Feats of Engineering ? Retaining wall at St ... - Finance & Commerce

Posted: 11:24 am Tue, February 28, 2012
By American Council of Engineering Companies of Minnesota?
Tags: Encompass Inc., Howard Noziska, Jerry Theis, Kent Jones, St. Paul?s Episcopal Church, Theis Construction

At St. Paul?s Episcopal Church, overlooking Lake of the Isles in Minneapolis, rebar and stainless steel ties designed by Encompass Inc. were installed in a difficult retaining wall project. (Submitted photos)

Location: 1917 Logan Ave. S., Minneapolis

Firm: Encompass Inc., Eden Prairie

Completion date: November 2011

Project team: Howard Noziska, Kent Jones, Encompass Inc.; Jerry Theis, Theis Construction

Editor?s note: The Feats of Engineering feature, which runs occasionally in Finance & Commerce, features projects completed by members of the American Council of Engineering Companies of Minnesota. The content comes from ACEC and the firms.

Aging, structurally unsound retaining walls are a relatively common problem in Minneapolis. The leaning wall behind St. Paul?s Episcopal Church, holding back the prominent hill overlooking Lake of the Isles on which the landmark church was built, posed extraordinary problems ? ?a challenge of almost biblical proportions,? said Howard Noziska, president of Encompass Inc., the Eden Prairie-based engineering and forensic analysis firm retained to find a solution.

Noziska describes the steepness of St. Paul?s site as ?scary.? But the steepness was only part of the challenge in fixing the collapsing wall and stabilizing the hill. Compounding the problem was an extremely restricted location that not only offered physical barriers ? stairs blocking access to the wall ? but religious and cultural barriers as well, in the form of the buried cremains of deceased members of the congregation and the integrity of a historic structure that had to be assured.

Conditions were exacerbated by the fact that small trees planted many years ago were now fully grown, with their roots a major part of the problem, and several seasons of record snowfalls and heavy rain had loaded the soil with moisture. Taken together, all of these conditions were increasing both the vertical and lateral loads on the retaining wall itself ? a structure a foot thick, 6 feet high and nearly 60 feet long.

?The hill was doing what comes naturally,? said Noziska, ?sliding, moving downhill, and putting great pressure on the old retaining wall and related sidewalks and stairways. Uncorrected, it presented a potential danger to churchgoers as well as a threat to the church structure itself.?

Eden Prairie-based Encompass Inc. designed and supervised the installation by Theis Construction of a series of ?helical piers? ? large screw-like rods, twisted into the soil to provide the counterbalancing forces the retaining wall needed to restrain and stabilize the soil behind the wall.

Any solution had to be affordable for a congregation with limited resources, yet one that would endure for decades. Encompass? answer was a creative combination of advanced engineering thinking and old-fashioned common sense.

The firm designed and supervised the installation by Theis Construction of a series of ?helical piers? ? large screw-like rods, twisted into the soil to provide the counterbalancing forces the retaining wall needed to restrain and stabilize the soil behind the wall. This created counterforces to the hillside?s natural inclination to keep sliding and pressuring the wall itself.

A new foot-thick reinforced concrete wall with new buttresses was strengthened by the installation of extensive rebar reinforcing rods.

Because of the accessibility problem, all of the concrete required for construction had to be ?bucketed? up the hillside. To reach the difficult work area, temporary bridges were built across the steep stairways, sufficient to provide access to the work area by Bobcat without blocking entry to the church for services.

The result? ?A strong new retaining wall that will serve the congregation and protect St. Paul?s historic structure for decades into the future,? Noziska said.

To submit projects for consideration in Feats of Engineering, please email the following information to David Oxley, ACEC/MN executive director, at doxley@acecmn.org: firm name, project name, location and description; projected or actual completion date; firm project team and overall project team; additional details of interest to the architecture, engineering and design community; phone number and email address for a project. High-resolution renderings or photographs (minimum of 1MB) also should be submitted. For more information, call 952-593-5533.

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Source: http://finance-commerce.com/2012/02/feats-of-engineering-retaining-wall-at-st-paul%E2%80%99s-episcopal-church/

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