2019-040 - Mainplace Mall Transformation

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MainPlace Mall Transformation Project 12126.001 The removal of existing artificial fill soils for subgrade of incidental improvements or foundations of incidental improvements not structurally connected to new or existing buildings should extend into competent fill to a depth of at least 1.5 feet below the finish subgrade or foundation bearing grade of the incidental improvements. The removal excavation should extend horizontally to a distance equals to the depth of the excavation below the subgrade or foundation bearing grade of the incidental improvements. Subprade Preparation The exposed excavation bottom should be scarified to a depth of at least 6 inches, moisture -conditioned to at approximately 2 to 4 percent above the optimum moisture content, and compacted at least 90 percent relative compaction as determined by ASTM Test Method D1557. Leighton should observe and test the excavation bottom to verify the vertical and lateral removal/excavation limits as local conditions may require additional removals. The proposed finish subgrade or foundation bearing grade can be reestablished by backfilling the removal excavation with compacted fill (i.e., engineered fill). Fill Materials and Placement The onsite soil less organics and deleterious materials are considered suitable for reuse as fill. Material larger than 4 inches in largest diameter should not be used in required fills. Expansion Index (EI) test results suggested that the near surface soils at the site exhibit very low expansion potential (i.e, EI=24 and EI=27 but greater than 20). However, clayey soils exist at the site and could be expansive when subject to change in moisture. Therefore, clayey soil when encountered during grading should not be used as fill near the proposed finish grade. Any required import material should consist of relatively non -expansive soils with an Expansion Index (EI) less than 20. 12 Leighton