A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Level Two (Advanced FAQs)
Part I: Design of Foundation
1. What are the components in contributing the bearing capacity of
shallow foundation? (FD1)
Based on Terzaghi’s bearing capacity equation, there are three
components in contribution to the bearing capacity:
(i) Surcharge pressure
Foundations are normally not placed directly on the ground level.
Instead, they are installed at a depth below the existing ground level.
The soil pressure arising from the depth of soils serves as a
surcharge imposing a uniform pressure at foundation level.
(ii) Self-weight of soils
The self-weight of soils contribute to the bearing capacity and is
represented by 0.5rBNr (r=density of soils).
(iii) Shear strength
The shear strength of soils contributes to the bearing capacity and is
represented by cNc.
2. What is the difference between pad foundation, strip foundation
and raft foundation? (FD2)
Shallow foundation is commonly accepted as foundation with founding
level less than 3m from ground surface. In case surface loads or surface
conditions could still affect the bearing capacity, the foundation which sits
on it is called shallow foundation.
Pad foundation refers to the foundation which is intended for sustaining
concentrated loads from a single point load such as structural columns.
Strip foundation is used to support a line of loads such as load-bearing
walls. For instance, closely-spaced columns render the use of pad
foundation inappropriate and strip foundation may be a better alternative.
Raft foundation consists of a concrete slab which extends over the entire
loaded area so that loads from entire structure are spread over a large area
leading to a reduction of the stress of foundation soils is reduced. Moreover,
raft foundation serves to avoid differential settlement which otherwise
would occur if pad or strip foundation is adopted.
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