2021-8-24_COSV_Pete_Fisch
Community & Public Works Department Engineering Division – Bridge Program 10210 E Sprague Avenue Spokane Valley WA 99206
Phone: (509) 720-5000 Fax: (509) 720-5075 www.spokanevalley.org
August 18, 2021
Lori Barlow, AICP
Senior Planner City of Spokane Valley 10210 E. Sprague Ave. Spokane Valley, WA 99206
RE: Painted Hills Planned Residential Development DEIS Comments Dear Ms. Barlow,
This letter is being written in response to the Draft Environmental Impact Statement regarding the Painted Hills Planned Residential Development (PRD) and the proposed Painted Hills Flood Control Plans dated June 23, 2020. My concerns, as the City of Spokane Valley’s Bridge Program Manager, relate to the existing Thorpe Road Bridge, (SPOKV-4421) and the pre-fabricated box
culvert proposed on Thorpe Road at Station 19+00± for flood control.
The existing Thorpe Road Over Chester Creek Bridge, SID #08014700, was built in 1976 and has an Average Daily Traffic (ADT) of 1,800 (Nov. 2018), with 6.25% large vehicles. It is single span, Prestressed Concrete Multiple Web girder bridge, made up of seven units of rib deck. It is
two lane, 26.7 feet curb-to-curb, no sidewalks, and has 1.5 inches of asphalt overlaying the bridge
deck. Concrete footings are supported on timber piles. It has a Sufficiency Rating of 64.79. This bridge is currently open with no weight restrictions and currently serves mostly residential properties to the east of Dishman-Mica Road.
Current Condition:
This bridge has seen some deterioration over the past few inspection cycles, mainly at the web-to-flange interface, due to possible overloaded vehicles. In May of 2019, the girders were evaluated and it was found that the stresses due to the cracking do not change the weight rating of the structure carried out in April 2017. However, if there is continued use by overloaded vehicles as
suspected, weight restrictions might be warranted in the future. This is considered a Short Span
Bridge which makes it ineligible for Federal Funding when the bridge requires rehabilitation and/or replacement. Project Impacts: The most significant impact that is presented by the proposed development is the inadequacies of
managing the existing Thorpe Road Over Chester Creek Bridge. The detailed engineering information presented in the Painted Hills Flood Control Plans (Plans), with a Professional Engineering Seal dated June 30, 2020, indicate a widening of Thorpe Road over Chester Creek.
Painted Hills PRD DEIS Comments August 18, 2021 Spokane Valley Bridge Program Page 2 of 2
The widening of Thorpe Road, as shown on Sheet C3.12 of the Plans, is planned to be
accomplished by adding a box culvert to the existing Thorpe Road structure. It most definitely must be noted that the Painted Hills documents identify the existing structure as a box culvert when in fact, the existing structure is a pile-supported, short span, multiple web girder bridge as previously noted. As there are dissimilarities between the existing structure and the proposed
structure, Thorpe Road cannot be widened over Chester Creek in the manner proposed.
Additionally, as previously noted, the current girders are experiencing cracking and stresses likely caused by overloaded vehicles. This current loading may require that weight restrictions be placed on the bridge in the near future. As part of the project, the proponent intends to overlay the existing
bridge with 4 inches of asphalt pavement, whereby the current structure only has 1-1/2 inches of
asphalt pavement. This added asphalt, may overload the existing bridge to the point where bridge weight restrictions are required. Should the bridge have weight restrictions, the planned methods of construction for the PRD will require modifications.
Recommendations:
The existing Thorpe Road Bridge over Chester Creek cannot be widened in the manner prescribed in the proponents Plans, that is, the web girder bridge cannot be widened by adding a box culvert. With that being the case, it is recommended that the proponent replace the Thorpe Road Bridge (SPOKV-4421) in accordance the WSDOT Bridge Design Manual (LRFD) M23-50.20, dated
September 2020. It should also be noted, that the existing bridge cannot be widened using a similar
bridge structure due to the age and condition of the existing bridge. The replacement structure for Thorpe Road could either be a bridge structure or a box culvert. The design elements and requirements of the new structure must meet those outlined in the WSDOT
Bridge Design Manual (LRFD) M23-50.20, dated September 2020. In completing the design, the
proponent will need to take into all anticipated traffic and construction loading, which means a new load rating for the bridge will be established. As far as the proposed pre-fabricated concrete box culverts on Thorpe Road, Station 19+00± for
the over-flow storm water channel, the design shall follow the guidelines presented within the
WSDOT Bridge Design Manual (LRFD) M23-50.20, September 2020. Respectfully submitted,
Pete Fisch
Bridge Program Manager / Engineering Technician II