In order to develop an efficient slope stability method, it is important to know how the factor of safety, the phi-c ratio and other measures of a slope’s stability change with increasing slope height and angle. There are several factors which contribute to this, such as slope geometry, soil type and climatic conditions. These can all be optimized to enhance the safety of a cut slope.
The best method for achieving this is to use the limit equilibrium technique. This approach uses rigorous plasticity theory to analyze the interaction of a number of soil parameters and to determine the true factor of safety. It is a more rigorous approach than the more common FEM model. However, it is still in its early phases of application.
As the name implies, the factor of safety is the ratio between forces which resist movement and the forces which drive it. This value is inversely proportional to the slope’s angle. Therefore, decreasing the slope’s angle is a good way to increase its safety. When the slope’s height increases, the factor of safety also increases, but in a more gradual manner.
Another study in which the height and angle of a slope were systematically varied to determine their effect on the factor of safety is the Arba Minch-Chencha upgrading road project. Here, 24 dataset samples were collected from six different cut-slope sites. They were categorized into two groups – those before and those after saturation. Both sand and clayey soils were used.
For each site, a range of slope angles were used to compare the various methods. After determining which factors influenced the factors of safety, the slopes were modeled with three different analysis models. Each model is designed to take into account the type of soil, the slope height and the factor of safety. Using this information, the slope’s stability was analyzed using LEM and Plaxis 2D. Although the studies had limited statistical significance, they provided valuable information about the relationship between the factors of safety and the other relevant aspects of a cut slope.
Aside from the factors of safety, a more sophisticated technique of analyzing the stability of a cut slope is the limit analysis. Limit analysis is based on rigorous plasticity theory. This involves the use of a large data set to study the effect of varying soil height and angle on the factor of safety.
Compared to the LEM, the limit equilibrium technique is still in its early stages of implementation. One of the major benefits of this technique is that it provides a more rigorous approach to evaluating the relative merits of a number of slope stability measures.
Overall, the slope’s safety increased significantly when the angle and height of the slope were decreased. While the factors of safety increase with slope height, the slope’s failure surface may not. However, this should not discourage engineers from using the techniques.
While there is no single best method for maximizing the stability of a cut slope, understanding the relationship between the factors of safety and the slope’s angle and height is critical to developing an effective slope stability method.