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HomeMy WebLinkAboutAPPENDIX C.1_Civil_GeotechReport_PavementDesign rE Rawhide Engineering In g gInc. 6871 King Avenue West,Suite G1K,Billings,MT 59106(406)969-5305 February 3, 2022 Buffalo Run Bozeman, LLC 5400 Fowler Lane Bozeman, MT 59718 SUBJECT: Asphalt Pavement Sections Buffalo Run Streets Bozeman, Montana Dear Mr. Williams: This letter is for the asphalt pavement sections for the interior streets at the Buffalo Run Housing Project in Bozeman, Montana. Rawhide Engineering was requested to provide a pavement section for the interior streets based on our geotechnical investigation for the subdivision lots. The site soils consisted of topsoil and sandy lean clay to depths of 3 to 3.5 feet. The upper fine grained soils we underlain by gravel with sand and cobbles. At the time of our report, groundwater was at levels of 6.9 to 7.5 feet below existing site grades in February 2020. Rawhide Engineering calculated the esal's for Buffalo Run interior streets. We used the AASHTO Design for Flexible pavements to calculate the sections for this project. A CBR value of 3.5 was used for the design base on the sandy lean clay sample. The following are the sections which we have recommended. Pavement Sections The recommended pavement structural sections for the project presented below was calculated using the AASHTO pavement design procedure. Traffic loading information was estimated by Rawhide Engineering based on subdivision experience in similar soil conditions. We used loading conditions of 155,300 18-kip equivalent single axle load (18-kip ESAL) for the structural section for the lifetime of the pavement. A CBR value of 3.5 was used for design of the pavement section. The calculations included 1% heavy trucks. PAVEMENT STRUCTURAL SECTIONS Traffic Condition Recommended Minimum Structural Section Buffalo Run Interior Streets 3 inches of Asphaltic Concrete, 6 inches of 1 '/2" Crushed Base Course on 8 inches of pitrun gravel subbase It should be noted that the subgrade soils are likely to be prone to frost action during the winter and saturation during the wet spring months. The primary impact of frost action and subgrade saturation is the loss of subgrade and aggregate base strength. Pavement life will be increased if efforts are made to reduce the accumulation of excess moisture in the subgrade soils. Subgrade and Aggregate Base Subgrade Preparation -After completion of the utility trench backfill and prior to placement of aggregate base, the upper six inches of subgrade soil shall be uniformly compacted to at least 95% relative compaction. This may require scarifying, moisture conditioning, and compacting in both cut and fill areas. Aggregate Base - Aggregate materials shall meet the requirements of the appropriate sections of the"Standard Specifications"for 1 '/2 Minus Crushed Base Rock. The aggregate base materials must be approved by the Geotechnical Engineer prior to use. After the subgrade is properly prepared, the aggregate base shall be placed in layers, moisture conditioned as necessary, and compacted by rolling to at least 95% relative compaction. Asphalt Concrete Pavement Materials-Aggregate materials for asphalt concrete in light and heavy traffic areas shall conform to the requirements listed for Type B bituminous aggregates of the "Standard Specifications." Asphalt concrete mixes shall utilize asphalt cement meeting the requirements of Section 02510 of"Standard Specifications". The mix design shall be based on the Marshall Method. Placement and Compaction - The asphalt concrete material and placement procedures shall conform to appropriate sections of the "Standard Specifications." The asphalt concrete material shall be compacted to a minimum of 93% of the Theoretical Maximum Rice Specific Gravity. We appreciate this opportunity to be of service to you, and look forward to future endeavors. If you have any questions regarding this report or need additional information or services, please feel free to call the undersigned. Sincerely, RAWHIDE ENGINEERING, INC. Robert W. Kukes, P.E. Principal