Appendix E: Trial Wedge Method for Designing External Stability Calculations

Choose Design Method

When the designer inputs a slope above that exceeds the maximum allowed under standard design methods for Static or Seismic designs, the following screen allow the designer to choose either the typical Mononobe_Okabe (M_O) method or the Coulomb Trial Wedge Method.

The M_O method automatically lessens the slope above to the maximum allowed and continues the calculations.

The Trial Wedge button sends the user to a detailed explanation screen allowing the designer to read a thorough description of the methodology.

Once the designer reads and understand the methodology they can click the hide button to proceed through the design. If after the design is complete and the user wishes to rerun the calculations using the M_O method, simply recalculate the section and choose the M_O method button to lessen the slope.

Designers Note: Any design that utilizes the Trial Wedge method has a slope above that exceeds the maximum unreinforced slope allowed. Based on this fact, the Internal Compound Stability (ICS) calculations must be run and the designer must also analyze the stability of the slope above in an independent global stability program such as ReSSA from ADAMA Engineering. It is strongly recommended that the designer reinforce the slope above with horizontal geogrid layer for required stability; number of grids, length, strength and spacing to be determined by the engineer of record.

For more information on the maximum allowed slopes above see the Allan block Engineering Manual.