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XSTABL v5 An Integrated Slope Stability Analysis Program for Personal Computers

DESCRIPTION OF XSTABLXSTABL provides an integrated environment for

performing slope stability analyses on an IBM personalcomputer, or compatible. The program combines an intuitiveuser friendly interface and the analytical philosophy behind thepopular slope stability program, STABL, developed at PurdueUniversity. An analysis may consist of a search for the mostcritical failure surface or the determination of the factor ofsafety of a single surface with one of the many rigorous limitequilibrium methods incorporated into XSTABL. With each

analysis, graphical screen plots may be saved for later printingor for inclusion into other software applications such as wordprocessors. The integrated menu-driven interface providesintuitive access to descriptive tables for data entry, allowing theuser to enter, edit or review slope data quickly. Whileassembling the data, the user may view the slope geometry andaccess context-sensitive help. It is expected that this approachwill minimize potential errors and provide a more appropriatedata preparation method for the less familiar user.

MAIN MENUFigure 1 presents the opening menu that a user

will encounter upon starting XSTABL. In thisparticular menu the option: "LOAD DATA FROMDISK" is currently highlighted, and ready forpossible selection. As each option is highlighted, ashort description of each selection is provided belowthe menu-box for the convenience of the user.

If additional information is required, pressingthe F1 key allows the user can obtain extensivecontext sensitive help at all stages. The availableselections are also completely described in theXSTABL Reference Manual. This opening menurepresents the control center of the program andallows users to prepare datafiles, perform analysesand, if necessary, copy, delete, print, rename or viewXSTABL files without exiting the program.

PREPARE SLOPE DATA MENUWith this option selected, XSTABL presents the

user with the screen shown in Figure 2. From thismenu the user prepares all data for defining thegeometry of the slope, water surfaces and crackedzones as well as assigning soil strengths and selectingthe appropriate analytical method. Externalsurcharge loads, limiting boundaries and differentstrength types that include anisotropic, undrained andnonlinear Mohr-Coulomb strength envelopes are alsoavailable for advanced slope stability analysis. Dataoptions are selected by moving the cursor horizontallyand vertically through the available menus. If any ofthe options are selected in this particular menu, theuser is then prompted for numeric data for developingan input file for use with the slope stability analysisportion of XSTABL. A description of each option,as it is highlighted, is shown below the menu andadditional information is available via the F1 key.

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DATA TABLESAs an example, the data table for entering soil

properties is shown in Figure 3. The cursor keyscontrol movement between the columns and rows ofthe table, allowing the user to enter new data or editexisting values. Also, lines may be inserted, ordeleted from these tables. The descriptive nature andinstinctive sequences of data entry into these tables(almost) precludes the use of a "User-Manual". Context sensitive help is available from all datatables and provides relevant information about therequired content of each data table and theparameters required for slope stability analysis.

English or metric units can be readilyaccommodated by XSTABL. Information about theselected units is written to the created data file, thusensuring that the correct units are automatically set ifthe file is read again.

SLOPE GEOMETRY PREVIEWThe assembled slope geometry can be quickly

viewed on the screen monitor by pressing the F2 keyfrom any menu or data table. This allows the user toconstantly review the slope geometry as data isentered for the surface or subsurface boundaries,surcharge loads and the upper or lower limitingboundaries.

A typical example is shown in Figure 4. Such adisplay provides a quick summary of the informationcontained in a complete, or partially complete, datafile. This is a truly valuable feature of XSTABL andgreatly helps in reducing common slope geometryerrors. Also, it may be used to quickly review theslope geometry contained in previously created datafiles.

ANALYTICAL FEATURESThe Generalized Limit Equilibrium (GLE) method has

been implemented into XSTABL. This method allows factorsof safety to be calculated for force and moment equilibrium orfor force equilibrium only, using different interslice force angledistributions. With this approach, the user can readily calculatethe factor of safety according to Spencer’s, Morgernstern-Priceor one of the methods proposed by the Corps of Engineers.

