Laserfiche WebLink
AMERICAN ENGINEERING TESTING, INC. AET Project No. 22-00012 <br /> 6.7 Exterior Backfilling <br /> Where exterior entry slabs, sidewalks, and aprons abut the buildings, we recommend placing <br /> select non-frost susceptible(NFS) granular backfill around the exterior of the buildings to reduce <br /> the potential for frost heave of the slabs and sidewalks. We recommend a sand or sand and gravel <br /> mix having less than 5% passing the No. 200 sieve and less than 40% passing the No. 40 sieve. <br /> The NFS fill should be placed in thin lifts and compacted to at least 95% of the maximum <br /> Standard Proctor dry density. <br /> The zone of the NFS backfill should extend at least 2 feet beyond the edges of the entry slabs, <br /> and be tapered upward at a slope of 3 units horizontal to 1 unit vertical (3:1) to meet the <br /> naturally-occurring soil. The purpose of the tapering is to reduce the potential for abrupt slab <br /> displacement when zones farther away from the addition may heave during winter. The sand <br /> backfill must include a proper drainage system to remove infiltrating water. <br /> 6.8 Exterior Underground Utility Construction <br /> Excavations for underground utility construction will extend into the silty/clayey soils and <br /> topsoil that we found in our borings. When unconfined, these soils are very sensitive to <br /> disturbance by construction traffic and worker foot traffic. Where silty/clayey soils (USCS <br /> Classification of CL, ML, CL-ML) are present at the pipe invert, the soil at the bottom of the <br /> trench should be over-excavated to allow placement of a minimum of 4 inches of granular pipe <br /> bedding below the pipe. If the soils are soft and susceptible to disturbance workers' foot traffic, <br /> we recommend placing a geotextile separator fabric between the subgrade and the pipe bedding <br /> to reduce mixing of the subgrade and the bedding. If the contractor is not careful, excessive <br /> amounts of soil disturbance will occur, requiring remedial subcutting and backfilling. <br /> For pipe bedding material, we recommend a sand or sand and gravel mix with less than 12% <br /> passing the No. 200 sieve, such as Mn/DOT 3149.2B2. Pipe bedding should be carefully placed <br /> and hand-compacted under the haunches of the pipe, around the pipe, and to a minimum of 6 <br /> inches above the crown. As backfill is placed in the trenches, special caution must be given to <br /> Page 19 of 28 <br />