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Agenda Item - 2021-12-21 - Number 5.3 - Resolution 21-41, North Shore Road Bridge Retaining Wall Repair 5.3 COUNCIL REPORT ___ o QREGoNI' Subject: Resolution 21-41, Design Update for WO 324— North Shore Road Bridge Retaining Wall Repair Meeting Date: 12/21/2021 Staff Member: Stefan Broadus, P.E. Assistant City Engineer Department: Public Works/Engineering Action Required Advisory Board/Commission Recommendation ❑ Motion ❑ Approval ❑ Public Hearing ❑ Denial ❑ Ordinance ❑ None Forwarded ❑X Resolution ❑ Not Applicable ❑ Information Only Comments: ❑ Council Direction ❑ Consent Agenda Staff Recommendation: Replace the northeast and northwest retaining walls of the North Shore Road Bridge approach with Lock+Load MSE walls, or similar. This is an economic solution that should provide structural stability and complement the existing retaining walls on the south side of the bridge. Authorize the City Manager to amend the public improvement contracts with DOWL and Emery & Sons to construct the designed walls. Reopen Northshore Road to vehicular traffic upon completion. Recommended Language for Motion: Move to adopt Resolution 21-41. Project/ Issue Relates To: Issue before Council (Highlight Policy Question): ❑X Council Goals/Priorities ❑Adopted Master Plan(s) ❑Not Applicable 503.635.0215 380 A Avenue PO BOX 369 Lake Oswego, OR 97034 www.lakeosweao.city Page 2 EXECUTIVE SUMMARY City staff has evaluated the condition of the retaining wall on the northeast approach of the North Shore Road Bridge which was the cause for the closure that has been in place since July of 2021.The geotechnical and structural findings support replacing the retaining walls on the northeast and northwest approach with Mechanically Stabilized Earth (MSE) type walls. BACKGROUND On July 13, 2021, a Notice to Council was sent regarding the North Shore Road Bridge closure. The days before the closure, Lake Corp had notified City staff about concerns with the retaining wall on the northeast approach to the bridge based on their observations. City staff then performed visual inspections with the assistance of Geotechnical and Structural consultants. The wall appears to be moving slightly to the east and rotating about the base. The findings suggested that the concerns were valid enough to close the bridge to vehicular traffic and perform a more comprehensive evaluation. Staff then negotiated and executed contracts with DOWL (Engineering Consultant) and Emery & Sons (Contractor), who have expertise in retaining walls. DISCUSSION Engineering Analysis & Solution The project team considered several alternatives for this retaining wall including leaving it as existing, a localized spot repair, and full replacement. To supplement the visual inspections performed, an area of the roadway was excavated to determine geotechnical properties. Those findings were used when performing the slope stability analysis of the existing wall configuration. The calculations suggest a slope stability factor of safety of approximately 1.1. For reference, a factor of safety of 1.0 represents a structure that will fail exactly when it reaches the design load, and cannot support any additional load. A factor of safety of 1.5 is the required minimum design for a new structure. Since the factor of safety is below 1.5, leaving the wall as existing or performing a spot repair is not appropriate due to the risk to public safety. 503.635.0215 380 A Avenue PO BOX 369 Lake Oswego, OR 97034 www.lakeosweao.citv Page 3 The remaining option is to replace the wall. The height of the required wall prohibits using a similar rockery wall. Instead, an MSE type wall will be required to provide the specified factor of safety. An MSE wall is an industry standard approach to provide vertical walls of this height. The MSE wall will need tieback anchors, which are horizontal elements that extend from the back of the wall to provide additional resistance to wall movement and thus increase the stability. The required length of the tiebacks has been calculated to extend into the northwest approach retaining wall. This requires that both the northeast and northwest retaining walls be replaced together. +� a Of NE Retaining WaII Tieback Anchors NW Retaining Wall 41.110* • Neighborhood Impact and Comments Since the road closure, there has been chatter on social media platforms from citizens regarding the possibility of leaving the bridge closed to vehicular traffic permanently. City staff, including emergency responders, strongly recommends against this as the bridge provides a critical alternate north-south route in the event State Street is blocked due to a crash, a stopped train, or construction. Also, the closure increases the travel time for several trips originating or ending within the neighborhood. Traffic counts were collected before and after the closure was in place. The data suggests that traffic on North Shore Road east of Lake Shore Road reduced by approximately 160 daily trips, or roughly 17 percent, following the closure of the bridge. This could be accounted for by the redirection of traffic from homes along North Shore Road west of Berwick, on Cabana Lane, or on Lake Forest Drive. 