3400 RIVERFRONT BLVD Geotech Report 2022-10-25

• • 3 inches over areas of the site where native vegetation has grown. Greater depths may be • necessary to remove localized zones of organic material or deeper root zones in looser upper , material. The actual stripping depth should be based on field observations at the time of construction. Stripping should extend at least 5 feet beyond the limits of proposed structural • areas. Stripped material should be transported off site for disposal or used as fill in landscaping • areas. . 6.3.2 Buried Debris • We understand that concrete foundations, debris, and other items from previous development • were buried at the site by the undocumented fill. It is possible that deep excavations at the site • could encounter these elements. If encountered, these elements could result in difficult • excavations and may need to be demolished. Demolition includes the complete removal of any slabs, walls, footings, and utilities that need to be removed. In addition, any remaining • monitoring wells or underground storage tanks should be abandoned in accordance with state • and local regulations prior to site development. Excavations left from demolition of existing development should be backfilled with compacted • structural fill as recommended in this report. The bottom of the excavations should be • excavated to expose firm subgrade. The sides of the temporary excavations should be cut into • firm material and sloped a minimum of 11/2H:1V. • 6.3.3 Undocumented Fill • Undocumented fill is known to exist across the site. However, the undocumented fill was • generally buried by the structural fill placed by Polygon in 2015. The structural fill was • compacted to a dense condition and should provide adequate support for footings, pavement, 411 and floor slabs that are founded in this material. • Where improvements will be founded below the structural fill in the undocumented fill, we • recommend that the upper 24 inches of subgrade beneath footings, pavement, and floor slabs • be properly compacted. Alternatively, the upper 16 inches of subgrade could be cement • amended. • 6.3.4 Subgrade Evaluation • A member of our geotechnical staff should observe the exposed footing, floor slab, pavement, • and driveway subgrade after stripping, excavation, scarifying and compaction, cement • amending, and placement of structural fill have been completed to confirm that there are no areas of unsuitable or unstable soil. The subgrade should be evaluated using moisture-density • testing, a hand probe, or proof rolling with a fully loaded dump truck (or similar heavy, rubber- • tired construction equipment). If soft, loose, or otherwise unsuitable soil is found at the • subgrade level, we recommend that the soil be over-excavated and replaced with structural fill. • 6.4 CONSTRUCTION CONSIDERATIONS • Trafficability of soil at the ground surface may be difficult during extended wet periods or when • the moisture content of the surface soil is more than a few percentage points above optimum. If • not carefully executed, the earthwork activities can create extensive soft areas, resulting in • • • G EODESIGN? 14 Polygon-128-01:09161 5 •