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HomeMy WebLinkAbout2022-09-16 Kiwanis Park - Asphalt Parking Lot Restoration Memo.pdf 4815 Center Street Tacoma, WA 98409-2319 (253) 474-9449 / sittshill.com Brent K. Leslie, P.E., S.E. Kathy A. Hargrave, P.E. Larry G. Lindell, P.E., S.E. Michael A. McEvilly, P.L.S. Andrew J. Boileau, P.E., S.E. David C. Boileau, A.I.A. Memorandum To: Shawn Jensen, Principal, Bruce Dees & Associates Mike Faulkner, Senior Landscape Architect, Bruce Dees & Associates From: Don Davis, P.E., Senior Project Engineer, Sitts & Hill Engineers, Inc. Date: September 16, 2022 CC: Alan Wyatt, PPNR Capital Projects Manager, City of Renton Subject: Kiwanis Park – Asphalt Parking Lot Restoration On September 14, 2022, Sitts & Hill Engineers, Inc. (S&H) visited Kiwanis Park to observe the condition of the existing asphalt parking lot near the southwest corner of the property, and to meet with members of Bruce Dees & Associates (BDA), the owner, and contractor team. The purpose of the visit was to discuss the currently proposed pavement restoration method, and evaluate potential alternative restoration methods which could be pursued. Project Background: As part of the Kiwanis Park Improvements project, the City of Renton requested restoration of the existing parking lot. The intent of this restoration was to extend the life of the existing pavement structure, while also refreshing the appearance of the road to complement the new park facilities. BDA/S&H’s original design of the parking lot called for surface grinding 1-1/2 to 2-inches of existing asphalt, to be overlain with a proprietary asphalt reinforcement product called “GlasGrid”, and topped with 2” of new hot mix asphalt (HMA) pavement. During the early stages of design, this design was suggested to achieve two objectives: 1. Minimize the area of new or replaced impervious surface – by grinding and overlaying the existing parking lot, this work could be classified as pavement maintenance. This classification contrasts with “replaced impervious surface”, which, for an area as large as this parking lot, would trigger all site development minimum requirements per the City of Renton Surface Water Design Manual (SWDM). 2. Minimize the cost of construction for restoration of this parking lot – the design team considered the cost of the grind and overlay option to be less than a full replacement HMA pavement section. However, we did convey to the design team and owner that the grind and overlay method was not expected to achieve the same design life as a new pavement section. For an official determination of stormwater and development requirements of the parking lot surface, we connected with the City of Renton Development Engineering Manager, Brianne Bannworth, during the design phase of the project. From our correspondence, we determined that “Since the work with the southwest parking lot does not change the functioning characteristics of the facility, CED [Community and Economic Development Department] will consider the proposed work in the southwest parking lot as maintenance provided the impervious area is not expanded.” and “Any resurfacing performed on existing impervious surface can be considered maintenance.” See the full email from which the above statements were taken, included at the end of this memo. Page 2 of 3 These statements invalidated our first objective above, by allowing the designers to consider the improvements to the parking lot as “maintenance” rather than as “replaced impervious surface”, in the event that full depth replacement of the asphalt section was the option selected by the design team/owner. However, the design team continued to pursue the grind and overlay option due to the perceived cost savings. Current Conditions: Based on our conversations in the field with the contractors (Vern Orr and Chris Polk with Terra Dynamics, and Scott Stultz with Ground Up), we understand that the deterioration of the parking lot may have advanced since the time we initially observed the pavement and recommended the grind and overlay option. We have included photographs in this memo to document the current condition of the pavement. We observed widespread low to medium severity fatigue cracking (alligator cracking) and low to medium severity longitudinal/transverse cracking; as well as discrete instances of humps, particularly at the perimeter of the parking lot due to tree root growth beneath the pavement. Particularly concerning is a medium to high severity utility patch located above the existing 20” high pressure gas line through the entire lot. We observed alligator cracking and sagging at this location which may indicate that the pipe backfill and pavement subgrade were not properly prepared prior to placement of asphalt pavement. We were also informed that investigations by the contractor have revealed that the existing asphalt pavement thickness is limited to 2 – 2-1/2-inches. Suggested Course of Action: The contractor has proposed an alternative pavement restoration solution in favor of the currently proposed asphalt grind and overlay restoration method, originally proposed as a cost savings measure. The contractor’s proposed solution entails the following sequence of events: · Pulverize the existing pavement in place, material will remain on site and will serve as a granular base course for the new pavement section. · Perform minor grading activities to smooth the pulverized material, approximately matching the existing topography and drainage paths. · Recompact the base course/subgrade to meet compaction requirements for HMA pavement base course (95% maximum dry density, or firm and unyielding, adequately supporting a proof roll). o We would recommend a geotechnical engineer be present to observe the base course condition prior to paving. · If settlement is observed at localized areas during proof roll, base materials shall be over- excavated and replaced with structural fill and recompacted. o The coverage of these localized “soft spots” cannot be estimated, but must be resolved prior to paving as the base course dictates the structural effectiveness of the pavement section. · Install 3” minimum depth HMA pavement. o Existing pavement will be removed or ground down at the existing driveway so that the proposed full depth pavement section is flush with the existing pavement. Observations: We offer the following viewpoints in support of consideration of this alternative pavement method: Page 3 of 3 · The condition and thickness of existing pavement are not conducive to surface grinding – The contractor is doubtful that the existing pavement will stay intact during the grinding process, due to existing fatigue cracking of the pavement surface. · The remaining asphalt pavement will provide minimal structural benefit to the overlay section – Since the existing pavement is relatively thin, when the grind is complete a minimal thickness of asphalt will remain, and will not provide much structural benefit to the overall pavement section once the GlasGrid and overlay are applied. · The grind and overlay method is not a long term pavement solution – Even with a proprietary asphalt pavement reinforcement product, we would expect to see reflective cracking in the near to mid-term future (5-10 years). As stated above, this solution was chosen primarily as a cost savings measure, but we typically recommend full depth pavement replacement in lieu of repair. · The construction schedule is at risk with the currently proposed solution – The GlasGrid product is sensitive to temperature and moisture, and should be installed during ideal conditions in the summer months. However, paving of the parking lot at this time is not recommended since this is the sole construction access to the site, and will be subject to heavy truck loading well into the fall/winter months. The contractor is concerned about damage to the new pavement if construction vehicles are allowed to continue using this access. o If the city chooses to proceed with the grind and overly method, the contractor would propose to delay paving of the parking lot until such time that overlay with the GlasGrid product is appropriate (e.g., next spring). o If the grind and overly must proceed this year, the contractor would require a letter from the city accepting responsibility for construction traffic damage to the newly paved lot. · The proposed solution is a superior end product at a similar cost – The contractor expects the asphalt pulverization cost to be similar to the cost of grinding. The GlasGrid product is a fairly substantial cost for coverage of the entire parking lot. In the end, the contractor stated that the difference in cost for the proposed solution will not be substantially higher than the current solution. Recommendations: Ultimately, we support the contactor’s proposal to reconstruct the asphalt pavement section rather than restoring it with a grind and overlay option. With proper routine maintenance, it is our opinion that the reconstructed parking lot will result in long-term cost savings to the city, even if the initial cost of this solution is higher than the currently proposed solution.