What safety factor (SF) value indicates a stable slope?

A safety factor (SF) is a crucial element in assessing slope stability in geological contexts. The safety factor is determined by comparing the resisting forces that prevent a slope from failing to the driving forces that tend to cause a slope failure. When the safety factor is greater than one, it indicates that the resisting forces are greater than the driving forces, thus suggesting that the slope is stable and has a margin of safety against failure.

When the safety factor is exactly equal to one, it means that the resisting forces and driving forces are in balance, which means that any slight change in conditions—such as increased water content or structural changes—could lead to failure. Therefore, a safety factor greater than one not only indicates stability but also provides assurance that the slope can withstand some variations in conditions without failing.

Furthermore, a safety factor greater than two is often considered very safe, but the critical threshold for indicating stability begins at a safety factor greater than one. This threshold is key for engineers and geologists in the field to determine whether a slope can be relied upon to remain intact under current environmental conditions.