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tlinate (Civil/Environmental) (OP)
12 Aug 09 10:45
Does 3/4" minus gravel base material meet the requirements of Section 4.5.1 of the ADA Standards for a "firm, slip-resistant surface"?  My client would like to build an ADA compliant pathway in his subdivision using gravel as the final top surface.
jgailla (Geotechnical)
12 Aug 09 13:02
You'll have to check with the AHJ (authority having jurisdiction) to see what they will allow.
I have a project under construction (north Florida)that was designed and permitted with a 3/8" minus (technically fine aggregate) crushed granite mix.
There was some discussion with the AHJ during design to get them to sign off on the crushed granite.
Ron (Structural)
12 Aug 09 13:41
A gravel surface is not stable and in my opinion, does not meet the intent of the ADA.  While ADA accommodates many forms of disabilities, the most commonly considered accessibility is that for wheelchairs.  Wheelchairs cannot negotiate gravel easily.  Further, walking on a gravel surface displaces the gravel and often displaces it beyond the 1/2" surface irregularity requirement.

I would not use gravel on an accessible route.

As jgailla notes, the AHJ would have local interpretation; but if you want the design to be fully defensible without local interpretation (sometimes erroneous interpretation), use a stable material for the accessible route.

Remember, the ADA is civil rights legislation.  It's dimensional and design considerations have generally been codified by inclusion in building codes; however, claims under the ADA are not building code issues...they are accessible rights issues, with interpretation often exceeding the bounds of simple building code requirements.
atook (Civil/Environmental)
12 Aug 09 14:46
I've used crusher fines for this purpose.

Tim Grote - The Irrigation Engineers.
www.irrigationengineers.com

Hoagie (Civil/Environmental)
12 Aug 09 16:27
I would add to Ron's ADA intent info with: an ADA surface should allow for a disabled person, particularly a blind one, to sense/feel a change in surface texture--the texture will alert them to a dangerous situation.   Hence, the truncated domes at bottoms of curb ramps and at edges of train station platforms, etc.  

It seems to me that a 3/4" stone isn't much different in shape and size of a truncated dome...and a blind person may have trouble sensing the difference.  

I wouldn't risk it.  

 
 
LandArch206 (Specifier/Regulator)
27 Aug 09 12:13
"Gravel" as an ADA pathway surface is not preferred, for all of the reasons noted above. 3/4" minus is also too large an aggregate size to start with. That being said, crushed rock--there is a distinction between the two materials--specified at 3/8" minus, with added fines, laid down in 2-3" lifts and well compacted, can be just fine for casual pedestrian use and should be ADA compliant. Decomposed granite is a great material to use, if well maintained. But also consider your transitions onto and off of this surface, and the ongoing maintenance. It's got to be taken care of and raked and compacted on a regular basis to remove any ruts or soft spots that develop seasonally. The "hassle" is why so many folks just opt for asphalt.

BigH (Geotechnical)
30 Aug 09 1:18
Why not add a little cement/fly ash(say 1%) to your 9mm crushed stone - will prevent the stone movements that can occur - or top with a fine seal coat - as one would on the top surface of a triple seal coat (see ORN 31).

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