---
title: "Define discontinuity"
subject: "Engineering Geology II"
chapter: 2
key: "semester_4/engineering_geology_ii:define-discontinuity"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/define-discontinuity
site: BCT Engineering
---

# Define discontinuity

Engineering Geology II · Chapter 2: Engineering Geology in Himalayas

- Asked in: 2075 Bhadra, 1 marks; 2073 Bhadra, 1 marks; 2071 Magh, 1 marks; 2079 Jestha, 2 marks (asked 4 times)
- Video: [Types of Discontinuities in the Rocks - Structural Geology and Stratigraphy - Engineering Geology](https://www.youtube.com/watch?v=cM1oWyqek8Q) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/define-discontinuity
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-2

## Question

Define discontinuity.

## Short answer

A discontinuity is a plane of weakness in a rock mass with negligible tensile strength, such as joints, faults, bedding, or foliation. It reduces rock mass strength, increases permeability, and controls slope and tunnel stability.

## Answer

A **discontinuity** is any plane or surface of separation in a rock mass across which the rock has negligible tensile strength and which interrupts the physical continuity of the rock. It is a general term covering bedding planes, joints, foliation, cleavage, faults, shear zones and thrusts.

- Discontinuities make a rock mass weaker, more permeable and more deformable than intact rock.
- Their orientation, spacing, persistence, roughness, aperture and filling control slope stability, tunnel behaviour, seepage and foundation safety.
- In the Nepal Himalaya, the major regional discontinuities are the MFT, MBT, MCT and STDS.

## Check yourself

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

1. What property characterises a discontinuity?
   A. Negligible tensile strength and interruption of rock continuity
   B. Very high tensile strength
   C. Being a mineral
   D. Being a soil layer
   Answer: A. A discontinuity is a surface of separation with negligible tensile strength. (Key point: Definition)

2. Which is NOT a discontinuity?
   A. Joint
   B. Fault
   C. Bedding plane
   D. Intact fresh quartz crystal grain interior
   Answer: D. Joints, faults, bedding, foliation and thrusts are discontinuities; intact rock is not. (Key point: Examples)

3. How do discontinuities change a rock mass compared with intact rock?
   A. Stronger and less permeable
   B. Weaker, more permeable and more deformable
   C. Unchanged
   D. Only colour changes
   Answer: B. They make the mass weaker, more permeable and more deformable. (Key point: Effect)