Monday, January 28, 2008

Concrete versus Limestone

posted by Elizabeth Fama


You've got to hand it to the SAVE THE POINT group: they had a brilliant marketing campaign. Look at this (horrifically misleading) ad they put in the Hyde Park Herald in April of 2003, when they knew full well that the stretch of all-concrete revetment between 51st Street and 54th Street was no longer what the City was offering us:


Apparently, all's fair in love and marketing.


Implicit in this visual message is not only a critique of design, but also of material. The concrete is photographed to look cold and sterile (at the sight line of a rat), and the limestone is photographed from above, with warm human beings delighting in their surroundings.

In typical bureaucratic fashion, it took the City too long to come up with its own visual campaign of what it was really offering:



Some of our readers have commented that they do prefer the look of limestone, and they have wondered all along why the City can't just re-build Promontory Point out of limestone. After all, the limestone blocks from the 1930s are fully intact, while some of the cement sidewalks the City poured just last year in Hyde Park aren't.

I'm not a structural engineer, but I'll tell you what I know about concrete versus limestone.

1) Yes, individual limestone blocks are hard and durable. But the Army Corps of Engineers will not build a revetment for us that does not have a steel and concrete core. Why? Because limestone blocks can't be anchored against wave action and the shifts and separations that freezing and thawing cause.

2) If good-quality concrete is poured in the right way and at the right temperature and humidity, it's durable -- very durable. The contractual requirement for the lakeshore project is that the concrete must resist 5,000 lbs of pressure per square inch. As the contractors pour the concrete, they pour sample cylinders on site for the Army Corps to test after the concrete has cured.

3) The Army Corps and the City are willing to re-use all of the existing limestone, by (a) making the top two steps of the revetment out of limestone blocks, (b) building limestone steps into the water for swim access, and (c) covering the steel pilings with a tumbled limestone toe berm. These non-structural uses of limestone will at least allow us to retain some of the beauty of the stones, to sit on them, and to wade on them. The Illinois Historic Preservation Agency has said that this mixed-material design satisfies its requirements for historic preservation. The famous Memorandum of Agreement (a document that I'll recap in a future post) does not specify building materials, nor does Barack Obama's "Scope of Work" document.

Here's a series of photos that I find revealing about the strengths and weaknesses of limestone:

In the foreground of this shot you can see how the wood pilings and steel rails have failed, and the limestone blocks have shifted and fallen. (The old sub-structure is a "crib" or cage of wood pilings, steel rails, and tie-rods, which is filled with "stone aggregate," or coarse, crushed stone.) In the background of this photo you can see the "concrete coffins" at the tip of the Point -- a concrete repair of the promenade that took place around 30 years after the Point was built and is now itself around 45 years old. The concrete coffins are still very much intact.


Thus, concrete as a material is sturdy enough to handle 45 years of crashing northeast waves, and 45 winters of freezing and thawing. But that's only part of the story. Since the sub-structure at the tip of the Point was never repaired, the wave action is still eroding the stone aggregate underneath the concrete promenade, and causing the limestone steps behind the coffins to buckle:

The stone aggregate must be almost gone under this section. But even beyond that, the erosion of the waves is sucking dirt and sand from under the grassy meadow-side of the revetment as well:


When the Point was built, the soil level reached the top of the top step of the revetment. Now my friend Gerald can stand 3 - 4 feet deep in the ditch behind the top step.

And just look at these caves:

(My kids are not allowed to walk above this section.)


The new revetment won't have a "crib" by the old definition. The contractor will drive strong, stable steel piling, and then backfill with crushed stone before pouring the concrete promenade. The concrete is reinforced with rust-resistant rebar (rust would cause the rebar to expand, which would crack the concrete around it). The steel piling does most of the structural work, and the concrete core protects the backfill from erosion because it doesn't allow water to penetrate.


In the end, the longevity of the core of the new revetment will depend on sound engineering and quality control of inputs and labor, not on whether it's built of limestone, or concrete, or kryptonite.

9 comments:

Famac said...

Even though they used the ugliest picture possible, the concrete still looks better.

chicago pop said...

I wonder if, when the Point finally erodes into the lake, the Save the Co-Op people will organize a New Orleans jazz festival to mark its disappearance?

That's an amazing piece of political marketing you've put up there, Elizabeth, thanks for digging that up. Karl Rove would be proud of that little poster, maybe even Lee Atwater of "Willie Horton" fame. Who knew our own Hyde Park activists were just as adept at the black arts of political advertising?

EdJ said...

I know you wrote it before, but what's the status of the funding for the final study and has it been allocated for spending.It seems like this should just be a checklist study of compliance with regulations (concrete foundations, Americans with Disabilities access, etc.) preservation standards (top two steps in limestone, etc), safety regulations, long term durability and maintenance, etc.

I've seen the broen concrete and twisted metal just north of the point. Is there any potential that the city could just fence off the Point because of the threat to personal safety? Is there a liability issue here for the city if someone gets hurt due to the deterioration of the structure?

Famac said...

There must be because they removed the lifeguards a few years ago, and handed out a few tickets last year (if memory serves).

Elizabeth Fama said...

EDJ, I think you've hit the nail on the head with these two questions. They get to the absolute heart of the Point issue:

1) There is no action at the Point, or at least the action that is happening is going at the glacial pace of legislation. We're talking years here, if we're going to wait for Obama's committee to recommend a new plan. And what happens then? Will the SAVE THE POINT group fight it further, with lawsuits based on Jackson's undefined "preservation" legislation? Stalling is exactly what the SAVE THE POINT folks wanted. They count it as a success, but it represents an enormous failure because...

