---
title: "Define joint; classification and importance"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:define-joint-classification-and-importance"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/define-joint-classification-and-importance
site: BCT Engineering
---

# Define joint; classification and importance

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2074 Chaitra, 4 marks; 2074 Asoj, 3 marks; 2065 Shrawan (old course), 2+3+3 marks (asked 3 times)
- Video: [Joints in Engineering Geology | Hindi | Folds & Faults | Structural Geology |](https://www.youtube.com/watch?v=bdUTf-zO34I) — Civil Inside
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/define-joint-classification-and-importance
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Define joint. Describe the geometric classification of joints with their engineering importance.

## Short answer

A joint is a fracture with little to no displacement. Based on attitude to bedding, joints are strike, dip, oblique or bedding type. They weaken rock, cause slope failures, allow seepage and influence tunneling and quarrying.

## Answer

A **joint** is a fracture or crack in a rock along which there has been no (or negligible) displacement of the two sides.

#### Geometric classification of joints
Based on the relation of the joint with the attitude of the host rock (strike and dip of beds):
1. **Strike joints** - run parallel to the strike of the beds.
2. **Dip joints** - run parallel to the dip direction of the beds (at right angles to the strike).
3. **Oblique (diagonal) joints** - cross the bed at an angle to both strike and dip.
4. **Bedding joints** - lie along the bedding planes.

Based on the relation to folds, longitudinal, transverse and oblique joints are also distinguished. Joints that occur in parallel groups form a **joint set**, and two or more sets form a **joint system**.

```text
       strike joint   dip joint   oblique joint
     ----------------  |  |  |    /  /  /
     ----------------  |  |  |   /  /  /
     (parallel to      (along      (at an angle)
      strike)           dip)
```

#### Engineering importance
- **Reduce rock strength** and bearing capacity; blocks bounded by joints can slide or fall.
- **Slope stability**: joints dipping out of the slope or intersecting each other give wedge, plane and toppling failures.
- **Seepage**: joints are paths for ground water, causing dam leakage and tunnel inflow.
- **Weathering** starts along joints, so the rock deteriorates to a greater depth.
- **Quarrying**: joints help in extracting blocks, and close jointing reduces block size.
- **Tunnelling**: joint orientation controls overbreak and roof falls; the tunnel axis should be at a high angle to the strike of the joints.
- Grouting and rock bolting are needed in highly jointed rock.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A joint is a fracture with what displacement?
   A. None or negligible
   B. Large
   C. Kilometres
   D. Always vertical
   Answer: A. Fault has displacement. (Key point: Joint)

2. Strike joints run?
   A. Along dip
   B. Parallel to strike of beds
   C. Oblique
   D. Along bedding
   Answer: B. Dip joints along dip. (Key point: Strike joint)

3. Joints dipping out of slope cause?
   A. Stability
   B. Nothing
   C. Plane, wedge and toppling failures
   D. Cementation
   Answer: C. Sliding blocks. (Key point: Slope)

4. Tunnel axis relative to strike joints?
   A. Parallel
   B. Always along
   C. Irrelevant
   D. High angle to strike
   Answer: D. Reduces overbreak. (Key point: Tunnel)

## Related in Engineering Geology I

- [Engineering significance of joints](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-joints) — Engineering Geology I, chapter 5
- [Engineering significance of joint and fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-joint-and) — Engineering Geology I, chapter 5, asked 2×
- [What is joint; engineering significance of joint and fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Awhat-is-joint-engineering-significance) — Engineering Geology I, chapter 5, asked 2×
- [Genetic classification of fault and joint](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Agenetic-classification-of-fault-and) — Engineering Geology I, chapter 5
- [Fault versus joint](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afault-versus-joint) — Engineering Geology I, chapter 5, asked 2×
- [Fold, fault, joint, thrust in tunnelling](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afold-fault-joint-thrust-in) — Engineering Geology I, chapter 5

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- [Pipe joints; expansion joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-joints-expansion-joint) — Water Supply Engineering, chapter 8, asked 3×
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