503.635.0215 380 A Avenue PO BOX 369 Lake Oswego, OR 97034 www.lakeosweao.city Page 4 PERMITTING It's important to note that construction work in Oswego Lake is regulated by Oregon Department of State Lands (DSL) with coordination from Oregon Department of Fish and Wildlife (ODFW). Rebuilding the northeast and northwest retaining walls are expected to be considered an emergency repair and the permitting timeline would be minimal. The southeast and southwest retaining walls do not show the same signs of early failure as was detected at the northeast retaining wall. This is likely due to the angle and height of the walls resulting in greater stability. If the City were consider replacing the southeast and southwest walls at the same time as the northeast and northwest walls, the work would no longer be considered an emergency repair. Thus, the permitting timeline would likely be closer to 12-18 months from the submittal of the application to the time when construction could begin. ALTERNATIVES Based on the results of the slope stability analysis, taking no action and continuing to monitor the northeast wall is not recommended due to the risk to public safety. Also, based on site constraints, the most viable wall type is an MSE wall. The difference among the alternatives to consider is essentially just the appearance of the wall face. - ---- f .1,1001"V._ ,i?,„,..09-A ---- -— ---• -- _ 1 IN07:i 1;''-:. • ` "1/:?/:e.,41,1 ! 01111,0000r4 , • __, Y_. -^- ' + . .r 1101111111111061 � Imo" �c 1 - - a } " — Ultrablock Wall Reinforced Earth MSE Wall i 44 -- --. _ l` \ 31.• Lock+Load Wall 503.635.0215 380 A Avenue PO BOX 369 Lake Oswego, OR 97034 www.lakeosweao.city Page 5 SCHEDULE In the Notice to Council dated 7/13/2021, the very preliminary timeline suggested 6-8 months to complete a repair and reopen the road to vehicular traffic. After completing the more comprehensive analysis, a more confident schedule is shown below: Task Anticipated Timeline Discovery & Closure July 2021 Design and Construction Contracts Executed September 2021 Geotechnical & Structural Analysis November 2021 Final Design and Construction Pricing January 2022 Construction Starts February 2022 Construction Complete May 2022 While City staff have developed and implemented a communications plan to keep the neighborhood and commuter traffic updated on the project, collaborative workshops to provide input on aesthetic considerations, namely the pattern of the MSE wall, are not planned. If the Council would like staff to coordinate an outreach effort for the aesthetics, that can certainly be performed.That task would push the schedule out about 3 months. Also of note is the impact that the general availability of construction materials, specifically MSE panels, could have on the construction schedule. At the time of procurement, the materials could be ready off the shelf or have a several week lead time. FISCAL IMPACT This project is not funded in the current budget. However, City Council previously directed staff to use ARPA Funding for the unanticipated expense. The total estimated cost for the project including design, construction, and administration is between $1,000,000 to $1,250,000. RECOMMENDATION Replace the northeast and northwest retaining walls of the North Shore Road Bridge approach with Lock+Load MSE walls, or similar. This is an economic solution that should provide structural stability and complement the existing retaining walls on the south side of the bridge. Authorize the City Manager to amend the public improvement contracts with DOWL and Emery & Sons to construct the designed walls. Reopen Northshore Road to vehicular traffic upon completion. ATTACHMENTS 1. Northshore Road Bridge— NE Retaining Wall Findings and Recommendations, DOWL 503.635.0215 380 A Avenue PO BOX 369 Lake Oswego, OR 97034 www.lakeosweao.citv ATTACHMENT 1 RESOLUTION 21-41 A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF LAKE OSWEGO APPROVING REPAIRS TO THE NORTH SHORE ROAD BRIDGE WHEREAS, City staff has evaluated the condition of the retaining wall on the northeast approach of the North Shore Road Bridge which was the cause for the closure that has been in place since July of 2021; and WHEREAS,City staff negotiated and executed contracts with DOWL(Engineering Consultant) and Emery & Sons (Contractor), who have expertise in retaining walls; and WHEREAS, the geotechnical and structural findings support replacing the retaining walls on the northeast and northwest approach with Mechanically Stabilized Earth (MSE) type walls; and WHEREAS, the North Shore Road bridge provides a critical alternate north-south route in the event State Street is blocked due to a crash, a stopped train, or construction. NOW,THEREFORE, BE IT RESOLVED by the City Council of the City of Lake Oswego that: Section 1. The northeast and northwest retaining walls of the North Shore Road Bridge approach be replaced with Lock+Load MSE walls, or similar. Section 2. The City Manager amend the public improvement contracts with DOWL and Emery & Sons to construct the designed walls. Section 3. The Northshore Road bridge shall be reopened to vehicular traffic upon completion of the replacement of the retaining walls. Section 4. Effective Date. This Resolution shall take effect upon passage. Considered and enacted at the regular meeting of the City Council of the City of Lake Oswego on the 21st day of December, 2021. AYES: NOES: EXCUSED: ABSTAIN: Joseph M. Buck, Mayor Resolution 21-41 Page 1 of 2 ATTEST: Kari Linder, City Recorder APPROVED AS TO FORM: Jason Loos, City Attorney Resolution 21-41 Page 2 of 2