MohrPlotter v$\mathrm{.}3.10$ by Rick Allmendinger

A simple program can calculate the shear and normal stresses acting on a plane, determine the pore pressure necessary for rocks to fail. MohrPlotter is simple to use. You have received a manual as a handout. Please read the introduction, the entries to Failure by$....$ and Reactivation angles in the Calculation Menu chapter $($pages $5$ and $6).$ It is installed on the computers in the Computer lab $($REIC $316)$ and can also be downloaded for free:

wuw.rickallmendinger.net$/$mohrplotter$.$

Problem $1\mathrm{.}7$:

Enter the following initial values:

Stresses: $1=157,3=45$; leave $2$ blank

Failure Envelopes: Tensile Strength $=-10,$ Internal Angle of Friction $=35$; Cohesion is automatically determined

Leave Pre$-$existing fractures and Poles to Planes blank

In the top menu, go to Plot $->$ Show Construction Lines

In the menu, go to the Calculate tab and then Failure by and select

Increase P$($fluid$)$

What is the value of pore fluid pressure added $($round to the first decimal place$)?31\mathrm{.}9$

What are the shear $()$ and normal $($on$)$ stresses acting on the fracture $($indicated by red dot on the failure envelope$)?$ Look for the box at the bottom right or move the curser over the point and read the value from the lower left corner

What is the angle $$ that the pole of the shear fracture makes with $1?$

What is the actual angle the shear fracture makes with $01?+24,98-54\mathrm{.}94$

Reset the P$($fluid$)$ to $0$ and select the next failure method $($Failure by$...)$

Increase $01$

What is the value of $1$ necessary for failure?

What is the new differential stress $(1-3)?$

What are the shear $(r)$ and normal $(n)$ stresses acting on the fracture $($indicated by red dot on the failure envelope$)?$

What is the $$ angle with $1?$ Is it different from the Increasing P$($fluid$)$ failure? Why?

Reset $1$ to the initial value and select the next failure method

Decrease $3$

What is the value of $3$ necessary for failure?

What is the new differential stress $(1-3)?$

What are the shear $(T)$ and normal $(n)$ stresses acting on the fracture $($indicated by red dot on the failure envelope$)?$

What is the $$ angle with $1?$ Is it different from the Increasing P$($fluid$)$ failure? Why?

Problem $1\mathrm{.}8$:

Use the same initial values as in the previous problem, but enter a value of $30$ for Angle Static friction in the Preexisting fractures box. In the menu, go to Calculate Reactivation angles to find out what is the range of existing fractures with respect to $1?($Plot $>$ Reactivation angles

At what Angle Static friction do you get the narrowest range of pre$-$existing fractures?