2) There is a real possibility that the Point could get shut down if one bad incident occurs in the next few years. Those photos I showed of the tip of the Point have caves that could honestly kill a child. The north side of the Point was not staffed with a guard this past summer -- the Point would not only be shut down if someone drowned, but the sanctioned deep-water swimming access of the Compromise Plan could be revoked. It's a gnarly, treacherous entry into the water on the north side, throngs of people continue to swim there, and an injury is just waiting to happen.

My gut feeling is that the City would be just as happy to punish us by shutting down the Point, leaving it inaccessible for as long as it wants, and then sweeping in and doing whatever design it chooses because it's "urgent."

Honestly, dear readers, you are not nearly worked up enough about the Point.

Send me an e-mail and I'll mail you a free FIX THE POINT bumper sticker. Please!

fama.elizabeth@gmail.com

SR said...

As far as funding for Obama’s committee, so far as I know the latest is this, from a Nov. 14th 2007 Hyde Park Herald article, headlined “In October Congress passed, and in November overrode President Bush's veto of the Water Resources House and Senate Conference authorization act. Next is to get actual funding.” The article states,
”the bill authorizes fund for a third-party study that must adhere to national preservatin standards in its review of plans for the beloved lakefront park,” and later, “Lamb said the funds would likely be appropriated next year.”

I don’t really understand how this stuff works, so I guess it would come up in the budget for the next fiscal year that they pass in Congress? Which I guess would be 2009 since 2008 is set already, as far as I know.

You can read the Scope of Work document for the committee here.

As for how bad the Point can really get, I came across an interesting quote from Daley about the Point, purportedly an unscripted outburst at a breakfast meeting with some Northside activists who were also protesting what was being done with their own strip of lakefront: “As to those people in Hyde Park, they're not getting anything. Promontory Point can sink into the lake, and God help them if it does.” This was from sometime in 2003.

It has always seemed to me that it is when Daley is at his most exasperated that you know the King Has Spoken. I think on some level nothing's happening (or happening very, very slowly) because the City has basically lost interest in the project, and total collapse of our revetment is not really an unacceptable outcome for Daley. If it happens, he can probably just go ahead and do whatever he wants on an "emergency" basis, with many fewer headaches than would come with having to go through any more rigamarole with the "community." I think it may well be the case that a serious injury will be the trigger for that, if it happens.

Part of what's weird for me about figuring exactly how to talk about what's going on with the Point (for the purpose of writing some stuff for this alleged website), is that it's not clear that the City really wants to do anything at this point, and the STP people have always been more about fending off the City and don't really think anything needs to be done at all. So in a sense there are currently NO sides "fighting" about anything, and maybe this committee is more or less what both "sides" want, a kind of officially-good-sounding but ultimately pointless and glacially slow process that puts off the need for any decisions or questions about anything, hopefully for years and years.

On the other hand, I really do think that sooner or later, somebody's kid is going to crawl into one of those gaping holes and not come out again, so there is a need to find some kind of lever to push to make something happen.

chicago pop said...

Send me an e-mail and I'll mail you a free FIX THE POINT bumper sticker. Please!

OK, ok, I've had mine for a week or so now but have been too lazy to put them on my car. Will do it this afternoon. Then if any Point Savers see it they'll probably have a Jack-Attack.

Elizabeth Fama said...

SR said, "On the other hand, I really do think that sooner or later, somebody's kid is going to crawl into one of those gaping holes and not come out again, so there is a need to find some kind of lever to push to make something happen."

That's the question I want our readers to think about: What can we do to get the process of fixing the Point underway? Is it possible to petition Hairston to override all this rigamarole and say the Point is becoming dangerous, then sign off on the Compromise Plan and get work started? We know Toni Preckwinkle would be gutsy enough to do that if she set her mind to it, but has Hairston ever been that decided? It's almost like it's "convenient" for everyone involved to let nothing happen. Meanwhile, Hyde Parkers think vaguely that something is happening -- something legislative that's out of our hands -- and leave it at that.

I do wonder if the shouting activist method would shake people up here. Like holding a rally at the Point and inviting the TV news? It's not my style, but the shaking needs to happen.

SR said...

I dunno, I think since this process that has the imprimature of no less a personage than Barack Obama is underway, however slowly, we would just look like crazy people if we starting protesting in favor of short-circuiting it. The futility of this committee isn't really obvious unless you read all the history of this and realize how entrenched and intransigent the mutually-contradictory goals of the City and Save the Point truly are.

I wonder if we could at least deal with the safety issue? I don't think we can do anything in a stopgap way to make swimming safer (and given the stencilled "no swimming" signs, the tendency of the City to ticket sometimes, and the obviously gnarly appearance of the "access" points, Point swimmers are at least duly warned), but maybe some of those great big holes in the steps and promenade could be filled in, good enough to last maybe 3-5 years? I think it should be pretty obvious to everybody whether this committee is really going to accomplish anything or not by the end of that timeframe.

I don't know what it would involve, exactly; the last time I walked on the promenade (summer before last, IIRC), I thought I could hear water rushing down in some of the holes, so you might need to dump some gravel or some kind of fill in some of them, and handfit some rocks in the bigger gaps before mortaring.

The danger of agitating for something like that would be that conceivably the City would use "citizen complaints" about safety as an excuse for an "emergency" rebuild, which might end up looking like 51st St, and nobody wants that. At the same time, the Save the Point people might view any work proposed to be done out there as a cover for the City doing something like that, whether the City is really planning anything or not.

We might be able to forstall some of that if we had a better idea of what it would involve (ideally no heavy equipment and a pretty small amount of money; if I were hiring someone to do something like on a rock wall that big on my own property, I'd be expecting something around $10 K, probably). Maybe we could have a contractor look it over for us and give us a very specific proposal, and we could propose that with all the details and specs and cost estimates to Hairston?