10-26-1994 Council Agenda - Laserfiche WebLink

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PRECAUTIONS FOR EXCAVATING AND REFILLING DURING COLD WEATHER The winter season in this area presents specific problems for foundation construction. Soils which are allowed to freeze undergo a moisture volume expansion, resulting in a loss of density. These frost-expanded soils will consolidate upon thawing, causing settlement of any structure supported on them. To prevent this settlement, frost should not be allowed to penetrate into the soils .be- low any proposed structure. Ideally, winter excavation should be limited to areas small enough to be refilled to a grade higher than footing grade on the same day. Typically, these areas should be filled to floor grade. Trench- ing back .town to unfrozen soils for foundation construction can then be performed just prior to footing placement. The excavated trenches should be protected from freezing by means of in- sulating or heating during foundation construction. Backfilling of the foundation trenches should oe performed immediately after the below-grade foundation construction is finished. In addition. any interior footings, or footings designed without frost protection should be extended below frost depth, unless adequate precautions are taken to prevent frost intrusion until the building can oe enclosed and heated. In many cases, final grade cannot be attained in one day's time. even though small areas are work- ed. In the event final grade cannot be attained in one day's tithe, frost can be expected to develop overnight. The depth of frost penetration can be minimized by leaving a layer of loose soil on top of the compacted material overnight. However, any frost which (onus in this loose layer. or snow which accumulates, should be completely removed from the fill area prior to compaction and ad- ditional soil placement. Frozen soils, or soils containing frozen material or snow should never be used as fill material. After the structure has been enclosed, all floor slab areas should be subjected to ample periods of heating to allow 'thawing of the soil system. Alternatively, the frozen soils can be completely removed and oe replaced with an engineered fill. The floor slab areas should be checked at ran- dom and representative locations for remnant areas of frost, and density tests should be performed to document fill compaction prior to slab placement. Due to the potential problems associated with fill placement during cold weather, any filling operations should be monitored by a full -time, on -site soils technician. Full -time monitoring aids in detecting areas of frozen material, or potential problems with frozen material within the 1111, so that appropriate measures can be taken. The choice of 1111 material is particularly important during cold weather, since clean granular fill materials can be placed and compacted more efficiently than silty or clayey soils. In addition, greater magnitudes of heaving can be expected with freezing of the more frost susceptible silts and clays. If more specific frost information or cold weather data concerning other construction materiaLs is required, please contact us. PROF[ Page 63 INSULTANTS I Nc OR ROR A 1 1)