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n <br />536 <br />Designing with Geomembranes Chap. 5 <br />TABLE 5.18 MODIFICATION FACTORS AND REDUCTION FACTORS FOR GEOMEMBRANE <br />PROTECTION DESIGN USING NONWOVEN NEEDLE -PUNCHED GEOTEXTILES <br />Modification Factors <br />MFs <br />MFPD <br />MFA <br />Angular <br />1.0 <br />Isolated <br />1.0 <br />Hydrostatic <br />1.0 <br />Subrounded <br />0.5 <br />Dense, 38 mm <br />0.83 <br />Geostatic, shallow <br />0.75 <br />Rounded <br />0.25 <br />Dense, 25 mm <br />0.67 <br />Geostatic, mod. <br />0.50 <br />Dense, 12 mm <br />0.50 <br />Geostatic, deep <br />0.25 <br />Reduction Factors <br />RFCR <br />Protrusion (mm) <br />Mass per unit area <br />RFCBD <br />(g/m2) <br />38 - 25 <br />12 <br />Mild leachate <br />1.1 <br />Geomembrane alone <br />N/R N/R <br />N/R <br />Moderate leachate <br />1.3 <br />270 <br />N/R N/R <br />> 1.5 <br />Harsh leachate <br />1.5 <br />550 <br />N/R 1.5 <br />1.3 <br />1100 <br />1.3 1.2 <br />1.1 <br />>1100 <br />-1.2 =1.1 <br />-1.0 <br />N/R = Not recommended <br />Paso, = allowable pressure using different types of geotextiles and site-specific <br />conditions. <br />Based on a large number of ASTM 5514 experiments, an empirical relationship for <br />Patio, has been obtained, Eq. (5.33). It requires the set of modification factors and re- <br />duction factors given in Table 5.18. <br />Pallow-50 + 0.00045 N 1 l ( 1 <br />C <br />(5.33)MFS X MFPD XMFALRFCR X RFCBD <br />where <br />pail,,,~ = allowable pressure (kPa), <br />M = geotextile mass per unit area (g/m2), <br />H = protrusion height (m), <br />MFS = modification factor for protrusion shape, <br />MFPD = modification factor for packing density, <br />MFA = modification factor for arching in solids, <br />RFCR = reduction factor for long-term creep, and <br />RFCBD = reduction factor for long-term chemical/biological degradation. <br />Note that in the above all MF values , 1.0 and all RF values , 1.0. <br />'-a <br />