---
title: "Assumptions of conventional mat analysis"
subject: "Foundation Engineering"
chapter: 7
key: "semester_5/foundation_engineering:mat-assumptions-conventional"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/mat-assumptions-conventional
site: BCT Engineering
---

# Assumptions of conventional mat analysis

Foundation Engineering · Chapter 7: Mat Foundations

- Asked in: 2080 Baisakh, 2 marks
- Video: [Analysis and Design of Mat/Raft Foundation | Conventional Method | Foundation Engineering](https://www.youtube.com/watch?v=3PWamMNS5EE) — Sudip Dhakal
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/mat-assumptions-conventional
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-7

## Question

What are the basic assumptions in the conventional method of analysis of mat foundation?

## Short answer

Conventional method assumes mat is perfectly rigid, soil pressure distribution is linear (planar), centroid of pressure coincides with resultant of loads, mat divided into independent strips with no shear transfer, and column loads/spacing vary little.

## Answer

The basic assumptions of the conventional (rigid) method of mat analysis are:

1. The mat is **perfectly rigid** compared with the soil, so it settles as a plane (rigid body) and does not bend appreciably.
2. The **soil pressure is linear** (planar), given by $q = \dfrac{Q}{A} \pm \dfrac{M_xy}{I_x} \pm \dfrac{M_yx}{I_y}$.
3. The **centroid of soil pressure** coincides with the line of action of the resultant of the column loads (static equilibrium).
4. The mat is divided into **independent strips**, with no shear transfer between adjacent strips.
5. The soil is homogeneous, and column spacing and loads vary little (not more than about 20%), and spacing is less than $1.75/\lambda$.

## Check yourself

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

1. In the conventional method the mat is assumed to be:
   A. Flexible, bending with the soil
   B. Perfectly rigid relative to the soil
   C. Supported on springs of varying stiffness
   D. Hinged at every column
   Answer: B. The mat is rigid, so it settles as a plane and soil pressure is linear. (Key point: Rigid mat)

2. What soil pressure distribution is assumed?
   A. Parabolic
   B. Concentrated under columns only
   C. Linear (planar), q = Q/A +/- Mx y/Ix +/- My x/Iy
   D. Uniform irrespective of eccentricity
   Answer: C. A rigid mat gives a planar pressure from the combined axial and bending formula. (Key point: Soil pressure form)

3. What must coincide for static equilibrium?
   A. Centroid of soil pressure and line of action of the resultant column load
   B. Centre of mat and the heaviest column
   C. Mat edge and the water table
   D. Column spacing and mat thickness
   Answer: A. The centroid of soil pressure is taken to coincide with the resultant of the column loads. (Key point: Equilibrium)

4. How is the mat treated when analysing strips?
   A. Strips carry shear to each other
   B. Independent strips with no shear transfer between them
   C. One single beam
   D. As a circular plate
   Answer: B. The mat is divided into independent strips and shear between adjacent strips is neglected. (Key point: Strip independence)

## Related in Foundation Engineering

- [Conventional design of mat foundation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-conventional-design) — Foundation Engineering, chapter 7, asked 3×
- [Compensated foundation and types of mat](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Acompensated-foundation-mat-types) — Foundation Engineering, chapter 7, asked 7×
- [Why design a mat foundation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Awhy-design-mat) — Foundation Engineering, chapter 7
- [Mat bearing capacity: cohesive vs cohesionless](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-bc-cohesive-vs-cohesionless) — Foundation Engineering, chapter 7, asked 2×
- [Mat 18 m × 22 m, safe building weight](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-18x22-clay-ucs75) — Foundation Engineering, chapter 7, asked 2×
- [Soil pressure under rigid mat with column loads](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-rigid-soil-pressure-columns) — Foundation Engineering, chapter 7

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- [Two basic approaches of structural analysis](https://www.bctengineer.com/question.md?key=semester_4%2Ftheory_of_structures_i%3Atwo-basic-approaches) — Theory of Structures I, chapter 1, asked 3×