Steep Driveway Question

[ckissick]

I'm looking at a newly-built driveway that was built too steep. (The driveway goes DOWN to the garage.) The garage was supposed to be at 282.5 foot elevation, but was built at 280.5 feet. Now, the driveway is too steep to get a car in the garage. (I was hired after construction to fix the problem created by someone else.)

Long story short: If the driveway is 20%, and I want a 2% grade in front of the garage, what should be the vertical curve radius between the two gradients to avoid scraping a bumper? I can only find discussions on designing vertical curves based on the speed of the car and line-of-site distance - these don't apply here.

 

[WL123]

I would get a couple of specs. on typical car dimensions, large and small. Draw a template, and see what works on the profile. Draw both to the same horz. and vert. scale.

Sounds like its a tight situation, can the garage be jacked up if necessary?

 

[ckissick]

I've done that before with a fire engine. I was hoping there was a standard rule of thumb.

As for jacking the garage up, it has rooms above it. The only way would be to demolish that whole part of the house and re-do the roof. The builder took a lot of short cuts in building the house, making for a bunch of other problems. Lawsuits are pending.

 

[WL123]

Can you have the driveway enter into a different side of the garage?

Could the whole house be jacked up without messing up the front entrance?

Do you have a cad or pdf file, could take a quick look at it.

 

[civilperson]

The scale template idea will work if the model vehicle is created with the correct overhang from the wheel center and clearace. (Detroit unmodified vehicles use a 15 degree wedge for clearance from the tire/pavement intersection.

 

[PELS]

What is the length of the driveway? If it is sufficiently long, you can work with it to fit a curve between the front of the garage and the rising portion of the driveway. But if you have a short length, the radius of the VC won't matter and the solution may end up being quite expensive (as in "Reconstruct the garage slab to a higher elevation").

 

[bob3306]

I wouldn't think of it like a vertical curve with a radius of curvature, but more simply as series of grade breaks.

Divide the driveway up into several segments. Set the grades as you'd like at the end segments, and then work your way back to the middle from them and see if you can make it work. I try to limit grade break difference in driveways to 9% max for crests, and 12% max difference for sags. It may take a couple of iterations. Trouble is some segments will need to be over 20%... hope it doesn't snow there.

How were you planning on handling drainage? You could put a little valley gutter with a slot drain in front of the garage door.

Send the length and end to end elevation change and I'll give you a more detailed suggestion.

 

[ckissick]

Thanks, bob3306. The driveway is 100 feet long, but it splits off another driveway that goes next door. I can make it work using segments like you describe. It never snows here, so 20% driveways are somewhat common.