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FREEZING WEATI-iER EFFECTS ON BUII,DING CONSTRUCTION GEI�TERAI. Because wacer expands upon freezing and soils contain water, sous which are allowed to freeze will heave and lose density. Upon thawing, these soils will not regain their original strength and densiry. The excent of heave and densiry/ svength toss depends on the soil rype and moisture condition. Heave is greater in sails with higher percentages of fines (silts/clays). High silt content soils are most susceptible, due to their high capillary rise po�ential wliich can create ice lenses. Fine grained soils generally heave about 1/4" [0 3!8" for each faot of frost penetration. T'his can transiate to 1" to 2" of totai fros[ heave. This total amount can he significandy greater if ice Iensing occurs. DESIGN CONSIDERATIONS Clayey and siity soils can be used as perimeter bacl�ill, although the effect of their poor drainage and frost properties should be considered. Basement areas will have special drainage and lateral load requirements which are not discussed here. Frost heave may be critical in doorway areas. Stoops or sidewalks adjacent to doorways could be designed as structural slabs supported on frost footings with void spaces below_ With this design, movements may then occur between tEie s�uctural slab and the adjacent on-grade slabs. IVon-frost susceprible sands (wit6 less than 12% passing a#200 sieve) can be used below snch areas. Depending on the function of surrounding areas, the sand layer may need a thicl�ess transirion away from the area where movement is critical_ With sand placement over slower draining soils, subsurface drainage would be needed for the sand layer. High densiry extruded insulation could be used within the sand to reduce frost penetration, thereby reducing the sand thickness needed. We caurion that insulation placed near the surface can increase the potential for ice glazing of the surface. T'he possible effects of adfreezing should be considered if clayey or silty soils are used as bacl�ill. Adfreezi.ng occurs when backfill adheres to rough surfaced foundation walls and Iifts the wall as it freezes and heaves. This o�currence is most common with masonry block walls, unheated or pooriy heated building situa�ions and ciay backfill. The potenrial is also increased where bacl�ill soils are poorly compacted and become saturated. The risk of adfreezing can be decreased by placing a Iow fricpon separating layer between the walt and backfill. Adfreezing can occur on exterior piers (such as deck, fence or other similar pi�r footings), even if a smooth surface is provided. This is more likely in poor drainage situations where soils become saturated. Additional foodng embedment and/or widened footings helow the frost zones (which includes tensiie reinforcement) can be used to resist uptift forces. Specific designs would require individual analysis. CONSTRUCTION CONSIDERATIONS Foundations>slabs and other improvements which may be affected by frost movements should be insulated from frosc penetrarion during freezing weather. If filling takes place during freezing weather, all frozen soils, snow and ice should be stripped from areas to be filled prior to new fill placemen[.The new fill should not be allowed to freeze during transit, placement or compaction. This should be considered in the project scheduling, bud�eting and quantiry estimating. It is usually beneficial to perform cold weather earthwork operations in small areas where grade can be attained quickly rather than working larger areas where a greater amount of frost stripping may be needed. If slab subgrade areas freeze, we recommend the subgrade be thawed prior to floor slab placement. The frost action may also require reworking and recompaction of the thawed subgrade. Q i REP015(2/�I} AMERICAN ENGINEERING 1'ESTIlVG, INC.