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North County Library Addition <br />1001 County Road #512, Sebastian, Florida <br />GFA Project No. 20-9197.00 <br />Geotechnical Exploration Report <br />April 24, 2020 <br />Page 7 of 10 <br />method (ASTM D 1556). Hand Cone Penetrometer (HCP) tests can also be performed to <br />evaluate compaction. <br />Our recommendations for preparation of the site for use of shallow foundation systems and on - <br />grade slabs are presented below. This approach to improving and maintaining site soils has <br />been found to be successful on projects having similar soil conditions. <br />Initial site preparation should consist of removing vegetation, topsoil, near surface roots, and <br />other miscellaneous debris within and to a distance of 5 feet beyond of the planned <br />construction limits. Foundations and the below grade remains of former structures within the <br />footprint of the new construction should also be removed. Similarly, utility lines within the <br />limits of the proposed construction should be removed or properly abandoned so that they <br />will not adversely impact overlying structures. <br />2. Following site stripping and prior to placing fill, areas of surficial sand should be compacted <br />(proof rolled) and tested. We recommend using a steel drum vibratory roller with sufficient <br />static weight and vibratory impact energy to achieve the required compaction. Density tests <br />should be performed on the proof rolled surface at a frequency of not less than one test per <br />2,500 square feet, or a minimum of three (3) tests, whichever is greater. <br />3. Fill material may then be placed for the building pad and general site grading, as required. <br />The fill should be inorganic (i.e., contain less than 5 percent by weight organic materials) <br />and classified as SP, SW, GP, GW, SP -SM, SW -SM, GW -GP, or GP -GM. GFA does not <br />recommend using fill materials having silt/clay-size soil fines contents exceeding 12 <br />percent. Fill should be placed in lifts having a maximum thickness of 12 -inches. Each lift <br />should be compacted and tested prior to the placement of the next lift. Density tests should <br />be performed within the fill at a frequency of not less than one test per 2,500 square feet per <br />lift in building areas, or a minimum of three (3) tests per lift, whichever is greater. <br />4. For foundations placed on structural fill or compacted native granular soils, the bearing <br />subgrade should be tested for compaction and observed by an engineer or geologist or <br />his/her representative to determine if the soil is free of organic and/or deleterious material. <br />Density tests should be performed at a frequency of not less than one (1) density test per <br />each isolated column footing and one (1) test per each seventy-five (75) lineal feet of wall <br />footing. <br />5. During fill placement and compaction, GFA does not recommend using full-size vibratory <br />rollers within 5 feet of the walls of the existing library building. Within this zone, the loose lift <br />thickness of the fill should be limited to 6 inches and compaction should be performed using <br />portable equipment, such as hand operated plate tampers, rollers, or jumping -jack <br />compactors. <br />6. The contractor should consider the final grading contours contained in the project plans <br />when executing backfilling and compaction operations. <br />