Spongy Driveway......

[Dennis Peacock]

I have a dirt and gravel driveway. It is supposed to be an old road bed from what would have been a street to a back section of a subdivision, but the builder stopped building houses and the old road stops at the back of my property.

With the current building project of adding onto my house, I've had 4 concrete trucks in here and multiple lumber supplier trucks in here with more to come. My driveway is great from the street to about half way back towards the house and then it starts to be torn up by the trucks and up closer to the house it's not only torn up but is also spongy....if I walk on it, I can get it to move up and down as much as an inch. It's like walking on top of a suspended bridge in a way. :)

Can anyone here tell me what is really my problem and how to fix my driveway? Please advise.

[Chris Parks]

My experience with that problem was a high level of water under the area, a spring perhaps?

[Dennis Peacock]

Chris,
Our area has a high water table anyway. It's never been this way before but super heavy loads like full concrete truck have a tendency to find your weak spots in the driveway. I'm just trying to sort all this out so I can figure out how to best fix my driveway. :)

Oh....and we've been living here for 14 years now.

[Matt Meiser]

Whatever you do, don't add large stone on top of small. I pull the large stone we added to a soft area up CONSTANTLY.

[Ole Anderson]

Sounds like a high groundwater table combined with clay or silty soil. Common solution is to dig out about 8-12" of bad material, lay down a geotextile material, followed by 3/4" crushed stone or crushed concrete. The geotextile keeps the large stone from being pushed down into the finer material, and conversely, the fine material from working its way up into the stone.

[Dennis Peacock]

I'll try and take pics tomorrow and post them.

[Lee Schierer]

If you lived further north I would say you are experiencing ground thaw heaving. It is pretty common around here for roads and driveways to get spngy in the spring as the ground thaws out. This year more than most due to the extended cold weather we had.

[John Conklin]

What I've seen under roads where there's soft spots in the sub-base is to excavate down about a foot, put down geotech fabric then large rock (fist size) then a final layer of base (3/4" and less). The geotech fabric is about the size of welded wire fence, but made out of a heavy duty plastic. It makes the layer of large rock work as one structure and helps span across soft/wet areas. This was 15-20 years ago so I imagine there's better/newer ways by now.

[Fred Perreault]

What John and Ole said..... here on the Cape we have varying strata of soils from the glacial formations we are composed of. Where there are clay deposits they can hold more moisture than the sandy, coarse materials that we mostly have. When heavier traffic travels over the clay areas during wet periods, it softens the ground by bringing the water closer to the surface. The soil remains solid but "spongy" (plastic, or elastic) as you mentioned. Eventually you can bring the moisture out through the surface and the next phase is a rutted, muddy mess. There is no way of knowing the depth of the clay without digging a test hole, or boring with an auger or post hole digger. Excavating down to a reasonable depth (1'-2' minimum) for the intended traffic and then using the geotextile and a gravelly local material would improve the situation. But the flip side is that if clay is the problem, then doing this can create a situation where the repaired area can actually hold water, as what is being done is to make a base for the drive that drains water on it's own, but being on and in a clay pocket it has no where to go quickly as the clay is a semi-pervious, slow draining soil. The water will eventually percolate through the geotextile and down into the tighter clay soil, but in the meantime the roadbed might be somewhat rubbery depending on the weight of the traffic. But with the new base material there would be virtually no chance of rutting and sinking out of sight. We use the geotextiles (there are variuos weaves) frequently, especially when building stone walls/revetments/seawalls as it permits water to pass through but keeps the soils in place as they cannot pass through the tight fabric. It might be worth the expense of improving the roadbed, unless what you are experiencing is a very rare occurence.

[Tony Zona]

My driveway was very spongy, especially in wet seasons. It turned out that I am extremely fortunate there is a slope from the house 600 feet to the road.


What I installed was what some call a French drain in the clayish, silty soil. My highly skilled excavator operator dug a one-foot-wide trench along side the driveway and made sure the slope would drain. The trench was six feet deep at one spot, and as little as two feet at the road.


Over coffee one day, an engineer friend advised me to install laterals every 50 feet. I did. Each lateral spanned the driveway on a downhill angle.


Here's how the drain itself was built. Geotextile material was laid in the trench, with material on both sides of the trench long enough to extend above the furnace. At the bottom, we put on about three inches of gravel into the material. We laid flexible, corrugated, perforated drain pipe on the gravel. Then covered the pipe with gravel to nearly the top. Fold the geotextile over the gravel. (Think burrito.) Cover the material with a couple inches of soil.


Same with laterals, but cover with driveway gravel.


The first wet season we were rewarded with a solid driveway. We could see the end of the pipe entering the sewer. Water was flowing the full four inches that first spring. It has worked wonderfully for the past 15 years.


As you can see, nothing here is new. Also, I'm convinced the laterals have helped greatly to dry the driveway. Previously when a car, or especially a delivery truck, drove up, the tires would sink an inch or so and the soupy driveway would slurp back and forth. Not any more.