---
title: "What is stress path"
subject: "Soil Mechanics"
chapter: 10
key: "semester_4/soil_mechanics:stress-path-define"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/stress-path-define
site: BCT Engineering
---

# What is stress path

Soil Mechanics · Chapter 10: Shear Strength of Soil

- Asked in: 2075 Baisakh, 1 marks
- Video: [Stress Path And Types Of Mohr Failure Envelope | Shear Strength Of Soil | Soil Mechanics](https://www.youtube.com/watch?v=GlD8aRN3-BY) — Chaityendra Singh
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/stress-path-define
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-10

## Question

What is stress path?

## Short answer

Stress path is the locus of successive stress states of a soil element during loading, plotted on a p-q diagram. It shows stress changes from initial to failure, avoiding drawing multiple Mohr circles. Effective and total stress paths differ by pore pressure.

## Answer

A **stress path** is the locus of successive stress states of a soil element during loading, plotted as a line on a stress diagram. It shows how stress changes from the initial state to failure.

It is usually plotted in $p$-$q$ space, where $p = \frac{\sigma_1+\sigma_3}{2}$ and $q = \frac{\sigma_1-\sigma_3}{2}$, with the $K_f$ line (failure line) $q = p\sin\phi + c\cos\phi$. Each point represents a Mohr circle, so stress paths avoid drawing many circles. Total and effective stress paths differ by the pore pressure.

## Check yourself

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

1. What is a stress path?
   A. The path water takes through the soil
   B. The locus of successive stress states of a soil element from the initial state to failure
   C. A single Mohr circle at failure
   D. The line of maximum shear stress in a sample
   Answer: B. A stress path traces how stress changes during loading, shown as a line on a stress diagram. (Key point: Definition)

2. In p-q space, how are p and q defined?
   A. p = (sigma_1 + sigma_3)/2 and q = (sigma_1 - sigma_3)/2
   B. p = (sigma_1 - sigma_3)/2 and q = (sigma_1 + sigma_3)/2
   C. p = sigma_1 and q = sigma_3
   D. p = sigma_1 - sigma_3 and q = u
   Answer: A. p is the centre and q the radius of the Mohr circle. (Key point: p and q)

3. Why are stress paths convenient, and how do total and effective paths differ?
   A. They give the pore pressure directly without any tests; the paths are identical
   B. They apply only to drained tests; the paths differ by cell pressure
   C. They replace the failure envelope; the paths differ by sigma_3
   D. Each point stands for a Mohr circle so many circles need not be drawn; the paths differ by the pore pressure
   Answer: D. A point on the path represents a whole circle, and effective stress path is shifted from the total by u. (Key point: Advantage and total vs effective)