If an analysis requires a search for the most critical failuresurface, the simplified Bishop and Janbu methods of analysisare selected due to their relative ease of use. The program maybe used to either search for the most critical circular,noncircular or block shaped surface or alternatively, used toanalyze a single circular or non-circular surface. The criticalsurface is identified by automatically generating and analyzingfailure surfaces between defined initiation / termination rangesor by connecting points randomly located within search boxesspecified by the user. This approach minimizes the required

input parameters and can be effectively used to confine thesurface generation within a narrow, well defined zone. The soilstrength along the failure surface may be described as eitherconventional (i.e. c, ), undrained or non-linear Mohr-Coulomband can be either isotropic or anisotropic. The undrainedstrengths are assigned as a function of the vertical effectivestress.

For effective stress analyses, pore water pressures may besimulated by specifying :

1. A piezometric surface 2. Multiple phreatic surfaces 3. Pore water Pressure Grid 4. Constant pore pressure 5. Pore pressure parameter, ru

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GRAPHICAL OUTPUTDuring the analysis phase the user may elect to save the

slope geometry and failure surface plots, as viewed on themonitor, for printing at a later time. XSTABL supports thefollowing graphical formats:

1. Internal (XSTABL) 2. WordPerfect Graphics Format (WPG) 3. Hewlett Packard Graphical Language (HPGL)

The internal format files are intended for printing on anIBM graphics compatible 9 or 24-pin dot-matrix printer (e.g.

EPSON FX-85), HP LaserJet, or a HP Plotter (e.g. HP-7475A). The other formats, WPG or HPGL, may be imported intopopular word processors (e.g. WordPerfect, Word or AmiProfessional), desktop publication applications or generaldrawing programs (e.g. AUTOCAD) for direct inclusion intofinal reports or project drawings.

Figure 5 illustrates the use of the WPG format file printed,as part of this document, using the DOS word processorWordPerfect 6.0. The ability to include plots, such as Figure 5or 6, within a final report is a major asset.

STABILITY ANALYSIS OUTPUTThe input data, warning messages, possible errors and the

results of the stability analysis are all written to the XSTABLoutput file. This output file, in conjunction with any saved plotfiles, provides the user with complete documentation for eachstability analysis. If a search for a critical surface is performed,a summary table listing the ten surfaces with the lowest Factorof Safety is included in the output. This table is suitablyformatted for direct inclusion into reports prepared using a wordprocessor. A time and date stamp, as well as the filename, areincluded in the input, output and plot files for easier cross-referencing and final documentation.

If a single surface is analyzed, considerable data regardingthe slice dimensions and the forces (or stresses) acting on theslice boundaries are written to the output file and plotted in theformat shown in Figure 6. This extensive information is

presented to allow the user to check the computed results aswell as for assessing the reasonableness of the reported factor ofsafety for the rigorous methods.

ERROR CHECKINGXSTABL checks for erroneous input data prior to analysis.

If errors are detected, a descriptive error message is written tothe output file to help the user make the necessary correction. This error message does not require the user to refer to theReference Manual even though a complete listing of all errormessages is proved for informational purposes. As a furthercheck, the user has an option to view the input slope geometrybefore the start of the calculation stage, and if any geometricerrors are noticed, the analysis can be stopped so that the usercan make the necessary corrections.

Figure 6

PROGRAM AVAILABILITY

A license to use a fully operationalversion of XSTABL on a single computeris available at a cost of US$ 450.00. Thislicense fee includes telephone support andthe option for future upgrades at anominal charge for registered users. Fororganizations interested in licensingmultiple copies, a special discounted rateis available. A demonstration or testversion of XSTABL is also available toprospective users at a cost of $25.00 (withmanual), which may be applied towardsfinal purchase. The complete program, orthe latest demonstration version, may beordered by contacting Dr. Sunil Sharma(208-885-6403) or by writing to:

Interactive Software Designs, Inc.953 N. Cleveland StreetMoscow, ID 83843, U.S.A.

MINIMUM HARDWARE REQUIREMENT

1. An Intel-PC, MS Windows OS, a CD drive (forinstalling the software); at least 440 kb ofavailable RAM in DOS.

2. For hardcopy output, an IBM graphics compatibledot-matrix printer, HP LaserJet (with at least 1.5Mb of RAM) or a HP Plotter is required forprinting the internal (XSTABL) graphics files.

Please note that files created in WPG or HPGLgraphical formats will require additional third partysoftware for final hardcopy printing. For increasedcomputational speed XSTABL automatically uses afloating point coprocessor (80x87), if installed.

For best results, a computer system with a hard-disk, coprocessor, VGA adaptor and a color monitor isrecommended for effective use with XSTABL.

02/28/07