, why would you add soil and not stone?

Redbear
10-02-2005, 08:58 AM
I've returned to the driveway to see how things are now( 20 hrs later), all the water is out of the base and it is actually quite solid now. Guess all the tamping with 9000 lbs brought the water level up through the clay into base. What are your thoughts now, should I still excavate further or am I OK to carry on since it seems that the water level won't come up without the tamping? Thanks in advance.

cgland
10-02-2005, 02:40 PM
IMO, I would still remove the base, check the subsoil and install the geo- separation fabric. You know you have a water problem, and water does not flow up hill, so I imagine there is still some there. Better safe than sorry.

Chris

DVS Hardscaper
10-02-2005, 09:47 PM
DVS, why would you add soil and not stone?

I do NOT know why I wrote that, as that is not what I believe in (in terms of residential applications).

We NEVER ad soil as I recommended. We only build a base with 3/4" crusher run.

Although, you CAN add soil, as long as it is a suitable soil. And properly compacted. Its done all the time with highways and commercial and industrial jobs. But...the process is monitored by a geo-tech. For a small residential job as the one at hand, that would be foolish, making adding crusher run gravel the way to go.