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Subsurface Exploration and Foundation Evaluation Proposed Golden Oil Refueling Station Stoughton, Wisconsin PSI Project No. 0092822 Page 14 *Defined in NR 151.002(14r) as a "soil that has at least a 3-foot deep layer with at least 20 percent fines; or at least a 5-foot deep layer with at least 10 percent fines; or an engineered soil with an equivalent level of protection as determined by the regulatory authority for the site." The information presented above is provided as general guidance for considering stormwater management in conjunction with the encountered subsurface conditions. However, Chapter NR151 of the Wisconsin Administrative Code, the Site Evaluation for Stormwater Infiltration (1002) document, or other applicable references must be consulted for appropriate site specific stormwater design guidance and requirements. PAVEMENT DESIGN RECOMMENDATIONS Pavements for this project are understood to consist of asphalt parking and drive areas, which will primarily be subjected to high volumes of passenger and semi-truck traffic. Specific traffic loading design details were not known at the time of this report. However, for the purpose of this analysis, an estimated average daily traffic loading of 145-18-kip ESALs/day was estimated. When traffic loading details are finalized, they must be discussed with PSI to determine if a re-evaluation of the recommendations contained herein is warranted. The pavement subgrade soils encountered at borings B-5 through B-7 consisted of silty sand and silty clay. The silty clay soils, with the poorer support characteristics, have been assigned an estimated visual AASHTO classification of A-6. The silty clay soils are generally rated as poor for pavement subgrade support based on their high shrink-swell potential, moderate to high frost susceptibility, poor drainage characteristics, and their high potential to soften when exposed to moisture. A frost index of F-3, a design group index of 14, a soil support value (SSV) of 4.0, and a subgrade modulus of 150 pci was used for this analysis. In order to use this value, all new fill used to raise low areas must have pavement support characteristics that are equal to or better than the existing soils. During construction, the surficial subgrade soils can become wet, softened and disturbed from rainfall and construction equipment. Therefore, prior to placing the pavement base materials, the subgrade must be recompacted and proofrolled. Particular attention should be given to high traffic areas that have become rutted and areas of backfilled trenches. Localized wet, soft, or unstable areas can be undercut to such depths determined necessary in the field to reach stable materials, and the area backfilled with crushed stone, such as 1% or 1% inch traffic bond (Section 305 of the State of Wisconsin Standard Specification for Highway and Structure Construction). If relatively large or thick zones of extensive yielding are observed, and normal discing and recompaction procedures cannot stabilize them, undercutting and replacement with crushed stone and geotextile fabric (if needed) may also be required in these areas. Preparation of the pavement subgrade must be performed as outlined in the Site Preparation section of this report. In view of the estimated traffic loading, and subgrade soils for this project, analysis of the proposed pavement and recommended pavement section were based upon a 20-year design life, regional factor of 3.0 and terminal serviceability of 2.0. The following table presents the recommended thickness for a flexible pavement structure on a properly prepared silty clay subgrade, along with their recommended structural coefficients. As previously noted,