Abstract
Use of stone column technique to improve soft foundation soils under roadway embankments has proven to increase the bearing capacity and reduce the potential settlement. The potential contribution of stone columns to the stability of roadway embankments against general (i.e. deep-seated) failure needs to be thoroughly investigated. Therefore, a two-dimensional finite difference model implemented by FLAC/SLOPE 7.0 software, was employed in this study to assess the stability of a roadway embankment fill built on a soft soil deposit improved by stone column technique. The stability factor of safety was obtained numerically under both short-term and long-term conditions with the presence of water table. Two methods were adopted to convert the three-dimensional model into plane strain condition: column wall and equivalent improved ground methods. The effect of various parameters was studied to evaluate their influence on the factor of safety against embankment instability. For instance, the column diameter, columns’ spacing, soft soil properties for short-term and long-term conditions, and the height and friction angle of the embankment fill. The results of this study are developed in several design charts.
Highlights
The most common type of slope instability that is more likely to happen when constructing roadway embankments on soft soil deposits is the global or deep-seated failure
This may be attributed to the fact that the equivalent improved ground method provides continuous failure surface in such a way that every point located on that slip surface reached its shear strength at the same time unlike the column wall method where no continuous slip surface was observed and not all the points mobilized their shear strengths [14]
In order to assess the factor of safety against general deepseated failure for embankments constructed on granular column-improved ground with the presence of water table, a two-dimensional finite difference numerical analysis was performed using FLAC/SLOPE 7.0 software
Summary
The most common type of slope instability that is more likely to happen when constructing roadway embankments on soft soil deposits is the global or deep-seated failure. Finite Difference Method offers several advantages over Limit Equilibrium Method in computing the factors of Reference [1] investigated the stability of embankments supported by granular columns in the undrained (i.e. shortterm) condition by means of two methods of equivalency; column wall and equivalent improved ground methods. They recommended a reduction factor of 0.9 for the factor of safety obtained from the equivalent improved ground method if a water table is not considered and 0.92 if the water table is taken into consideration
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