Slope stability is the process of calculating and assessing how much stress a particular slope can manage before failing. Examples of common slopes include roads for commercial use, dams, excavated slopes, and soft rock trails in reservoirs, forests, and parks. Considering the importance of slope stability to their work, it’s beneficial for civil engineers to understand how to properly evaluate slope stability and leverage various techniques to achieve slope stabilization.

Evaluating Slope Stability

Civil engineers evaluate slope stability on the following premise: if a slope is stable enough to resist movement, then it is considered stable; whereas if the movement is too strong for a slope, then it is considered unstable. There are a number of elements that factor into determining slope stability and are analyzed through a series of tests by civil engineers. Four of the most prominent factors include:

• Relief – height differences amongst the slope’s terrain.
• Material Strength – the strength of the material used in creating the slope.
• Soil Water Content – relative amount of water in the soil surrounding the slope.
• Vegetation – plants and vegetation covering and/or surrounding the slope area.

Another factor which civil engineers must keep in mind is whether they are interested in determining short-term stability, long-term stability, or both. In either of these cases, civil engineers will need to evaluate the soil and determine if there is potential for slippage or sliding. In analyzing for long-term stability, engineers will also need to consider a number of factors, such as evaluating the potential quality of the soil in five or ten years or potential environmental events that could rupture or alter the soil.

Techniques for Stabilization

There are a number of techniques that civil engineers can leverage in achieving stabilization, some of which include:

• Anchor blocking – where blocks are strategically placed across the slope to resist the movement of sliding soil.
• Soil nailing – stabilization is achieved through the use of steel nails, which help provide support to the slope and/or infrastructure.
• Gabions – attempt to provide stability through the use of walls (similar to blocks) formed with the soil. These walls are capable of being temporary for stability rehabilitation or permanent.
• Micropile slide stabilization system – uses micropiles, concrete beams, and at times anchors to achieve stabilization. With this system, civil engineers insert a concrete beam into the ground then drill micropiles into the beam at various angles. Once complete, the connected micropiles will provide enough stability to protect an infrastructure from any sliding forces it may encounter.

One of the more recent trends in slope stability is the implementation of sustainable slopes, particularly for flood protection systems. This process has become quite complicated as a result of the numerous variables that come with introducing a new and powerful element such as water. Due to these variables, civil engineers have had to expand and tighten their assessment and calculation skills as they deal with new uncertainties, such as the exact strength and power of a given flood.

3D slope analysis is another growing trend for achieving and maintaining slope stability. Although not always necessary, 3D slope analysis has developed into a unique component of the slope stability process as it provides civil engineers with the capability to observe and analyze the actual state of the slope, as opposed to 2D which often relies upon assumptions to simplify the process. Furthermore, 2D slope analysis can be done only once a civil engineer knows the configuration and soil framework, whereas 3D slope analysis is able to manage more complex and potentially unknown factors. Examples of when 3D slope analysis may be used include:

• Slopes featuring complex geometry
• Differences in the geometry of slope and slip surface
• Locally surcharged slope

Slope stability has become a crucial component of America’s expanding infrastructure ecosystem. By calculating slope stability, civil engineers are able to create beautiful and innovative infrastructures in regions and areas that in the past were deemed unsafe for a building. Furthermore, the insight gained by determining slope stability has given civil engineers an expanded understanding of natural laws and forces, which they can study to improve future projects, as well as progress the civil engineering industry as a whole.