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Height of Fill Above <br />Structure (feet) <br />Load per foot of Pipe <br />(kips) <br />Pressure on Structure <br />(psf) <br />3 <br />4 <br />650 <br />5 <br />9 <br />1500 <br />10 <br />23 <br />3,800 <br />15 <br />32 <br />5,300 <br />20 <br />52 <br />8,650 <br />bearing pressure of 3,200 psf. Footings should be at least 4 feet wide and extend at least 2 feet <br />below lowest adjacent finish grade. A layer of compacted fill at least twice the footing width <br />should underlay the footing. Fill should be placed and compacted as described in Section 5.1 <br />above. <br />Resistance to lateral loads can be provided by passive resistance against the sides of <br />footings and frictional resistance along the bottom of footings. Use an allowable passive <br />pressure of 250 pounds per cubic foot (equivalent fluid pressure), and a friction coefficient of <br />0.35 for design. <br />Factors of safety for bearing capacity and lateral load resistance factors are 3.0 and 2.0 <br />respectively; no factors of safety or scaling factors have been applied to lateral earth pressure <br />recommendations. <br />5.3 Portal Exit Design Loads <br />A portion of the portal exit structure will extend through compacted fill. For design, use the <br />pressures provided in Table 2 for the indicated fill thickness above the structure. <br />From NAVFAC DM -7.1, So'l Mechanics, 1982, pp. 7.1 -185 <br />1 Pressures based on a width of 6 feet, and a soil unit weight of 130 pcf <br />5.4 Portal Access Road <br />6.0 References <br />Colorado Geological Survey, 2000, Geologic Map of the Hesperus Quadrange, La <br />Plateau and Montezuma Counties, Colorado, Open - File 00 - <br />Cutslopes resulting from grading of the portal access roads should be 1:1 or flatter. The <br />roadway subgrade should be prepared by scarifying the upper 6 inches, moisture conditioning the <br />scarified soils to within 2 percent of the optimum moisture content, and compacted to at least 95 <br />percent relative compaction per ASTM D1557 - 09. If additional roadway material is necessary, it <br />should be placed in layers 8 inches or less, and compacted as described. <br />Rule 6.5 Geotechnical Stability Technical Revision <br />Chief Portal <br />Table 2. Design Pressures on Portal Structure <br />for Various Heights of Compacted Fill <br />March 16, 2013 <br />Page 5 <br />