Geotechnical Evaluation report-2004

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� Aulik Associates Project BL-04-06716 October 11,2004 Page 7 layer of sand. In order to reduce curling and shrinkage of the concrete, alternate concrete mix designs may be required. This could include,but not be limited to,the addition of high range water reducers and changing to larger aggregate size. C.S.c. Subgrade Modulus. T'he anticipated floor subgrade is engineered clean sand fill. It is our opinion that a modulus of subgrade reaction, k, of 250 pounds per square inch of deflection(psi)may be used to design the floor with the anticipated sand subgrade. C.6. Below-Grade Walls We recornmend backfill placed on the exterior sides of the foundation wa11s in landscape areas be compacted to a minirnum of 90 percent of its standard Proctor maximum dry density. Beneath steps and slabs,it should be compacted to a minimum of 95 percent. If portions of the bacl�ill lie beneath pavements,it should be compacted to a minimum of 100 percent in the top 3 feet of subgrade. Debris-free soils from the footing excavations may be used as fill. Backfills should be brought up uniformly on both sides of the foundation walls to mi imi�.��splacement of the foundation walls. C.7. Egterior Slabs T'he previously-placed fill soils and swamp deposited soils are frost-susceptible soils. If these soils become saturated and freeze, 1 to 2 inches of heave may occur. This heave can be a nuisance for slabs or steps in front of doors and at other critical grade areas. One way to reduce this heave is to remove the frost-susceptible soils down to bottom-of-footing level and replace them with nonfrost-susceptible sand or sandy gravel. Sand or sandy gravel with less than 7 percent of the particles by weight passing a number 200 sieve is non frost-susceptible. If this approach is used and the excavation bottoxns terminate in non-free draining soils,we recommend a drain tile be installed to remove any water that may collect in the sand. The bottom of the subexcavation should be graded so the water flows to the center where it can be collected by the pipe and drained to a storm sewer, another drain tile, or a water collector system for discharge. An alternative method of reducing frost heave is to place a minimum of 2 inches of extruded polystyrene foam insulation beneath the slabs and extending about 4 feet beyond the slabs. The insulation will reduce frost penetration into the underlying subgrade and thereby reduce heave. Six to 12 inches of granular ma.terial is generally placed over the insulation to protect it during construction.