How do I check my factors of safety?

The "Reporting on Design" function lists any potential design problems identified by the software. Items considered are bending moment (compared with allowed sheet moment), toe smaller than recommended, danger of rotation in "no toe" designs and water levels. A check is also made on soil densities, and a warning is displayed if a submerged density seems large compared with the bulk density.

Other checks will be added as they are identified.

Note that Rules of thumb can be switched on/off in the Wall page of the define box. These can improve design safety.

I started working with SPW 911 and found that the passive earth pressure coefficient was not reduced by the reduction factor (R) as it is required by AASHTO Tables 5.5.2.C and 5.5.2.D.  Why not?

With cantilever walls, safety factors can be dealt with in several ways.  One of these is to divide the passive earth pressure coefficients by a reduction factors (typically 1.5 to 2.0.)  The other way is to compute the equilibrium condition for summation of forces and then add toe length.  SPW 911 uses the latter approach.  If you want to reduce the passive earth pressure coefficient, you can do so directly in the soils page.

Can the factor of safety (FOS) be set or changed? How is this done?

User can select Free Earth Support (FOS = 2) or Fixed Earth Support (FOS not applicable). User can enter a toe (including 0) manually. In all cases, FOS  can be calculated and displayed.  To change the factor of safety:

• Display the fos in the left margin.
• Open the "Wall" page.
• Switch "Automatic" off.
• Increase/Decrease the Toe until the desired fos is obtained.

I am designing a cantilever wall, and would like a factor of safety of 1.4.  Program determines the penetration based soil layers and rule of thumb.  I've tried adjusting K_pc value of embedments layer.  This increases the penetration but does not increase the factor of safety, and has a bad effect on the deflection at the pile top.  What's the best way to deal with this?

Open the "Wall" page, switch "Automatic" off, and enter the toe manually.

Is the factor of safety based upon net pressures, i.e. active minus passive pressures or can it be set separately for active and passive  pressures?

Net pressure.

"The Fine Print" for SPW 911

The information, including technical and engineering data, details, procedures and results, presented in this program have been prepared in accordance with recognized contracting and/or engineering  principles, and are for general information only.  While every effort has been made to insure its accuracy,  this information should not be used or relied upon for any specific application without independent  competent professional examination and verification of its accuracy, suitability and applicability, by a licensed professional engineer.  Anyone making use of this material does so at his/her own risk and assumes any and all liability resulting from such use.  The entire risk as to quality or usability of the data contained within is with the user.  In no event will Pile Buck^® International, Inc. be held liable for any damages including lost profits, lost savings or other incidental or consequential damages arising from the use of or inability to use the information contained within.  By continuing, the user of this program hereby agrees that the user has read the terms and conditions outlined in the attached "End User License Agreement" and "Disclaimer of Warranty and Limited Warranty" and agrees to be bound by the terms and conditions mentioned therein.  If the user is not in agreement with the terms and conditions outlined in the attached "End User License Agreement" and "Disclaimer of Warranty and Limited Warranty" in its entirety please return this program immediately for a complete refund of the original purchase price.

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