<br />22 <br /> <br />certerra.com 4660 Main Street, Suite 100, Springfield, Oregon 97478 T: 541.393.6340 <br />clays soils to shrink and swell. Note that the clay soils on this site, if exposed during the dry season (generally May <br />through October), should be covered with structural fill the same day they are exposed to help prevent them from <br />drying out. <br /> <br /> <br />Figure 6: Footing sketch showing recommended minimum 36-inch embedment of proposed <br />footing/structural fill underlying proposed footings. <br /> <br />Alternatively, proposed footings may be designed for a maximum net allowable soil bearing pressure of 4,000 psf, <br />when supported on a 4-inch-thick leveling course of properly compacted structural fill (as outlined in Section 3.3 of <br />this report) overlying the hard undisturbed Eugene Formation stratum. <br /> <br />The width of structural fill gravel used in footing excavations should be equal to the width of the footing plus the <br />thickness of the structural fill gravel beneath the bottom of the footing. For example, if the structural fill extends 1 <br />foot beneath the bottom of a 2-foot-wide footing, then the total excavation width should be 3 feet (1 foot of structural <br />fill plus 2-foot-wide footing). <br /> <br />The allowable soil bearing pressure is based on dead load plus design live load. The allowable soil bearing pressure <br />recommended above can be increased by one-third for short term wind or seismic loads. Minimum footing <br />dimensions should be in accordance with the provisions of the current International Building Code (IBC). <br />