Geotechnical Engineering Online Library

A 30-m long railroad embankment failure that occurred on May 25 2011 in the city of Ann Arbor, Michigan, is presented. Emphasis is given on the field observations of the failure, the characterization of the site conditions and the seepage and slope stability analyses, all of which represent important components of the training and practice of a geotechnical engineer. The failure occurred following a record wet season that resulted in ponding water against the embankment and high enough water pressures and exit gradients that resulted in instability of the railroad embankment. Detailed background material and the methodology for using the case history in geotechnical engineering education are presented.

The objective of the paper is the presentation of a case study developed for geotechnical engineering instruction. The examined case study is suitable for undergraduate instruction and refers to the geotechnical design of a railway embankment focusing on slope stability analyses and settlement calculations. The presented geotechnical data have resulted from the geotechnical study implemented by Edafomichaniki S.A. within the framework of the project “Geotechnical Design of the New Railway Alignment between the Existing Line and Kavala’s Port”. The geotechnical design of a railway embankment is described thoroughly in the current paper and includes the following: a) the evaluation of the available geotechnical data encompassing the determination of soil stratigraphy and geotechnical design parameters of the encountered formations, b) the performance of geotechnical calculations regarding slope stability analyses and settlement calculations with detailed reference to consolidation theory and c) the presentation of the construction methodology of the embankment. The usefulness of the examined case study is highlighted through the achievement of a significant number of learning outcomes. The current paper is accompanied with detailed supplementary material.

The 1981 upstream slope failure in San Luis Dam in California, USA, is analyzed for stability and deformations in two- and three-dimensions using continuum-mechanics-based analysis procedures implemented in the computer programs FLAC and FLAC3D. The analysis results (failure surface, factor of safety, and displacements) from the continuum models are in general agreement with the field data. In addition, two-dimensional slope stability analysis results using a modified form of limit-equilibrium-based Spencer’s procedure for variable factor of safety implemented in the computer program SSTAB2 are included. Overall, the analysis results supplement the previously reported failure analyses. The paper serves three primary functions: (1) it documents results of a different analysis of the 1981 San Luis Dam slope failure; (2) it demonstrates the use of 2-D and 3-D continuum models to study the onset of instability, failure surface geometry and location, and permanent displacements associated with slope failures; and (3) it demonstrates the use of variable factor of safety to identify location of instability initiation, and progression of instability in a soil deposit. In addition, the paper demonstrates the benefits of three-dimensional analysis for complex conditions in dam engineering practice.