2? That is, find the intersection point c between the equation straight line and the y axis, and the geometric relationship is 20√3.

3? According to the mechanics of materials, the normal stress with the maximum principal stress of 30 degrees is calculated, which is brought into the above Mohr-Coulomb equation, and the maximum shear stress that this surface can bear is calculated, and the existing shear stress on this surface is subtracted. (According to your understanding)

The horizontal and vertical coordinates of the tangent point between a straight line and a circle are.

5? That is, when the stress circle with the maximum principal stress of 0 is tangent to the straight line of the Mohr Coulomb equation, the other intersection point between the stress circle and the X axis seems to be =2c*cos internal friction angle /( 1+sin internal friction angle). Got it.

There are formulas in mine rock mechanics, which are actually based on this picture I sent. I'm just saying how.