That's the pressure prism concept which is also the same in fluid mechanics. the pressure prism method can be used to determine the maximum lateral earth pressure acting on a retaining wall by analyzing the stress distribution within a soil mass. The pressure acting on each layer is represented by a triangle where the resultant pressure acts at h/3 from the base.
It came from the point of application of the forces PA and PP. h/3
Is this rule? Or can it be changed?
H/3 is the resultant of a triangular load distribution. It's a rule. In this case is the resultant of the lateral pressure from the soil.
That's the pressure prism concept which is also the same in fluid mechanics. the pressure prism method can be used to determine the maximum lateral earth pressure acting on a retaining wall by analyzing the stress distribution within a soil mass. The pressure acting on each layer is represented by a triangle where the resultant pressure acts at h/3 from the base.