1318 W MUKILTEO BLVD 2016-01-01 MF Import

Wrought Corporation JN 06287 August 11, 2006 Page 9 DRILLED CONCRETE PIERS Drilied, concrete-filled piers may be used, if it is uneconomical to excavate to bearing soil. Based on our exploralions, it appears that the piers can be constructed by open-hole methods. However, the drilling contractor should have access to casing or a slurry method, in case sloughing occurs in the loose near-surface soil. A wide variety of depths and pier diameters are possible, but we recommend using a minimum pier diameter of 16 inches. For a minimum embedment of 10 feet into the medium-dense or denser sand and a pier diameter of 16 inches, we recommend assuming an allowable compressive capacity of 25 tons per pier. Center-to-center pier spacing should be no less than three times the pier diameter. We recommend reinforcing each pier its entire length. This typically consists of a cage of rebar extending a portion of the pier's length, with a full-length center bar. The piers should be designed for an active soil pressure equal to that pressure exerted by an equivalent fluid with a unit weight of 45 pcf for a total depth of 8 feet beginning a; the top of existing ground. This soii pressure acts on two times the grouted pile diameter. An ultimate passive soil pressure equal to that pressure exerted by a fluid with a density of 450 pcf will resist the lateral movement of the soldier piles below the 8-foot depth. For long-term conditions, a safety factor of 1.5 sho� i � be spplied to the passive soil pressure for the design. This passive soil pressure also acts on two times the grouted pile diameter. SLABS-ON-GRADE The residence Floors can be constructed as slabs-on-grade atop the competent sand or on structural fill. The subgrade soil must be in a firm, non-yielding conc+ition at the time of slab construction or underslab fill placement. Any soft areas encountered should be excavated and replaced with select, imported structural fill. Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. All interior slabs-on-grade must be underlain by a capillary break or drainage layer consisting of a minimum 4-inch thickness of gravel or crushed rock that has a fines content (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. The onsite sand is suitable as capillary break if it does not contain organics or debris. As noted by the American Concrete Institute (ACI) in the Guides (or Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on-grade slab that will be covered by tile, wood, carpet, impermeable Floor coverings, or any moisture-sensitive equipment or products. ACI also notes that vapor retarders, such as 6-mil plastic sheeting, are typically used. A vapor retarder is defined as a material with a permeance of less than 0.3 US perms per square foot (ps� per hour, as determined by ASTM E 96. It is possible that concrete admixtures may meet this specification, although the manufacturers of the admixtures should be consulted. Where plastic sheeting is used under slabs, joints should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor 6arner should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.00 perms per square foot per hour when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. GEOTECH CONSULTANTS,INC.