Department of Transportation


The PSSLOPE software assists in pile wall design by combining limited equilibrium stability analysis, the strain wedge model for soil/structure interaction, and a pile sizing routine. The program is LRFD compliant in that it internally factors the moment resistance by 0.9 and allows the driving load to be factored by the user.

The West Virginia Division of Highways (WVDOH) allows state and public users of the PSSLOPE software who have been properly trained in its use to design soldier pile walls for projects performed for the WVDOH. This software was developed for the WVDOH by Dr. Mohamed Ashour under the research project RP 213. Neither the WVDOH nor Dr. Ashour warrant the software, its manual, or the results to be free of defects. It is the user’s responsibility to check results and to assure the correctness and suitability of those results. All users are cautioned to save their work at regular intervals and to close the program at the end of a session. Also, the user should close and restart the program before finalizing their results as a check for consistent results. Given the above warnings, we find that the software is relatively easy to use, provides relatively accurate deflections, and is consistent with the results of other more complex methods of pile sizing. The software can be downloaded here. Detailed installation instructions accompany the download. The manual can be accessed from the top menu within PSSLOPE.

PSSLOPE has three modes by which the slip plane can be identified. The first mode allows a circular slip plane to be defined by entering three points on the slip plane. The second mode allows PSSLOPE to search for the weakest circular slip plane within user-defined ranges for where the slip plane intersects the ground surface. The third mode is by simple wedge analysis. We find that the simple wedge analysis is adequate for routine shoulder failures. For slope failures above the road however, defining the actual slip surface is required rather than the simple wedge analysis.

The user can input normal geotechnical strength parameters without a user input subgrade modulus. The WVDOH provides conservative presumptive strength parameters when laboratory results are unavailable. These presumptive values and assistance with the use of PSSLOPE can be obtained by contacting the Geotechnical Unit.

For pile walls, we generally require a long-term Factor of Safety (FS) of 1.3 and check the deflection in the service limit state (FS=1). The deflection is limited based on what is adjacent to the wall. If the wall is next to pavement, we limit the deflection to 1 inch. If the wall is at least 4 feet from the pavement, we limit it to 2 inches.

Both 4 and 6-foot spacings are allowed. Greater than 6-foot spacing is not allowed without a soil arching check to ensure ground is not lost between the piles beneath the lagging. When 6-foot spacing is used, we require the concrete to be placed to the bottom of the lagging to limit the gap between the piles. Based on 6-foot pile spacing, standard precast concrete lagging 6 inches thick can be used for walls that have up to 12 feet of exposed height. For walls on a 6-foot spacing and an exposed height of 12 to 18 feet, 8-inch thick standard precast concrete lagging should be used.

PSSLOPE may also be used to analyze the stabilizing effect of abutment piles for embankments 20 feet or less in height. For higher embankments, the FS of 1.5 must be based on the materials' strength properties and geometry without considering the stabilizing effect of the piles. For abutment piles, we limit the free-head deflection to 0.5 inches prior to constructing the bridge (service limit state). Also, the pile is checked for flexure by increasing the FS in the input to bring the overall initial and final FS to 1.5 (e.g., initial FS x input FS = 1.5). An additional check for the combined axial and flexure (e.g., in LPILE) in the strength limit state should be performed based on the maximum moment resulting from the FS of 1.5 obtained as discussed above.