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� . <br /> ■ Mr. Charles Thompson <br /> Project BL-04-05907 <br /> � October 27, 2004 <br /> Page 9 <br /> � � <br /> � <br /> � We recommend that the vapor barrier be inspected immediately before the concrete is placed to identify <br /> � . and patch holes or other potential paths for moisture vapor migration. <br /> � We also recommended that moisture content and moisture vapor transmission tests be performed after the <br /> s concret�slabs have cured,but before flooring is installed. Flooring manufacturers typically recommend <br /> ■ upper limits for moisture vapor transmission that can be used to set schedules for flooring installation. <br /> � C.6.c. Subgrade Modulus. The anticipated floor subgrade is native alluvial soils and engineered fill. It <br /> , is our opinion that a modulus of subgrade reaction,k, of 100 pounds per square inch of deflection(psi) <br /> may be used to design the floor. <br /> , • <br /> , C.7. Exterior Slabs <br /> a C.7.a. Subgrades. We recommend the vegetation and topsoil be removed from beneath the proposed <br /> � slabs. Fills and backfills should be compacted to a minimum of 95 percent of the standard Proctor <br /> � maximum dry density. <br /> � C.7.b. Frost Protection. The silty sand and clay and silt soils are frost-susceptible soils. Any silts <br /> ■ should be removed to at least 2 feet below slab elevation. If these soils become saturated and freeze, 1 to <br /> 2 inches of heave may occur. This heave can be a nuisance for slabs or steps in front of doors and at <br /> � other critical grade areas. One way to reduce this heave is to remove the frost-susceptible soils down to <br /> , bottom-of-footing level and replace them with nonfrost-susceptible sand or sandy gravel. Sand or sandy <br /> gravel with less than 5 percent of the particles by weight passing a number 200 sieve is nonfrost- <br /> � susceptible. <br /> � <br /> An alternative method of reducing frost heave is to place a minimum of 2 inches of extruded polystyrene <br /> � foam insulation beneath the slabs and extending about 4 feet beyond the slabs. The insulation will <br /> � reduce frost penetration into the underlying subgrade and thereby reduce heave. Six to 12 inches of <br /> granular material is generally placed over the insulation to protect it during construction. <br /> � <br /> � A third alternative for reducing frost heave is to support the steps or slabs on frost-depth footings. A <br /> void space of at least 4 inches should be provided between the bottoms of the steps/slabs and frost- <br /> � susceptible soils to allow the soils to heave without affecting the steps/slabs. <br /> � <br /> , <br /> � <br /> � <br />