Software Discussion-PPT Presentation

PPT Presentation

Pdf Summary

The 2021 DFI S3 software discussion examined slope stability at Station 459800, where a new railroad track was proposed between existing tracks and the Missouri River. Participants analyzed rapid drawdown from elevation 510 to 498 feet over 14 days, using the published H-pile arrangement and resistance. The task was to identify concerns, not design alternatives.<br /><br />Presentations compared limit-equilibrium (LEM) and finite-element (FEM) methods, 2D and 3D analyses, pile representations, groundwater assumptions, and circular versus non-circular slip searches. In the Rocscience analysis, supported high-water factors of safety were 1.36–1.39, below the 1.5 target. Rapid-drawdown results were 1.14–1.17, also below the 1.2 target. The presenters emphasized that coupled pile analysis can account for spacing, batter, and allowable soil displacement.<br /><br />Other analyses highlighted sensitivity to assumptions and methods. Gregory reported that FEM-derived pore-water pressures and refined non-circular searches produced more realistic, and sometimes lower, safety factors than simplified approaches; simplified 3D analysis yielded an approximately 8% higher factor than 2D. Bentley reported a Duncan three-stage rapid-drawdown factor of safety of 1.14 with piles, compared with 0.83 for transient LEM/FEM seepage analysis. Fully coupled FEM predicted failure below a factor of safety of 1, including failure about 10.5 days after drawdown in a two-pile case.<br /><br />The discussion concluded that software implementation, analysis method, search strategy, groundwater modeling, pile representation, and dimensionality can materially affect results. Non-circular searches may reveal more critical mechanisms, and transient seepage analysis can give substantially lower rapid-drawdown safety factors than simplified procedures. These differences warrant careful review and further investigation rather than reliance on a single analysis result.

Keywords

slope stability

rapid drawdown

Station 459800

limit equilibrium method

finite element method

pile analysis

groundwater modeling

factor of safety

non-circular slip surface

transient seepage