The stability of the slope is the potential of the slopes covered with soil to resist and undergo movements. Stability is determined by the balance between shear and shear strength. A previously stable slope may be initially affected by preparatory factors, making the slope conditionally unstable. The triggers of a slope failure may be climatic events that can then make an actively unstable slope, resulting in mass movements. Mass movements can be caused by increased shear stress, such as load, lateral pressure and transient forces. Alternatively, the shear strength can be decreased by weathering, changes in pore water pressure and organic material.
The field of slope stability encompasses the static and dynamic stability of slopes of land and rock dams, slopes of other types of slopes, excavated slopes and natural slopes in the soil and soft rocks. Research on gradient stability, analysis (including modeling) and design mitigation is often completed by geologists, geological engineers or geotechnical engineers. Engineering geologists and geologists can also use their knowledge about the land process and their ability to interpret surface geomorphology to determine relative slope stability based simply on site observations.
If the forces available to resist movement are greater than the forces driving the movement, the slope is considered stable. A safety factor is calculated by dividing the forces resisting the movement by the forces driving the movement. In earthquake-prone areas, the analysis is usually performed for static conditions and pseudo-static conditions, where the seismic forces of an earthquake are assumed to add static charges to the analysis.