Replies

1. 
   James_Dahl | Oct 25, 2000 09:36am | #1

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   Greg

   Here in north central New Jersey, we have many areas with clay soils sitting on top of fractured shale. The water pops up all over and does not like to go back down.

   Curtain drains. We call them wick drains. 8-12 inch wide trench. One to three (depending on the flow) 4" diam Poly/PVC perferated pipe (the black and white stuff). Holes go down. Don't use corrogate ABS. It is fine for sone areas, but it holds clays, silts and every piece of debris that gets in. ABS also crushes under the weight of settlement.

   Make sure you have adequate slope on the trench. You can actually take water away from one problem spot, only to create another one elsewhere. If you have to cross the drive, use solid pipe so you don't let the water out.

   After the pipe is in, we fill it to the top with 3/4" clean stone. No fabric. Our clay soils clog the fabric in a matter of months, and the face of the fabric becomes a dam, and the whole process becomes a waste.

   If you have sandy soils (but then why the concern?) fabrics will help to keep the smaller grains from running into the drain and pipe and prevent long term settlement. But if there is any clay or silt, don't do it.

   The frost line has never been a problem, except in some cases where the drain daylights and there is constant flow - a trickle is worse than a good flow. We prefer to add a little slope at the end to ensure the water does not stand up and freeze so readily. Often, the warmer subsurface water (45 degrees) actually helps keep the outlet free of ice buildup.

   Don't worry about the surface of the stone. Grass will naturally fill over the gravel. Grass likes to do that. It will burn in the summer to some degree. But if that doesn't sit well, this is where you use the fabric. Six to eight inches down, lay the fabric on top of the stone and soil away. Fabric will keep the surface soils from clogging the stone.

   As far as depth - your property - your call. You have to get deep enough to catch the subsurface water that you fear will be problematic. Water goes where water wants. I have put drains on shallow slopes 4 feet deep, yet the spongy area 15 feet away is not relieved.

   The driveway area needs attention before you pave. Make sure the subgrade is firm and evenly sloped equal to the final grading. That means positive slope to drain water away.

   Drive some loaded tandems over it and look for pumping of the surface. Pickups are not heavy enough. If any spots are soft, dig them out and fill with blend, properly compacted. Or better yet, make the drive contractor responsible for that. Ha!

   If any of the drive areas are currently spongy due to water, wick drain these now, before you pave, and give some time for settlement if you can.

   Jim
   dahlpro.com

2. 
   greg29 | Oct 25, 2000 09:36am | #2

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   I have to put a curtain drain, so that water does not drain under my new to be paved driveway. Whats the best base to use gravel or process, I'm going to put filter fabric over the perforated pipe. The frost line where I live is 38 inches. Thanks for the help.
   Greg