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GEOMEMBRANE PUNCTURE RESISTANCE AGAINST ROUNDED MODULES• NORTH COUNTY RECYCLING CENTER AND SANITARY 1.0 Introduction The final grading plan prepared as part of the expansion of the North County Recycling Center and Sanitary Landfill shows a maximum waste height of approximately 255 feet above the base of Module 5 through 11. Because of the significant waste height, a puncture resistance calculation has been performed to determine if a geotextile cushion is required above the geomembrane if rounded gravel is used in the leachate collection and removal system. The maximum grain size of the rounded gravel is assumed to be 3/8 inch or 9.5 millimeters (nun). 2.0 Calculations According to Koerner (1998), the allowable pressure (P'aliow) that can be tolerated by a geotextile layer subject to a protrusion of effective height H is given by, Pauaw = where, 50+0.00045 H I [— MF L s 1 1 MFPD . MFA RFcR . RFCBD (Eq. 1) P'allo , = Allowable pressure (in kPa) M = Mass per unit area of the geotextile cushion (in g/m2) H = Effective protrusion height (in meters) MFs = Modification factor for shape of protrusion MFPD = Modification factor for packing density MFA = Modification factor for arching FCR = Partial factor of safety for creep FCBD = Partial factor of safety for chemical and biological degradation Assuming a maximum waste height of 255 feet and a waste unit weight of 90 pcf, the actual pressure (Pact,d) on the geotextile is, P..A = (255 ft) x (90 lb/ft) = 22,9500 lb/fe z 1,100 kPa Koerner (1998) recommends a minimum factor of safety of 3 against puncture. The factor of safety (FS) against puncture is given by, ' P' FS = Parrow = a = 3 P."a 1,100 Therefore, P'wl, , = 3 x 1,100 = 3,300 kPa Page 1 of 2 N.IGEOTECXNICALWCRC&SL-20071Punture-ResistancelModules 5-111Rounded Gravel.doc