While the Monotube-Okabe (M-O) method is the standard used in the seismic design of segmental retaining walls, a trial wedge method may be utilized to investigate walls when the M-O method becomes limited due to slopes above. Using methods similar to a global stability model, the trial wedge method determines the weight of the soil wedge above the failure plan and the active earth pressure of the soil wedge acting at the back of the soil mass. The solution it provides is purely mathematical and understanding soil mechanics and the slope steepness limits is also important. The limitation to the steepness of a slope discussed in (ref. BP, Chapter 11.4) still apply, and if the designer chooses to utilize the trial wedge method for walls with slopes above that exceed the soil mechanic limits, they must review the slope stability in a global stability program and possibly reinforce the slope above the wall. For a greater discussion on the trial wedge method see Chapter 5, Seismic Design, in the
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