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. . .� , . - PRECAUTIONS FOR EXCAVATING AND REFILLING DURING COLD WEATHER Tlie winter season in this area presents specific provlems for foundation construction. Soils whicli are allowed to freeze undergo a moisture volu,ne 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 shoutd not Ue allowed to penetrate into the soils be- low any proposed structure. IJeally, winter excavation should 'ue lunited to areas small enough to be refilled to a grade hi�her than footins grade on the sao�e day. Typically, these areas should Ue filled to floor grade. Trench- ing back down to unfrozen soils for foundation construction can then be performed just prior to footing place�nent. Tlie excavated trenches should oe protected from freezin� by means of iii- sulating or heating during foundation coustruction. Backfilling of the foundation trenches should ._ oe perfonned i�nmediately after the below�rade foundation construction is finished. In addition. any interior footin�s, or footin�s designed witl�out frost protection should be extended belo�� frost depth, unless adequate precautions are taken to prevent frost intrusion until the buildins ca,i ue enclosed and lieated. � - 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 attauied in one day's t'vne,frost can be expected to develop � overnigl�t. Tlie depth of frost penetration can ue minimized by leavine a layer of loose soil on top of the compacted material overnight. However,any frost which fonns in this loose layer, or sno�� which accumulates, should 'oe completely re�noved from the �11 area prior to compaction and ad- " 3itional soil placement. Frozen soils, or soiLs containina 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 a�nple periods of heating to allow thawing of ihe soil syste�n. Alternatively, t}ie frozen soils can be completel�• re�noved and oe replaced with an engineered fill. The floor s1aU areas should Ue checked at ran- do.n and representative locations for remnant areas of frost,and density tests should Ue performed to document fill eompaction prior to slab placement. . Due to the potential proUlems associated with fiil placement durinQ cold weather, any fillin� operations should be monitored by a full-time, on�ite soils technician. Full-time monitorinQ � aids in detecting areas of frozen material, or potential problems wiih frozen material within , the Fll, so that appropriate measures can be taken. Tl�e choice of fill material is particularl}� important during cold weather, since clean granular fill materials can be placed and compacted more efficiently than silty or clayey sails. In addition, greater �nagnitudes of heaving can be expected with freezin�of tl�e more frost susceptiUle silts and clays. _ If :nore specific frost infonnation or cold weatller data concerning other construction �naterials is required,please contact us. , � tw�n c�t4+test�nq � . a'+o�nowwerrx�taooracora�..+c . �l r�7n (1_�'�1