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PART FOURThe Design ProcessCOULOMB - NCMA-SLIDINGDriving ForcesThe horizontal earth pressure components, (P a + P q ) cos(δ), are the driving forces.Resisting ForcesGravity wall analysis calculates inter-unit shear, unit to leveling pad shear, leveling pad shear resistancebased on the weight of wall, Wf.Reinforced soil wall analysis calculates soil to soil sliding resistance (W f + W 1 + W 2 ) tan φ of the weakersoil (reinforced or foundation) as the resisting force. The 3rd edition of the NCMA Design Manual nowpermits the inclusion of vertical earth load components at the designer’s option.Note:Live load doesnot contribute toresisting forces.RANKINE - AASHTO-SLIDINGDriving ForcesThe horizontal earth pressure components, (P a + P q ) cos(β), are the driving forces in ASD/FS analysis.The factored horizontal earth pressure components, (EH d P a + ES d or LL d P q ) cos(β), are the driving forcesin LRFD analysis.Resisting ForcesGravity wall analysis must calculate inter-unit shear, unit to leveling pad shear, and leveling pad shearresistance.Reinforced soil wall analysis calculates sliding resistance as (W f + W 1 + W 2 + P av + P qv ) tan φ of the weakersoil in ASD/FS analysis.The factored sliding resistance is RF sl (EV r W f + EV r W l +EV r W 2 +EH d P av +ES r P qv (dead)) tan φ of theweaker soil in LRFD analysis.The reinforced soil wall sliding analysis becomes more complicated with geosynthetic sheetreinforcement because sliding must be checked along the lowest levels of reinforcement, as well asat the base of the mass (see Figure 4:10).4.12