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Replacing a Problematic Retaining Wall

Ron Kujawa is CCLP, and Chairman of the Board for Kujawa Enterprises, Inc. (KEI) located in Cudahy, Wis.

The Riversite is a prestigious mixed use development on the Milwaukee River located in Mequon, Wis., an upscale suburb north of Milwaukee.

When Ed Potokar and his partners from Riversite Associates, LLC purchased the property as a real estate investment, they had only an inkling that there was a serious problem with a timber retaining wall on the south end of the property, in close proximity to the property line. The wall was over 200 feet long, and between 12 and 13 feet high along the property line. It curved back on the east towards a building, and on the west into a parking lot, which was used by tenants and customers of a restaurant located nearest the wall.

After consulting with an engineer who had been involved in the original construction of the building and the wall, the sellers and buyers agreed to a slight reduction in the price. This was based upon his estimate of future repairs to the wall. As it turned out later, actual cost estimates were exceeded by more than 10 times.

As time passed, the deterioration of the wall accelerated. It was not only causing severe damage to the parking lot, it was seriously threatening a disruption of underground utilities. It even posed possible jeopardy to the building itself.

How Bad Was It?

Guided by an on-site engineer, a width of 11 feet was excavated running the length of the wall. This was backfilled with number one clear stone. Upon that base the initial four courses of a Keystone wall system was installed.

The consulting engineers, while they couldn't agree on a solution, did agree that the original design was inadequate. According to one report, " . . . The design intent clearly was to have some of the timbers erected perpendicular to the face of the wall and to have these timbers act as 'deadmen.' The ends of these timbers were 'anchored' into the backfill with

re-inforcing rods driven through the ends. The problems with this anchoring system are two-fold" (1) The deadman timber is not long enough to extend beyond the active pressure in the backfill, and (2) the reinforcing rod is inadequate to properly anchor the timber. It will simply bend when stressed. Essentially, what happened at the failure area is that the wall deadman and rebar system was all in the backfill zone that moved and failed." Another report went on to say "The wall was not built in accordance with the requirements of the design of the drawings you provided, although in my opinion, that design was flawed and would not have worked anyway."

All of the base work is under the finished grade at the base of the wall, and approximately 6 1/2 feet below the original base of the failed wall. Work had to be performed around an exposed gas line as well as exposed sewer lines.

Solutions offered by the engineering consultants, with no guarantee of success, varied from:

• Using a foundation contractor to design and build a

reinforced concrete retaining wall

• Installing steel soldier pilings and using precast concrete

panels to create a wall

• Regrading the site, sloping the ground to the property lines on the south and west. This would require a much

smaller wall

• Using two walls, one at the setback from the property line and the second much further back

• Build a timber wall using Chance Anchor Systems

None of the above scenarios appealed to the owners for various reasons. The proposed solutions were either in

non-compliance with the local municipality's codes, they "robbed" far too much parking area, or the cost of the proposed solution was too high.

Somewhat frustrated and confused, they sought advice from their property manager, Jody Nelson of MLG, a real estate development and property management firm in the metropolitan Milwaukee area. Nelson suggested that Potokar contact us at KEI. The engineering reports and the solutions offered were at one time confusing, and possibly even conflicting. Couple this with the fact that a Landscape Contractor installed the original wall and according to the original owners, spared no expense, was reason enough for Potokar and his partners to be skeptical. He did though, agree to meet with us.

Solutions

The building of the retaining wall took the combined efforts of the Landscape Contractor, the engineering firm and the modular concrete manufacturer to design a proper wall that all three could collaborate on, agree on, and stand behind.

We examined and analyzed the various reports, and made visual inspections of the wall. After further research and discussion, we felt we had an effective solution. We were able to convince Potokar that a modular concrete retaining wall with geogrid reinforcement would likely be the most technically and economically feasible method of reconstruction. We had to convince him that we had to work with a willing engineering firm and a modular concrete manufacturer to design a proper wall, and to build it exactly according to the specifications that all three of us would collaborate on, agree on, and stand behind. The requirement for an engineering firm to be involved was a requirement of the municipality, but, more importantly, no one wanted a failure this time around.

