Given the initial effective stress state at a point within a soil mass (s_y=2.5 daN/cm2, s_x=1.5 daN/cm2, t_xy=t_xy=0.4 daN/cm2) and effective soil shear strength parameters at the same point (friction angle=30 degrees, cohesion=0.5 daN/cm2), find the maximum principal effective stress at failure assuming the minimum principal effective stress is kept constant at its initial value. Find also the directions of the two principal stresses at failure.
Note: Solve this problem plotting the Mohr's circle at scale and use the Pole method.