2000 TOWER ST INDEX HALL 2023-12-29

AWN, •R ENGINEERING 4.8 SITE UTILITIES The following sections provide geotechnical recommendations for design and construction of new site utilities. Geotechnical recommendations include trench excavation and support, construction dewatering, pipe foundation support, pipe bedding, and trench backfill and compaction criteria. Please note, for any new utilities within public right-of-way, local standards will supersede the recommendations below. Trench Excavation and Support We anticipate excavations for underground utilities will primarily be within medium dense to dense fill/native soils. A heavy-duty, hydraulic excavator with sufficient reach should be able to excavate the proposed trenches to the expected depths. Upon reaching the trench bottom, we suggest that a smooth - bladed bucket be used to clean the bottom of loose and/or disturbed soil. The final trench bottom should be firm and free of loose and disturbed soil. Trench configurations and maintenance of safe working conditions, including temporary excavation stability, should be the responsibility of the contractor. All applicable local, state, and federal safety codes should be followed. Temporary excavations for utilities should meet the requirements detailed in Section 4.2 of this report. If groundwater seepage is present, flatter slopes, temporary shoring, and/or dewatering may be required. Appropriately sized trench boxes should provide adequate support for shallow excavations, provided the trench is properly dewatered and settlement -sensitive structures and utilities are not situated immediately adjacent to the excavation. Trench boxes should meet the requirements in Safety Standards for Construction Work, Part N ( WAC Chapter 296-155). Construction Dewaterine We anticipate perched groundwater may be encountered within the trench zone, particularly during winter and spring. If perched, water -bearing zones are encountered, construction dewatering can be achieved following the procedures in Section 4.2 of this report. Pipe Foundation Support Based on the conditions observed in our explorations, dense soils are anticipated at the base of utility trenches. The soil will provide adequate foundation support for utilities, provided the foundation soil remains in a relatively undisturbed condition. If the bottom of the trench becomes disturbed due to excavation and/or foot traffic during the laying of the pipe, the disturbed material should be overexcavated to expose undisturbed foundation soil. The overexcavation should be backfilled with suitable foundation material to provide a firm trench bottom. Foundation material should be free of roots, topsoil, lumps of silt and clay, and organic and inorganic debris. MP ENGINEERING, PLLC MPGEOTECH.COM 14