I would like to know if this program is appropriate for designing braced cofferdams? Will it accommodate a water level differential and will it allow the use of empirical pressure diagrams?

• SPW 911 is suitable for designing braced cofferdams, as it allows the use of Terzaghi and Peck wall pressure profiles. It does allow a water differential but does not allow the use of empirical pressure diagrams.
  
  
• In designing braced cofferdams, however, keep in mind that SPW 911 does not compute base stability; this must be checked separately. Also, SPW 911 assumes that the wall pressure at the excavation level are continued below the excavation line. In the case of stiff clays, this means zero on the soil side of the excavation. If this is not desirable, an alternate method of computation can be found in NAVFAC DM 7.02. More information on Terzaghi pressure profiles and their application can be found in the Sheet Pile Design by Pile Buck.

Using Terzaghi design pressures, what do the factors m & a represent and can they be modified?

m - depends on soil properties; a - 0.2 or 0.4 for temp/permanent works; both can be changed Ref: Pile Buck Steel Sheet Piling Design Manual, pg 119 (uses 'n' instead of  'a')

I was designing a cantilever wall with Terzaghi earth pressure assumptions. My output looks strange compared to manual calculations. What's going on?

The Terzaghi pressure model is not really appropriate to cantilevers - it's best used to calculate strut loads in anchored excavations. When Terzaghi is selected, Rankine is used for the pressure below the excavation depth as no other method is documented. Terzaghi is not recommended for bending moment calculations.

In a design with multiple walers, how is the required toe calculated in granular soils?

When more than one support is present, the toe and load on the lowest frame are found by considering the lowest span as a singly supported wall. Loads on the frames above the lowest are found using the current load model. The load model can be by a) Area Distribution (as described in the Sheet Pile Design by Pile Buck) or b) the Hinge Method. The method used is selected in the Supports page of the box.