This post is an extension of a previous post https://howtoengineer.com/retaining-wall-lateral-earth-pressure/

The spreadsheet will use the nomeclature found in NCMA’s Design Manual for Segmental Retaining Walls and Coulomb Theory.

See here:
Lateral Earth Pressure – Soil Basic 1 Geometry Sketch

Also here is a ‘fun’ spreadsheet where you can enter values in green columns. There are a bunch of graphs to show you how ka (the horizontal earth pressure coefficient will change with different values for backslope, effective friction angle, wall batter, and friction between wall and soil.

Earth pressure spreadsheet: Lateral Earth Pressure – Coulomb

Attached are a couple of TEDDS calcs that show the analysis of active and passive pressures based on Coulomb Theory. I am working on incorporating a berm distance into the passive equations and will probably present this in a seperate post. Using Coulomb equations for Toe slopes and backslopes should be used with caution and these conditions may warrant a Global (or slope) Stability Analysis!

Soil Evaluation NAVDAC DM – 7.2

Soil Evaluation – NCMA

Equivalent Slope

Another note: When there is a toe slope that passive pressure will be reduced a good reference for this condition is CALTRAN Trenching and Shoring Manual 2011 and NAVDAC DM 7.2 page 7.2-65 Figure 4 .

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