The image above represents mohr – coulomb criterion.

To compute for mohr – coulomb criterion, three essential parameters are needed and these parameters are **Cohesion (|τ _{o}), Co-efficient of Friction (μ) **and

**Normal Stress (σ**

_{n}).The formula for calculating the mohr – coulomb criterion:

|τ| = τ_{o} + μσ_{n}

Where;

|τ = Mohr – Coulomb Criterion

|τ_{o} = Cohesion

μ = Co-efficient of Friction

σ_{n} = Normal Stress

Let’s solve an example;

Find the mohr – coulomb criterion when the cohesion is 7, the co-efficient of friction is 30 and the normal stress is 28.

This implies that;

|τ_{o} = Cohesion = 7

μ = Co-efficient of Friction = 30

σ_{n} = Normal Stress = 28

|τ| = τ_{o} + μσ_{n}

|τ| = 7 + 30(28)

|τ| = 7 + 840

|τ| = 847

Therefore, the **mohr – coulomb criterion **is **847.**

**Calculating the Cohesion when the Mohr – Coulomb Criterion, the Co-efficient of Friction and the Normal Stress is Given.**

|τ_{o} = |τ| – μσ_{n}

Where;

|τ_{o} = Cohesion

|τ = Mohr – Coulomb Criterion

μ = Co-efficient of Friction

σ_{n} = Normal Stress

Let’s solve an example;

Find the cohesion when the mohr – coulomb criterion is 44, the co-efficient of friction is 10 and the normal stress is 4.

This implies that;

|τ = Mohr – Coulomb Criterion = 44

μ = Co-efficient of Friction = 10

σ_{n} = Normal Stress = 4

|τ_{o} = |τ| – μσ_{n}

|τ_{o} = 44 – 10(4)

|τ_{o} = 44 – 40

|τ_{o} = 4

Therefore, the **cohesion **is **4.**

**Calculating the Co-efficient of Friction when the Mohr – Coulomb Criterion, the Cohesion and the Normal Stress is Given.**

μ = ^{|τ| – |τo} / _{σn}

Where;

μ = Co-efficient of Friction

|τ = Mohr – Coulomb Criterion

|τ_{o} = Cohesion

σ_{n} = Normal Stress

Let’s solve an example;

Find the co-efficient of friction when the cohesion is 10, the mohr – coulomb criterion is 24 and the normal stress is 12.

This implies that;

|τ = Mohr – Coulomb Criterion = 24

|τ_{o} = Cohesion = 10

σ_{n} = Normal Stress = 12

μ = ^{|τ| – |τo} / _{σn}

μ = ^{24 – 10} / _{12}

μ = ^{14} / _{12}

μ = 1.667

Therefore, the **co-efficient of friction **is **1.667.**

**Calculating the Normal Stress when the Mohr – Coulomb Criterion, the Co-efficient of Friction and the Cohesion is Given.**

σ_{n} = ^{|τ| – |τo} / _{μ}

Where;

σ_{n} = Normal Stress

|τ = Mohr – Coulomb Criterion

|τ_{o} = Cohesion

μ = Co-efficient of Friction

Let’s solve an example;

Find the normal stress when the mohr – coulomb criterion is 30, the cohesion is 14 and the co-efficient of friction is 5.

This implies that;

|τ = Mohr – Coulomb Criterion = 30

|τ_{o} = Cohesion = 14

μ = Co-efficient of Friction = 5

σ_{n} = ^{|τ| – |τo} / _{μ}

σ_{n} = ^{30 – 14} / _{5}

σ_{n} = ^{16} / _{5}

σ_{n} = 3.2

Therefore, the **normal stress **is **3.2.**

Nickzom Calculator – **The Calculator Encyclopedia** is capable of calculating the mohr – coulomb criterion.

To get the answer and workings of the mohr – coulomb criterion using the **Nickzom Calculator – The Calculator Encyclopedia. **First, you need to obtain the app.

You can get this app via any of these means:

**Web** – https://www.nickzom.org/calculator-plus

To get access to the **professional **version via web, you need to **register** and **subscribe **for** NGN 1,500 **per** annum** to have utter access to all functionalities.

You can also try the **demo **version via https://www.nickzom.org/calculator

**Android (Paid)** – https://play.google.com/store/apps/details?id=org.nickzom.nickzomcalculator

**Android (Free)** – https://play.google.com/store/apps/details?id=com.nickzom.nickzomcalculator

**Apple (Paid)** – https://itunes.apple.com/us/app/nickzom-calculator/id1331162702?mt=8

Once, you have obtained the calculator encyclopedia app, proceed to the **Calculator Map, **then click on **Geology**** **under **Add-on.**

Now, Click on **Rock Mechanics**** **under **Geology**

Now, Click on **Mohr – Coulomb Criterion** under **Rock Mechanics**

The screenshot below displays the page or activity to enter your values, to get the answer for the mohr – coulomb criterion according to the respective parameters which are the **Cohesion (|τ _{o}), Co-efficient of Friction (μ) **and

**Normal Stress (σ**

_{n}).Now, enter the values appropriately and accordingly for the parameters as required by the **Cohesion (|τ _{o})** is

**7**,

**Co-efficient of Friction (μ)**is

**30**and

**Normal Stress (σ**is

_{n})**28**

**.**

Finally, Click on Calculate

As you can see from the screenshot above, **Nickzom Calculator**– The Calculator Encyclopedia solves for the mohr – coulomb criterion and presents the formula, workings and steps too.