Blacktop driveway doesn't like winter

[Ray K.]

After extended periods of subfreezing temperatures (central New Jersey), the top of my blacktop driveway raises about 1.5-2.0" above the level of my garage's concrete floor. (In warm weather, the two surfaces are flush.) So when I drive into the garage, the weight of the car literally "snaps" the blacktop at the junction. (Yes, this suggests a void or inadequate support under the blacktop.)

I'm not sure how water gets under the blacktop. The soil is clay; the attached house is on a concrete slab. Gutters are working properly to carry rain away from the house and garage.

At the rear of the 200-foot deep lot, the soil has a 17-degree slope toward the house and garage. (The length of the slope, not its height, is about 30 feet.) The distance from the foot of the slope to the back of the house and garage is about 30 feet; the distance to the front of the garage and the start of the blacktop is an extra 30 feet. Perhaps rain from the slope is oozing under the garage slab and making its way to the driveway. (Only once in four years has any water made its way into the living area, and that took place in the laundry room that's behind the garage. So it seems like the water path is right under the garage. But since their is are no wall cracks, the garage itself doesn't appear to be raising, unless at the same rate as the whole house.)

The seal where the blacktop meets the garage floor is poor, but the 20" roof overhang and its gutter keeps most rain out of the gap. Another way for water to get under the blacktop is where its edges meet the surrounding lawn.

There is also a very mild slope of the driveway down toward the street. The driveway raises most within 20 feet of the garage, and virtually not at all 100 feet away where it meets the sidewalk/street.

I'm planning to replace the driveway in a few weeks. Questions:

1. If I stick with blacktop:

a. Should I make the depth of the gravel under it extra deep to provide better drainage? What depth? (One contractor proposes 6" of crushed concrete, called r-blend.)

b. If the new depth is greater than existing depth, all existing gravel must be removed. Should I allow the contractor to reuse existing gravel?

c. What's the best material to use under the blacktop? As noted above, r-blend is standard in this area, but I'm not sure it's best for my situation.

d. Should the thickness of the blacktop also be increased? To what depth? (Same contractor proposed 3 inches.)

e. Any other options for improving drainage?

1. Another approach might be to use a "porous" top, like paver bricks. Yes, this will allow more water to get below it, but when the soil freezes and raises the driveway, no lasting damage will occur when I drive into the garage. Does a porous top make any sense?

(To reply by email, remove the xxx from my address.)

Thanks,

Ray

[m Ransley]

could drain tile be worked into your lot ?

[Ray K.]

[Joseph Meehan]

...

it sounds to me like it should be deeper busy no reason you'll gravel cannot be reused

Usually what is standard in your area is best for your area.

Your problem is most likely due to the base and not the blacktop this should be no need to increase the thickness of the blacktop .

I personally like the looks of papers and I like the fact that they can be repaired but they also are usually more expensive and generally require repair sooner.

[AJScott]

Your clay soil explains a lot, even with proper gutters. In addition to being the worst drainer of water in the world, it's one of the world's finest retainers of water. What it gets, it keeps for a good long time. Therefore, it's entirely probable that once the clay is saturated, snow and rain water is being carried just under the surface (or deeper) along that grade/slope pointed at your driveway. Also might explain your cold-weather heaving of the driveway surface. Since clay retains a lot of moisture, all that moisture has nothing left to do but freeze and cause all sorts of headaches much like yours.

Unless there's great drainage for a considerable depth beneath the driveway sub-surface itself, you'll just be allowing even *more* water to get down to the clay with pavers and, well, if you think you have problems with one section of solid asphalt now, wait until you have to start re-setting a mess of pavers popping up along the whole length and width of your driveway.

One easy solution, relatively speaking (since you're going to end up spending money anyway) is to have a contractor install a French Drain (or if you're incredibly handy, you can DIY it) to carry/drain off the water before it reaches the driveway, idea being that water can't screw up things it can't reach in the first place.

Or, digging up a mess of ground around the driveway several feet wide and a few feet deep and replacing the clay with a soil that drains significantly better would be another measure to try before considering having to touch the driveway itself.

AJS

[L. M. Rappaport]

On Thu, 19 Feb 2004 15:36:34 GMT, "Ray K." wrote (with possible editing):

Your problem is almost certainly the clay. The house won't move because it's heated so frost won't get under it.

You need to remove all the clay down to the depth of frost penetration.

If there's gravel there, it doesn't need to be removed providing it doesn't sit on top of more clay. Gravel drains well, that's why it's perfect fill. I'd allow him to reuse it so long as it isn't mixed with clay.

Gravel works well. Your local contractor should know what's available and reasonably economical.

I don't know. I'm GUESSING that it wouldn't make a lot of difference since frost can heave runways and highways which are a lot thicker. The key is to remove water and to prevent it from getting in there.

Drains as others have suggested, but you must get rid of water in the freeze zone.

I wouldn't do it. You'll never get them reset correctly in the Spring.

[Ray K.]

Hi AJ,

Thanks for the reply.

The driveway needs replacement anyway, so I can't save that expense. Both your ideas sound good; I'll investigate them. I always look to the future and believe an ounce of prevention now is worth a pound of cure later.

Ray

AJScott wrote:

[AJScott]

Since you're replacing it anyway, you might want to consider eliminating as much clay beneath the driveway itself with a deeper than common layer of gravel (or a sandy-loamy soil mix) to provide any migrating water better drainage, since gravel and sand and loam drain well.

AJS

[Ray K.]

Thanks, LMR, for the additional analysis and suggestions.

Ray

L. M. Rappaport wrote: