2710 14TH ST BLDG A Geotech Report 2023-12-29

' 4.5.3.Abandoning Utilities ' The following recommendations apply to abandoning underground utility pipes at the site prior to vertical construction: ' ■ All utility pipes greater than or equal to 8 inches in diameter and located below building areas may be left in place provided they are fully grouted. ■ All utilities less than 8 inches in diameter and located beneath building areas may be left in place provided that they are capped and/or plugged with grout. ■ Utility structures should be removed and associated pipes capped/plugged to prevent the movement ' of groundwater. ■ Utility pipes encountered outside of building areas during redevelopment activities should be plugged, capped, or removed to prevent movement of groundwater. iThe following recommendations apply to utility pipe issues arising during vertical construction: ■ Abandoned utility lines under proposed buildings should be identified during construction and the existing trench backfill should be removed and replaced as follows. Utility pipes and existing trench backfill located below planned foundations should be removed entirely and be replaced with structural fill or lean concrete. Utility pipes and existing trench backfill located below planned floor slabs should be removed and recompacted to a depth of 3 feet below the bottom of the slab. The excavations should be backfilled with structural fill compacted to at least 95 percent of the MDD per ASTM D 1557 for floor ' slab areas and foundations designed for a maximum allowable bearing pressure of 3,000 psf. ■ We recommend that storm water pipes not discharge onto slope faces. ' 4.5.4. Earthwork Subgrade Preparation Prior to placing new fills, pavement base course materials or gravel below on -grade floor slabs, subgrade ' areas should be proofrolled to locate any soft or pumping soils. Prior to proofrolling, all unsuitable soils should be removed from below building footprints and new hardscape areas. Proofrolling can be completed using a piece of heavy tire -mounted equipment such as a loaded dump truck. During wet weather, the ' exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should be removed and replaced with structural fill. After completing the proofrolling, the subgrade areas should be recompacted to a firm and unyielding condition, if possible. The degree of compaction that can be achieved will depend on when the construction is performed. If the work is performed during dry weather conditions, we recommend that all subgrade ' areas be recompacted to at least 95 percent of the MDD in accordance with the American Society for Testing and Materials (ASTM) D1557 test procedure (modified Proctor). If the work is performed duri ng wet weather conditions, it may not be possible to recompact the subgrade to 95 percent of the MDD. In this ' case, we recommend that the subgrade be compacted to the extent possible without causing undue weaving or pumping of the subgrade soils. ' Subgrade disturbance or deterioration could occur if the subgrade is wet and cannot be dried. If the subgrade deteriorates during proofrolling or compaction, it may become necessary to modify the proofrolling or compaction criteria or methods. 1 I GWENGINEERS� October30, 2019 Page 12 File No, 21288-002 00