---
title: "Seepage pressure"
subject: "Soil Mechanics"
chapter: 6
key: "semester_4/soil_mechanics:seepage-pressure-define"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/seepage-pressure-define
site: BCT Engineering
---

# Seepage pressure

Soil Mechanics · Chapter 6: Principle of Effective Stress, Capillarity and Permeability

- Asked in: 2078 Chaitra, 1 marks
- Video: [Concept of Seepage Pressure in Soil | Soil Mechanics for GATE & ESE  | Civil Engineering](https://www.youtube.com/watch?v=k952tMoFA4U) — CIVIL ACADEMIA
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/seepage-pressure-define
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-6

## Question

Define seepage pressure.

## Short answer

Seepage pressure is the pressure exerted by flowing water on soil grains in the direction of flow, equal to h times gamma_w or i times gamma_w times L. Upward seepage pressure reduces effective stress; downward flow increases it.

## Answer

**Seepage pressure** is the pressure (force per unit area) exerted by water flowing through the soil on the soil grains in the direction of flow. For a hydraulic head loss $h$ over a length $L$, the seepage force per unit volume of soil is $j = i\gamma_w$, and the seepage pressure over the length $L$ is

$$
p_s = h\,\gamma_w = i\,\gamma_w L
$$

It acts upward in upward flow and reduces effective stress; it acts downward in downward flow and increases it.

## Check yourself

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

1. Seepage pressure is:
   A. Pressure of static water at depth
   B. Pressure exerted by flowing water on soil grains in the direction of flow
   C. Pressure due to capillary suction
   D. Pressure from the weight of the soil
   Answer: B. It is the drag of flowing water on grains, acting in the flow direction. (Key point: Meaning)

2. For head loss h over length L, seepage pressure is:
   A. p_s = h gamma_w = i gamma_w L
   B. p_s = i gamma_w
   C. p_s = gamma' L
   D. p_s = h/L
   Answer: A. p_s = h gamma_w = i gamma_w L; the force per unit volume is j = i gamma_w. (Key point: Formula)

3. Seepage pressure in upward flow:
   A. Increases effective stress
   B. Has no effect
   C. Reduces effective stress
   D. Doubles total stress
   Answer: C. Upward seepage acts against gravity and reduces effective stress; downward flow increases it. (Key point: Effect on effective stress)

## Related in Soil Mechanics

- [Upward seepage stress variation diagram](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aupward-seepage-stress-diagram) — Soil Mechanics, chapter 7