Interesting article by Steve Sandfort suggesting that trees do dot cause sidewalk damage. The combination of poor sidewalk construction, certain soil types and tree roots may result in damage. he suggests that long term the most cost effective and tree friendly solution is proper and soil specific sidewal design and construction. No mention of innovative soil mixes (e.g. Cornell, Holland). No specifics on soil types and no references cited.

Reply to post by Scott, on March 04, 1999 at 08:08:18:

Yeah, that whole deal bothers me! I would have liked to seen a few references, or at least some substantiation of the adamant claims made there.

What engineering issues are at stake? It seems to me that a tree root is going to go where there is an environment in which it can not just survive, but gain something by being there. If the resources in that area can sustain prolonged scavenging by a root, it will surely grow in girth. I suppose if the sidewalk is tough enough, it could force soil compression below the root as opposed to the sidewalk being the weak point and being forced upward.

I've got to admit I haven't had opportunity to read up much on how to advise an engineer regarding sidewalk construction. Anybody have any comprehensive summaries/articles which cover most everything a person needs to know about what is known? It seems to me that the Trees & Buildings pub would have some dope on the subject, any others?

Just blathering, but sometimes it helps to get a thing or two out there for mutual, think tank, digestion, rumination, fodder for innovation, entrapenureal boldness.

Chew on that Wulky!

Best regards to all,
Happy Spring,
KWK

Reply to post by Kerry, on March 04, 1999 at 08:08:18:

Check out article and refernces in Grabosky and Bassuk, 1996, JofArb 22(6).

Reply to post by Jerry Bond, on March 09, 1999 at 02:09:02:

Well Jerry, you and Nina (Bassuck) and Jason (Grabosky) et al have attracted a sell out crowd in Westchester next week. Yesterday was pre-registration deadline and they had already oversubscribed!

One of the questions I'm still unclear on was also posed here - I think - maybe you can answer or explore it with NB & JB. I understand that the 'Cornell' mix includes a non-compressable matrix of angular stone to structurally support the pavement surface and a hospitable 'soil - moisture retention stuff' mix in the spaces to allow root growth. SO, if the root is happy and it increases in volume does it A) push against the non-compressable matrix or B) develop a different root morphology (non-cylindrical), spreading amorphously between and around the angular stones? If A, where does the energy go? If B, is this a permanent process or at some point will it revert to A; how many years until this question can be answered based on field performance?

Reply to post by Scott, on March 17, 1999 at 12:28:35:

Andy Hillman, Ithaca City Forester in a talk in Bismarck a month or so ago, gave me the impression that it was option B, with growth occurring at a greater depth due to improved aeration. This spreads any force developed over a much wider area by the time it reaches the surface, putting less force on any one spot. With the previous mixes being 95% solids, any growth was generally restricted to airspaces where the surface, through heaving or other phenomena, was lifted to create an airspace between the unlike materials. This would put all the growth force directly above the root on the underside of the paving.
The roots initially grow over and around the rocks, incorporating them, much as the do the wire from wire baskets or other obstacles that may try to restrict one portion of a root during growth.

The local engineer that I gave copies of the handouts to, asked the same questions as Scott.
Did I get any of that right Andy?
Bob U.

Reply to post by Bob Underwood, on March 18, 1999 at 06:45:34:

Good question, Scott, I have been asking Jason Grabosky that since 1994! Andy Hillman's comments represent the Cornell group's best guess, I think, since I don't think there really is any long-term data available yet.
Reportedly, buttress roots usually taper down quickly on many species to "rope-like" thickness. If this is true, then it seems to me that if the Cornell mix can be used far enough away from the mechanical thickening of the buttress roots it has a chance of working well. But until we get good long-term data from excavations, these are just guesses.
Scott, I look forward to meeting you this coming week!

Reply to post by Scott, on March 17, 1999 at 12:28:35:

There are 2 subjects here. One is "How does one make root channels for an immature tree to pass beneath a sidewalk?", and the other is "How does one repair or replace a walk broken by tree roots without cutting roots, breaking the budget, or offending ADA?

We have directed our attention to the latter problem first. We have developed a set of specifications for reinforcing sidewalks and bridging the offending roots without cutting them.

We are using 6" of concrete, 4 runs of rebar, and doweling the new slab to the nearest undamaged remaining slab. This usually requires 15-20 feet of reinforced sidewalk.
After contractors catch on to the idea, it becomes easier to modify techniques to fit situations.

If anyone would like a copy of these specs, please email me your address. We don't have them on our website yet.

Marmon Thompson

Reply to post by Jerry Bond, on March 18, 1999 at 10:29:07:

I couldn't get in! Maybe you can talk Stepanie into letting me sneak in the back door. Or handle your overheads or hide in a corner.

I will try to stop by, I need to catch up with Chris Luley and Dave Bloniarz as well.