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Preliminary evidence-based approach for forecasting cut slope deterioration, A
Werley, Keara D.
Werley, Keara D.
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2024
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Abstract
Constructed rock slopes may physically deteriorate over time, which can lead to increasing rockfall frequency. Physical deterioration leads to performance deterioration, which changes slope risk through time. Slope risk depends on the hazard level of the slope, as well as its potential impacts on the roadway and roadway users. Thus, forecasting physical slope deterioration and therefore slope performance deterioration is critical to the long-term decision making of transportation agencies. However, deterioration modeling of cut slopes is not yet well-established, and existing methods used for other types of geotechnical assets such as Markov models may not be well-suited for application to cut slopes. Therefore, this research proposes a new framework for physical deterioration modeling of cut slopes using conceptual models that predict how hazard components of the slope may change through time.
Conceptual models were developed for ditch effectiveness deterioration and rockfall frequency increases through time due to weathering since excavation of the cut slope, scaling, and rock bolting. The ditch effectiveness deterioration conceptual model was evaluated using 2D numerical modeling of rockfall trajectories and talus pile growth simulation. Numerical modeling results for steeper cut slopes agree with the conceptual model, but the conceptual model may be conservative for shallower cut slopes with angles less than 45 degrees. However, the conceptual model is parameterized in such a way that it can be adjusted for shallower cut slopes.
The time-since-excavation, scaling, and rock bolting conceptual models were evaluated using two datasets that represent slope performance and rockfall activity through time for mitigated and un-mitigated slopes. The results of these analyses are broadly consistent with the conceptual models and indicate that older cut slopes may have a constant level of rockfall hazard over time. Scaling and rock bolting often reduce rockfall frequency within a certain volume range.
Parameters were defined in mathematical relationships for each conceptual model. Detailed guidance is provided for parameter selection for the ditch effectiveness deterioration conceptual model. Some guidance is given for the time-since-excavation, scaling, and rock bolting conceptual models, although further guidance may be a topic of future research.
Lastly, forecasted changes in slope performance were compared between the conceptual models and hazard deterioration models used by the Colorado Department of Transportation (CDOT). In most cases, the CDOT models were found to overestimate physical slope deterioration compared to the proposed conceptual models.
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