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Subsurface Exploration and Foundation Evaluation Proposed Golden Oil Refueling Station ' Stoughton, Wisconsin PSI Project No. 0092822 Page 8 fill in trenches, or adjacent to foundation stem walls or retaining walls. Substantial importing of suitable granular fill may be required. Proper moisture control is essential to reduce the amount of compactive effort necessary to achieve the desired densities. This is especially true of clayey soils, where scarification and aeration may be required to achieve near - optimum moisture levels prior to compaction. A sheepsfoot roller is generally required for compaction of clayey soils, whereas a vibratory smooth drum roller is preferred for granular material. Small hand-operated compactors should be used in confined areas; granular fills are generally more readily compacted to the required densities in such applications. It is recommended that well-graded granular soils be utilized as backfill in new utility trenches and along side below grade walls to reduce the potential for consolidation and settlement of the fill. All fill soils must be placed and compacted under engineering controlled conditions, to provide suitable support for overlaying structures and roadways. Additional guidance can be provided at the time of construction in the selection process for grade-raising fill and trench backfill. Where excavations encroach upon or extend below the groundwater or perched zones, substantial subgrade instability and sloughing/caving of sidewalls can occur. Some overexcavation of softened or loosened soils, in conjunction with the use of a crushed stone working mat, may be necessary and may become extensive with the soft/low strength cohesive soils. Additionally, significantly widened excavations may result, or be required for stability. The selection of fill materials for various applications should be done in consultation with the soils engineer. Similarly, the evaluation of the subgrade and placement and compaction of fill for structural applications should be monitored and tested by a qualified representative of the soils engineer. Foundation Analysis The proposed structure may be supported by a conventional spread foundation system. However, based upon the planned finished floor elevation (EL. 875.0), the soils encountered within borings B-1 through B-3 at the approximate footing bearing elevations (EL. 873.5 and EL. 871.0 for interior and exterior footings, respectively) consist of existing fill, which is not considered to be suitable for foundation support. All footings must therefore be extended through the existing fill and any buried topsoil to bear upon underlying natural soils, encountered at a depth of about 6 feet (EL. 869.1 to EL. 868.5) in B-1, B-2, and B-3. Undercuts on the order of about 2 to 3 feet below frost depth, and up to about 5 feet below interior footings may be required. However, some variation should be expected. Spread and continuous wall footings bearing upon suitable natural soils, or upon compacted structural fill or lean concrete slurry used to replace unsuitable materials, may be designed for a net allowable soil pressure of 3,000 psf. The suitability of the existing soils for support of the proposed foundation must be determined by testing by a qualified geotechnical engineer during construction, utilizing static cone