Broken Arrow City Council
Meeting of: 01-19-2016
To: Mayor and City Council
From: Office of the City Attorney
Title:
title
Presentation, consideration, and discussion on the Hillside Park Retaining Wall (Tiger Hill - southwest corner of Kenosha Street and Lynn Lane), including recommendations on repairs, remediation or possible replacement of the wall, and possible action including direction to pursue a particular design of wall remediation
End
Background:
Following the partial collapse of the Flight Safety retaining wall on the east side of Tiger Hill, Department of Engineering and Construction Staff recommended evaluation of the City's retaining wall. The Acting City Manager approved a contract with Olsson Associates, Inc., a Kansas Architectural and Engineering firm that specializes in segmental block retaining walls, to conduct a geotechnical investigation of the wall.
The report provided general recommendations for remedial action to prevent failure of the wall, but did not explore in detail all possible courses of action. As Olsson's report was very comprehensive and unquestionably laid the foundation for engineering design solutions, their firm was the logical choice to design remediation, repair, or replacement of the wall. On November 19, 2015, the City Council approved a Professional Services Contract with Olsson.
On December 18, 2015, Engineering Staff received the repair recommendations for the retaining wall. Importantly, this correspondence stated that the existing wall design does not meet the several minimum standards of the National Concrete Masonry Association. Specifically, the design and construction deficiencies identified included the following:
• The blocks do not provide enough resistance to resist internal sliding, pullout and facing stability failures.
• At the taller sections, the tensile capacity of the geogrid does not provide an adequate factor of safety against breakage.
• The global analysis indicates that there is an inherent risk for an internal compound stability failure.
The Olsson correspondence, which was sealed by two Professional Engineers, contained five (5) options and is attached for the Council’s review. The Options include the following:
1. Repairing the wall with tiebacks and shotcrete facing. This option would involve leaving the existing wall in place and installing tiebacks or soil nail anchors at regular intervals across the face. The tiebacks would be connected to a permanent reinforced shorecrete facing. This option is the most expensive and is estimated to cost $6,100,000.00
2. Reconstruct the wall. This option would involve complete removal and replacement of the existing wall. Some blocks could possibly be used, but the existing material behind the wall would be replaced with a granular backfill. The estimated cost of this option is $3,300,000.00.
3. Construct a wall in front of the existing wall. This option would provide for a wall to be located between seven (7) and twenty (20) feet in front of the face of the wall and is estimated to be approximately half the height of the existing wall. This option is the most palatable to City Staff, despite the fact that it will absorb additional real estate available for retail and commercial development. The estimated cost of this option is $1,100,000.00.
4. Construct a slope in front of the existing wall. Of the four (4) options presented thus far, this one is by far the most economical and is estimated to cost $300,000.00. It is not recommended by Staff, however, due to the fact that it could take up to 65 feet of developable land.
5. Leave the wall in place and monitor it. This is not recommended either by Olsson Engineers or City Staff.
Olsson representatives will be present at the City Council meeting on January 19, 2016, to discuss the findings contained in their reports and to fully discuss the options identified above. At that time, Staff is asking the Council to consider which option is most palatable under the circumstances so that Olsson can move forward with full engineering design. Importantly, however, there has been some damage to the concrete flume on top of the wall. The flume is a concrete ditch, similar to a sidewalk, designed to transfer water along the top of the wall to an inlet. The water then drains from the inlet instead of seeping behind the wall. The damaged flume has rotated so it is no longer level and is cracked in several places. This damage has allowed water to seep behind the wall and cause additional erosion. Olsson's estimates do not include this cost and will need to be factored into the design and final construction.
On October 1, 2015, the City Manager approved a contract with Stephen Metcalf of McDonald, McCann, Metcalf, Carwile. Mr. Metcalf is an attorney very experienced in the field of construction law. He has been kept abreast of all developments in the evaluation of the wall, as well as recommendations for remediation. Legal Department representatives have met with him on several occasions and have provided him with extensive documentation from the Department of Engineering and Construction.
Mr. Metcalf has prepared letters to the contractor, subcontractor and design engineer putting them on notice of the problems of the wall. These letters will be sent in advance of the City Council meeting.
Cost: As set forth in the attached report
Prepared By: Beth Anne Wilkening, City Attorney
Reviewed By: Finance Department
Department of Engineering and Construction
Development Services Department
Acting Assistant City Manager
Approved By: Michael L. Spurgeon, City Manager
Attachments: Professional Services Contract with Olsson Associations, Inc.
Report of Olsson
Recommendation:
Provide direction on the design for repair of the wall