Joint Plane FOS

Dear users,

will somebody help me. What Joint Plane FOS command (screenshot is attached) calculates by default?

Thanks in advance!


This is just the shear strength divided by the shear stress. So if (cohesion + tan(friction)*(normal force)) = 10 MPa and the shear stress is 5 MPa, the plot will show a value of 2. If the joint is sliding, the stress equals the strength, so it will show a value of 1.

If it’s failing in tension, it shows 0.

Thanks Jim!

Really appreciate the answer. Does it mean that in the case of cyclic loading cohesion and tension are unrecoverable? In other words, if joint is sliding or opening for the first time, cohesion and tension drops to zero and remain zero till the end of the calculation? By the way, is the Join Plane FOS reachable by Fish command?


Well, the joint plane FOS plot item doesn’t change anything. It is only used for plotting. You can get the FOS with FISH function block.subcontact.sratio.

For your second question, yes, by default the cohesion or tension will drop to 0 when the strength is exceeded. You can specify a residual cohesion or tension that is not 0 if you want. With the mohr model, the cohesion will never recover back to the initial value.

You can use the softening-healing mohr model (here) if you want the cohesion to recover when the joint stops sliding.