February 20, 2012

Ledcor is repairing overpass in Kelowna

RICHARD GILBERT

staff writer

Ledcor is undertaking repairs to the retaining walls at the Westside Road Interchange in Kelowna, B.C., after structural engineers carried out an assessment to find out why a section of concrete facing collapsed last year.

“This has been an unusual event, but it is important we move forward at this time,” said Murray Tekana, district manager with the B.C. Ministry of Transportation.

“We are confident the new facing system will work, while we wait for the final analysis of the collapse to be completed.”

A section of concrete facing wall on the west abutment retaining wall at the Westside Road Interchange gave way on Nov. 20, spilling dirt fill onto one of the southbound lanes of Highway 97 underneath the overpass.

Structural engineers from Urban Systems, the owner’s engineer assessed the wall area and overall structure to determine an appropriate course of action.

The Ministry of Transportation also engaged a bridge engineer, Buckland and Taylor Ltd., to investigate the cause of the collapse. "The repair work is based on the assessment, which found there was a failure in a component in the wall facing system" said Tekana.

"The one factor that is clear is the failure of this component, which contributed to the collapse. But, there are other factors that are still being assessed." Buckland and Taylor has done detailed testing on building materials from the construction site.

These tests have determined that a contributing factor in the collapse of the retaining wall was embrittlement at the bends in certain steel reinforcement bars connecting the concrete facing panels.

"For Ledcor to proceed with the repair, they have developed a new facing system in partnership with SSL,” said Tekana.

"The new facing system uses a different approach to the connections."

Ledcor has mobilized a team of engineers to assess the collapse, which includes engineers from SSL, the supplier of the retaining wall.

According to Tekana, the wall repair is being undertaken in two phases.

"The first phase was to stabilize the fill behind the facing panels using a shotcrete application,” he said.

The new facing system will be connected to the shotcrete and have new connections to the wall in front. The space will then be filled with concrete."

The first phase involved the removal of all the panels under the abutments on east and west facing walls, the preparation of the soil and the application of shotcrete on the exposed face of the soil to prevent weathering.

It was also necessary to prepare a new mounting surface for the finishing panels.

The retrofitting of the panels is a complex process, so it took more time than anticipated to design a repair that ensures quality and durability.

The investigation into the failure of the retaining wall is taking place during repairs The investigation includes detailed geotechnical analysis, further materials testing, analysis of soil settlement and mapping of the failure areas.

It will also include an analysis of findings from taking apart the opposite wall to learn about other factors that may have contributed to the collapse.

Ledcor anticipates repairs will be complete by mid-March.

Construction of the Westside Road Interchange began in 2009 and the overpass opened to traffic on October 29, 2011.

The overall value of the project is $41.8 million.

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