Concrete Pipe & Box Culvert Installation - Shaw Precast Solutions

ally inspected for rocks, frozen lumps, highly plasticclay or other objectionable material. If the excavatedsoil differs significantly from the intended backfillmaterial set forth in the plans, it may be necessaryto haul the unsuitable soil away and bring in selectbackfill material.TRENCHWATERIn the case where the water table is located inthe trench zone, dewatering methods must be employedto remove the water. The future location ofthe water table must also be considered due to itseffect on backfill material and the box section. Thepresence of water around the box could cause flotationof the box section, or migration of the backfillmaterial. Migration of soil should be prevented, asthe backfill is a means of support for the box.There are different methods that can be used toremove this water: pumping, ditching, and/or pipingof the water. It should be noted that all pumpingshould be through a filtered discharge.BEDDING/GRADEPrecast reinforced concrete box sections are designedfor installed conditions rather than test conditions.Designs are presented in ASTM StandardsC 1433(M) and C 1577(M), and AASHTO M 259(M)and M 273(M). Bedding details for box sectionsare as illustrated. A proper foundation for a box culvertconsists of specified bedding material havinguniform flat surface characteristics (no low or highpoints), as these could create stress concentrationsin the box after installation. The box, once installed,will not normally settle; it cannot be forced down tograde. Coarse bedding materials are not beneficialdue to their irregular shape and sharp angles; insteadmedium to fine granular material should be70American Concrete Pipe Association • www.concrete-pipe.org