Prior to writing any specifications, multiple soil borings were required. We were confident that there would be substantial geotechnical remediation with engineered backfill, and possibly an extensive network of sub-surface drainage needed. Just how much and how extensive, however, was far beyond even our wildest expectation.

We knew up front what our engineering costs would be, and we were able to project certain unit costs for construction, but we were naturally reluctant to establish a firm price because of all the unknowns. We proposed a modified time and material arrangement with various expenditure ranges, all clearly defined. Estimates were segregated as they were identified, and reasonable contingencies were added. A tentative schedule was established with provisions to modify if necessary. When all of this was agreed upon in principle, we were ready to proceed.

The project began with location of all underground utilities, and with the selection of various sub-contractors and the suppliers we intended to use. The work began with relocating the restaurant's dumpster pad, including demolition of the existing pad and corral. Next, we had to gain access to the area at the base of the crumbling wall. This necessitated both snow removal as well as considerable brush clearance. The majority of all demolition had to occur from the topside because of space limitations below, so we employed a backhoe with a 28 foot reach.

Wrecked timbers and over 2,000 cubic yards of back fill were removed from the construction site. The excavation and amount of backfill that had to be removed was the largest unexpected expense that was incurred.

In addition to the wrecked timbers, over 2,000 cubic yards of "back fill" had to be removed. We were fortunate to locate a licensed dump site within reasonable proximity that would accept the "quality" of debris that we removed. The excavation and the amount of backfill that had to be removed was the largest unexpected expense incurred. The fill under the parking lot consisted of remnants of a burned down building, construction debris and waste, sand, concrete and asphalt chunks. The "soil" it contained was less than desirable.

Next in order was the excavation of the area where the base of the wall would be located. Guided by an on-site engineer, we dug deep enough to reach suitable virgin clay soil. We further excavated to a depth which permitted a base of three feet of compacted traffic bond. Behind the base, we excavated to a width of 11 feet, running along the entire length of the wall. This was backfilled with number one clear (no fines) stone, compacted in six inch lifts. Upon that base, we installed the initial four courses of Keystone modular concrete wall system, tied back a minimum of 11 feet with Tensar GeoGrid stabilizing fabric, as prescribed by our engineering protocol. All of this base work is under the finished grade at the base of the wall, and approximately 6 1/2 feet below the original base of the failed wall.

Each succeeding course was installed with a geogrid stabilizing fabric tied in every second course. At times, the geogrid fabric extended up to 16 feet. All backfill was compacted with a sheepsfoot compactor in six inch lifts. All work was checked during regular visits from our engineering firm; the municipal inspector and the owner were usually there on a daily basis also.

Great care had to be exercised, as we had to work around an exposed gas line as well as some sewer lines. We did not encounter any free water during our soil borings (which went to depths between 21 and 25 feet), but did install a collector system connected to manholes on the surface, and vacated the water via a 12 inch pipe that emptied into a drainage ditch filled with rip-rap. The water eventually moved into the adjacent river.

Before the final backfilling was completed, the electrical and lighting contractors were scheduled, and their work completed. Posts for the guard rail were set, and finally, the caps were set and backfill brought up to subgrade prior to the installation of new asphalt.

The Final Product

The finished wall located in Mequon, Wis. was constructed with engineered backfill and ranges in height from zero to 14 feet. Construction began in the late winter and was completed in the wettest May in Wisconsin history.

Two hundred and twenty feet of crumbling, bulging timber wall, plus more than 2,000 cubic yards of unsuitable backfill and debris were replaced with a Keystone modular concrete wall installed with engineered backfill. The wall ranges in height from zero to 14 feet. This project began late in the winter and was completed during the wettest May in our history. Special care was exercised to create a minimum of disruption, which pleased the tenants, and the project came in under the cost estimates, which certainly pleased the clients.


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June 18, 2019, 6:46 pm PDT

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