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Grout Expectations: The Central Subway Plan Tries to Compensate for its Shortcomings, but May Just Frack it Up 

Wednesday, Apr 17 2013
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In the days before cell phones, bored undergraduates in the restrooms of institutions of higher learning passed time by scrawling puns in the grouting between wall tiles: "The Grout Gatsby;" "It's the Grout Pumpkin, Charlie Brown;" "Grout Expectations;" and, of course, "Three Strikes and You're Grout."

This, incidentally, is called "groutfiti," and could be the first, last, and only time many people gave a moment's thought to grout. North Beach residents, however, may be thinking a grout deal about the stuff in the coming weeks. As part of the ongoing plan to extract Central Subway tunnel-boring machines from the derelict Pagoda Palace theater, an engineering firm contracted by the city has proposed injecting "compaction grouting" into the earth to prevent nearby century-old, brick-foundation structures from sinking during the subterranean construction project.

An engineer retained by opponents of the Central Subway project has sworn that shooting grouting beneath the streets of North Beach in hopes of preventing settlement is doomed to failure — as either a preventive or reactive measure. And independent engineers say that administering compaction grouting is a complex and delicate procedure not to be undertaken lightly; if the mixture of cement, sand, and water is injected into the earth at too great a pressure, North Beach could experience an impromptu fracking.

In a part of town where you can't even open a chain store, it's a solid bet that no one would go for that.

For years, Douglas Ahlers hoped to transform the Pagoda Palace back into a thriving theater. That never happened. Doing so would have required rivers of money rivaling the actual river Ahlers suspects flows beneath the Palace.

His hopes to build a basement for scenery storage and a prop shop were quashed when "the report from some test borings showed that there were some issues with water — likely an underground stream coming off Russian Hill," he writes in a recent e-mail. Excavating the site "was put to me as something well outside of the budget."

Ahlers, however, didn't possess the resources of the city, its Municipal Transportation Agency, and the federal government, all of which are intent on pushing through the Central Subway, the Tropicana of politically juiced projects. Over the past decade, its price tag has leaped by 150 percent while the line's estimated ridership has fallen by 65 percent. In order to stave off the debacle of extracting tunnel-boring machines from the middle of Columbus Avenue, the city has proposed the two-for-one deal of doing away with the eyesore that is the Pagoda Palace while unearthing the machines out of the public right-of-way. Last week, new construction estimates pushed the anticipated price of the endeavor from $9.15 million to $13.7 million. The cost was pegged at $8 million in February and was sold as adding only $3 million to project costs as recently as December. Whatever the final total, the money will be siphoned from Muni's general reserve.

A proposal presented to the city on March 1 by the engineering firm Arup lays out what this undertaking would entail. The proposal is candid that much of the analysis remains to be done. "The effects of the shaft and [boring machine] excavation on the existing building and utilities" are notably undetermined. A January Arup memorandum included a map of 10 "buildings in the influence zone of the Retrieval Shaft Works."

In the event these or other structures are affected, "For the purposes of our scope and fee, it has been assumed that compensation grouting will be the preferred solution to control settlements," notes the proposal.

"I can't tell you how idiotic this is," growls Lawrence Karp, the veteran engineer hired by Central Subway foes: Injecting grout beneath aging structures will neither prevent those structures from settling nor prop them back up if they do. "That technique will not work in this type of soil situation," he says. Karp describes the earth beneath North Beach as "dirty sand. Fill. Essentially garbage" strewn there following the 1906 earthquake. Compensation grouting would work with uniform sand — "but, here, it's just gonna run all over the place."

Luis Piek, the Arup engineer who prepared the proposal for the city, was taken aback that it had been obtained by SF Weekly. He declined to discuss project specifics but did "stand behind our ability to deliver what's in the report." Independent experts, however, say that the grouting process Piek described in the proposal as "the preferred solution" would be a complex and costly affair.

"It's a very involved process," says tunneling engineer Gregg Korbin. "It's expensive and it takes talented people." Douglas Hamilton, the engineering geologist for the Devil's Slide project, concurs: "Grouting is a mysterious process." If grout is injected at too low a pressure, he continues, it won't settle in the right place. And if it's applied with too much pressure, you'll create fissures — and that's fracking.

Deep beneath the earth's surface, fracking can cause earthquakes. Hamilton says this won't happen at shallow depths in North Beach — "but you could end up with basements full of grout."

Definitive soil samples revealing fine sand or "garbage" would go a long way toward calming fears or lending validity to Karp's gloomy scenario. Oddly, at this point in the game, one doesn't exist. The sole sample gathered on the Pagoda Palace site was a 31-foot boring made in 2008 in anticipation of a taqueria and condos being constructed above. The proposed retrieval shaft for the boring machines — a somewhat more involved project than a taqueria — would go down 42 feet. In the world of engineering, where sayings like "measure twice, cut once" are commonplace, it comes off as strange to devise a plan and then obtain a soil sample.

"I would think it prudent to have at least one very well-sampled boring that went at least to that depth [42 feet] and maybe 10 or 20 feet below the maximum intended depth," Hamilton says. "You don't know what you're dealing with without information like that."

Muni spokesman Paul Rose noted that more borings for soil samples — which, hopefully, will go as deep or deeper than 42 feet — will be undertaken prior to construction, slated for next month. If need be, Rose adds, "the retrieval shaft will be amended as necessary to address those conditions."

Because the last thing anyone wants is non-consensual fracking.

About The Author

Joe Eskenazi

Joe Eskenazi

Bio:
Joe Eskenazi was born in San Francisco, raised in the Bay Area, and attended U.C. Berkeley. He never left. "Your humble narrator" is a staff writer and columnist for SF Weekly, which he has written for since 2007. He resides in the Excelsior with his wife, 4.3 miles from his birthplace and 5,474 from hers... more

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