Overview of MICHBACK Version 1.0 for DOS

What is MICHBACK?

MICHBACK is a computer program for the backcalculation of flexible and composite pavement layer properties using data obtained with a falling weight deflectometer (FWD).

The development of MICHBACK Version 1.0 for DOS was supported by the Michigan Department of Transportation and the University of Michigan Transportation Research Institute.

Strengths of MICHBACK

MICHBACK has many user-friendly features and advantages over other backcalculation programs. It:

• is menu-driven
• has on-screen forms to facilitate data entry, with error trapping
• allows the use of English or SI units
• can accommodate up to 10 FWD sensors
• can read files created by the KUAB FWD, or appropriately formatted ASCII files
• displays a graphical preview of sensor data contained in FWD files
• allows preprocessing of FWD data
• detects and reports suspicious FWD drops
• can backcalculate at any number of stations in a single run, or backcalculate using the "representative" or average deflection basins
• can backcalculate the "stiff layer" depth or one layer thickness in addition to the layer moduli
• can graphically display profiles of backcalculated moduli

Computer Requirements

MICHBACK Version 1.0 for DOS requires the following hardware and software:

• MS-DOS Version 3.0 or higher
• 640 KB of memory (RAM) with at least 550 KB of free memory
• A hard disk
• A color graphics adapter (CGA, EGA or VGA) and compatible monitor

Although not strictly required for the use of the program, the following hardware is strongly recommended:

• 486 or later PC
• math co-processor
• printer

Package Components

The following files are included in this distribution of MICHBACK:

1. readme.txt - An ASCII file containing an overview and installation instructions.
2. copyright.txt - An ASCII file containint the end user agreement.
3. michback.exe - The executable backcalculation program.
4. mbmanual.pdf - Adobe PDF file containing the user's manual. This may be viewed/printed using the free Adobe Acrobat Reader software.
5. mbmanual.ps - PostScript file containing the user's manual. This can only be printed on a PostScript printer.
6. sample.dat - Sample input data file.
7. kuab.fwd - Sample KUAB FWD deflection data file created by the KUAB software.
8. sample.out - Sample output file generated by using "sample.dat" and "sample.fwd."
9. sample.plt - Sample plot file corresponding to "sample.dat" and "sample.out."
10. ascii.fwd - An ASCII template for translating deflections measured by devices other than the KUAB FWD.

The supplied files can be used to generate screen images of most of the figures in the User's Manual without having to perform an analysis.

Configuring the Computer

Installation Procedure

To install the program on a hard disk, first make a subdirectory to hold the program (e.g., MD \MICHBACK), change to this directory (e.g., CD \MICHBACK), and copy all the files in the distribution to this directory.

The "config.sys" File

In the root directory, there is a file named "config.sys" which configures the PC system and loads any requested device drivers when the computer is turned on. The following statement will need to be added to the "config.sys" file, if it does not already exist:

  FILES=20

The MICHPAVE program uses a Fortran callable graphics package called GRAFMATIC. Unfortunately, this package is not compatible with the "ansi.sys" device driver used by some other programs for screen manipulations. Thus, if the "config.sys" file has the statement

  DEVICE=ANSI.SYS

then this statement will need to be removed and the computer re-booted (by simultaneously pressing the CTRL, ALT and DEL keys) before running MICHBACK. If available, use of an "ansi.sys" compatible device driver that can be unloaded from memory on demand is convenient since it eliminates the need to re-boot the computer.

Required Amount of Free Memory

The MICHBACK program requires about 475 KB of free memory to run. DOS and memory resident programs reduce the amount of free memory for use by other programs. The amount of free memory available can be checked by using the DOS command MEM or CHKDSK. If there is insufficient free memory, then memory resident programs will need to be removed before running MICHBACK.

If there is insufficient memory to load the program, a message similar to that shown below will be displayed:

  "Program too big to fit in memory."

Printing Graphics

Graphic screens produced by MICHBACK can be dumped onto an attached printer if the DOS command GRAPHICS.COM is issued after the computer is turned on and before MICHBACK is used. It may be convenient to include the command in the AUTOEXEC.BAT file so that it is issued every time the computer is turned on. To download graphics that are on the screen to the printer simply press the SHIFT and PRSCR keys simultaneously.

Backcalculation Method

MICHBACK uses a modified Newton method to backcalculate pavement layer properties using FWD data. In addition to the layer moduli, the depth of a stiff layer (e.g., bedrock) or the thickness of one layer may also be backcalculated.

Surface deflections are computed using an extended precision version of the well-known CHEVRON program. The numerical quadrature in the original CHEVRON program has been improved so that deflections of stiff pavements are computed accurately.

Details of the backcalculation method can be found in the following publications:

Harichandran, R. S., Mahmood, T., Raab, A., and Baladi, G. Y. (1993). "A modified Newton algorithm for backcalculation of pavement layer properties." Transportation Research Record, 1384, 15-22.

Harichandran, R. S., Mahmood, T., Raab, A., and Baladi, G. Y. (1994). "Backcalculation of pavement layer moduli, thicknesses and bedrock depth using a modified Newton method." In Nondestructive Testing of Pavements and Backcalculation of Moduli (Second Volume), ASTM STP 1198, H. L. Von Quintas, A. J. Bush and G. Y. Baladi (eds.) American Society for Testing and Materials, Philadelphia, PA, 68-82.

Future of MICHBACK

MICHBACK is being combined with the MICHPAVE nonlinear finite element program to provided a self-contained mechanistic pavement design system (MPDS) for the Windows 95/NT operating system. Overlay design, AASHTO thickness design and elastic layer analysis will be included within MPDS. MPDS is scheduled to be released in 1999 or 2000.