Abstract
Slope failures in high plasticity clay deposits are common occurrences in many parts of the world. In western and central Alabama, expansive Prairie clays are commonly found, and shallow slope failures have occurred in both fill and cut slopes containing these high plasticity clays. The objective of this study was to examine the effects of suction and the use of nonlinear strength envelopes on the embankment stability of a section of highway AL-5. The testing program consisted of fifteen ring shear tests performed using a Bromhead Ring Shear Device. The results of the tests were used to develop both linear and nonlinear fully softened and residual strength envelopes. The saturated strength envelopes are then used in a limit equilibrium slope stability analysis with and without the effects of suction. The results show stability (factor of safety >1) for all cases except the residual friction angle without suction. Given these results, large slope failures are unlikely to occur in this area, but surficial failures and deformations due to creep may be possible. These results demonstrate the importance of considering the effects of suction and nonlinear strength envelopes when examining the potential for shallow slope failures in high plasticity clays.
Highlights
Shallow slope failures are a common occurrence in both fill and cut slopes in westernAlabama
No tests were performed at stresses below 20 kPa, so it is not known how well either envelope represents the strengths at very shallow depths
The saturated residual and fully softened strengths (Table 2) of the expansive Prairie clays underlying a portion of AL-5 have been characterized using torsional ring shear testing
Summary
The Alabama landslide database [1] found that almost USD 16 million was spent to repair slope failures in the Selma, Tuscaloosa and Midway Groups between 2005 and 2015. This figure only includes landslides for which federal emergency relief funds were requested, so the repair cost for all landslides in these units is likely much higher. It is believed that these failures can be partially explained through strength loss due to repeated cycles of wetting and drying in the high plasticity clays that are ubiquitous in these regions. Understanding the strength of these soils is critical to be able to design effective repairs and avoid repeated failures
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