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<br /> SUBJECT: HDPE Pipe D esign <br />GOLDER Job Number: 933-2720 Made by BES Date: 8/25/94 <br />ASSOCIATES Ref: Checked: Sheet of <br /> Reviewed: <br /> FJ~Nam~: GipZ120.~g1 <br />CALCULATIONS: (cont.,) <br />- Design the pipe to withstand 'buckling' (longitudinal wrinkling of the pipe wail) <br />The pipe-soil system's critical buckling pressure is calculated <br />as follows: <br /> <br />where; Pcb =Critical buckling soil pressure at the top of the pipe, psi <br />E' =Soil modulus in psi, calculated as the ratio of the vertical soil <br />pressure to vertical soil strain at a specified density. <br />Pc =Hydrostatic critical collapse differential pressure, psi <br />- Need to calculate Pc <br />Pc=2.32*E/(SDR 3) <br />where: E =stress and time dependent tensile modulus of elasticity, psi <br />Calculate E by referring to chart 25, "Time Dependent Modulus <br />of Elasticity for Polyethylene Pipe -vs- Stress Intensity" <br />(Reference 2) <br />Enter the following parameters on the chart: <br />Stress = 730 psi <br />Use the 50 year time curve and: <br />E = 14400 psi <br />Pc = 25.10 psi <br />* For E', say that a crushed stone is used as backfill and is <br />compacted to 90% standard (AASHTO T-99) <br />E' = 3000 psi <br />Pcb = 219.53 psi <br />Safety Factor =Pcb / Pt <br />SF = 1.50 <br />