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Long concrete driveway Chuck 11-15-2006
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Posted by Chuck on November 15, 2006, 4:16 am
Hello,
sorry for posting another driveway question - a few have been answered
pretty thoroughly in the past couple of days.

This question concerns a driveway/private road that I'm going to build on
a steep(~20%) grade about 675 feet long. The current plan is to use two
3' wide strips of concrete 4 inches thick for the driving surfaces leaving
a 26" open span in the center(or possibly covered with a sheet of thin
concrete to prevent erosion). The reason for this design was price is and
has been a stumbling block. So my first question would be, do these
dimensions make sense and second, what do you think of the idea of going
with two strips of concrete on a steep hill? Is that going to be
problematic?

Another thing we need is good drainage and the drainage probably needs to
cross the road at some point. Any ideas? As for the soil all this will
be resting on, the best I can describe it is a rocky red clay.

Any input will be greatly appreciated,
--
Chuck

Posted by kickstart on November 15, 2006, 7:39 am
> This question concerns a driveway/private road that I'm going to build on
> a steep(~20%) grade about 675 feet long. The current plan is to use two
> 3' wide strips of concrete 4 inches thick for the driving surfaces leaving
>
> Another thing we need is good drainage and the drainage probably needs to
> cross the road at some point.
> Chuck

driveway should be 5-6" thick
Drainage should go under(culvert pipe) rather than over drive



Posted by Chuck on November 15, 2006, 12:46 pm
On Wed, 15 Nov 2006 12:39:06 +0000, kickstart wrote:

>> This question concerns a driveway/private road that I'm going to build on
>> a steep(~20%) grade about 675 feet long. The current plan is to use two
>> 3' wide strips of concrete 4 inches thick for the driving surfaces leaving
>>
>> Another thing we need is good drainage and the drainage probably needs to
>> cross the road at some point.
>> Chuck
>
> driveway should be 5-6" thick
>
OK. It's a bit of a maze but I think I can keep it between 5" and 6"
without price becoming prohibitive.

> Drainage should go under(culvert pipe) rather than over drive
>
Ah, which brings up a good point. We had a culvert pipe about 14" wide
get clogged a few years back. Now it's solid from what I can tell. If
I'm building this with two slabs of concrete, can I simply make the side
culvert cross under the road, albeit a bit deeper and make the slabs
thicker(maybe 8" thick with 2 pieces of 1/2" rebar) where they cross as
bridges? The bridge span would be about 3 feet and I'd have plenty of
room to clear debris this way.

Thanks,
Chuck

Posted by Chuck on November 15, 2006, 12:24 pm
On Wed, 15 Nov 2006 15:43:34 +0000, Bob Morrison wrote:

> In a previous post Chuck wrote...
>> This question concerns a driveway/private road that I'm going to build
>> on a steep(~20%) grade about 675 feet long. The current plan is to use
>> two 3' wide strips of concrete 4 inches thick for the driving surfaces
>> leaving a 26" open span in the center(or possibly covered with a sheet
>> of thin concrete to prevent erosion). The reason for this design was
>> price is and has been a stumbling block. So my first question would
>> be, do these dimensions make sense and second, what do you think of the
>> idea of going with two strips of concrete on a steep hill? Is that
>> going to be problematic?
>>
>>
> A 20% grade is very steep. The transition grades at top and bottom must
> be well thought out or you will be dragging the bottom of the vehicle on
> the ground. Also, I hope this driveway isn't located where it frosts or
> snows. During cold weather most normal vehicles won't be able to get up
> or down it.
>
Thanks for the reply,
I didn't really refer the the grade properly. Thankfully, it's not all
20% grade and it's certainly not at the beginning nor at the end, but a
few sections in the middle are very steep. The weather is tropical so no
there is no frost/freezing but it is near the beach so I think I'm
considering not using metal(thanks Bob). My rational is that not using
reinforcement will be cheaper and there will be no chance for it to rust
which on a thin slab with so-so drainage and hand mixed concrete seems
likely.

> Slab thickness should be at least 5 inches. Skip the thin slab in the
> middle. It will just break apart and be unsightly and perhaps even
> dangerous. You could think about using plantable pavers (grass-crete).
> However, I think that you will find that the cost of doing anything but
> pouring a uniform thickness unreinforced slab will be higher.
>
OK, 5" and no center slab. How about the road dimensions. Is there a
standard for double slab roadways like this? I came up with those
measurements (two 3' wide strips 26" apart) by getting under the car with
a tape. I'm not really sure how much other vehicles may vary.

Is every sixty feet OK for expansion joints and would you have any
thoughts on what type of prep work I will need? Keep in mind I'm doing
this in a small town in South America and we don't have any heavy
machinery available. It will be done with a pick and shovel and a LOT of
patience.

Chuck

Posted by Bob Morrison on November 15, 2006, 1:03 pm
In a previous post Chuck wrote...
> Thanks for the reply,
> I didn't really refer the the grade properly. Thankfully, it's not all
> 20% grade and it's certainly not at the beginning nor at the end, but a
> few sections in the middle are very steep. The weather is tropical so no
> there is no frost/freezing but it is near the beach so I think I'm
> considering not using metal(thanks Bob). My rational is that not using
> reinforcement will be cheaper and there will be no chance for it to rust
> which on a thin slab with so-so drainage and hand mixed concrete seems
> likely.

I have used GFRP reinforcing in elevated slabs in tropical climates, but
it is expensive. So, I think going unreinforced is a excellent idea.

> > <snip>

> OK, 5" and no center slab. How about the road dimensions. Is there a
> standard for double slab roadways like this? I came up with those
> measurements (two 3' wide strips 26" apart) by getting under the car with
> a tape. I'm not really sure how much other vehicles may vary.

Compact car parking spaces are often 8 feet wide. This is probably a
little narrow for a driveway, but if the driver is at all decent, 8'-6"
could be okay. I'd probably go no less than 9 feet minimum to allow for
the occasional small truck or delivery van.

> Is every sixty feet OK for expansion joints and would you have any
> thoughts on what type of prep work I will need? Keep in mind I'm doing
> this in a small town in South America and we don't have any heavy
> machinery available. It will be done with a pick and shovel and a LOT of
> patience.

End of pour cold joints can be 100 feet apart or so. This kind of joint
will be full depth and will have a shear key and some oiled dowels to
transfer shear across the joint. Crack control joints should be every 12
to 15 feet. These joints are usually tooled or sawcut and are 1" deep.

For hand mixed concrete you will probably not be able to pour more than
9'x 14' in a day. So, it won't be necessary to cut crack control joints,
but you will need some method for transferring shear between one day's
pour and the next.

For compaction of subgrade, use a loaded dump truck or other heavy
vehicle. For compaction of gravel base see if you can rent a Jumping
Jack. If not then you can run the heavy truck over the gravel and use
hand compaction methods for as needed.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

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