For my research, it is necessary to find the width (in the figure, BE) of the failure wedge in Terzaghi, Vesic, or Prandtl bearing capacity theories for shallow foundations. I searched the literature but could not find any equations or calculations. I tried the trigonometric method, but the resulting value was too large compared to real-world observations. Does anyone know how to determine BE from the figure? Thanks!

N.B: in my calculation, I found BE= 1.26 m for 200mm diameter foundation.