In soil mechanics, when a retaining structure remains stationary, what is the ratio of effective horizontal stress to effective vertical stress known as?

The ratio of effective horizontal stress to effective vertical stress when a retaining structure is stationary is known as K0, or the at-rest earth pressure coefficient. This coefficient describes the condition of the soil when it is not experiencing any lateral movement or additional forces that would affect its stress state.

In the context of soil mechanics, K0 can be understood as the ratio of the horizontal stress (σh) to the vertical stress (σv) within the soil mass in a state of rest, where the soil maintains its natural state without any disturbance that might lead to shearing or lateral movement.

K0 is particularly important in analyzing the stability of retaining walls and the pressures exerted on these structures under various loading conditions. The value of K0 is typically derived from the properties of the soil, most notably its angle of internal friction, and represents the way in which soil stresses interact when no lateral expansions or contractions are permitted.

Understanding K0 allows engineers to design retaining structures that account for the earth pressures in a more realistic manner, ensuring the stability and safety of the structure.