Foundation engineering, also known as geotechnical engineering, applies theoretical knowledge concerning the behavior of soils and rocks and the construction of load-bearing structures to the planning and construction of foundations for infrastructure. At the most basic level, a foundation engineer would consider the kind of soil on which construction is to begin, allowing for the selection of the best material for the job, taking into account variables such as the manner in which such materials would need to be reinforced. This field of engineering not only establishes the physical qualities and quantities needed for the construction of foundations but establishes the necessary design parameters needed for such construction. Such parameters are established by evaluating factors such as the bearing capacity of a particular soil, allowable soil pressure, and the influence of slopes and adjacent foundations, among others.
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Foundation Engineering is critical in construction
An equally important facet of foundation engineering entails the maintenance and evaluation
of existing foundations, which in practice involves pre-empting the degradation or failure of a
foundation, and in some cases assessing the damage that has already occurred. Such risk assessments
require the foundation engineer to take into account factors such as the arrangement of physical
features, or topography, of the area being assessed, seismic forces, and groundwater, all of which
may play a part in the deterioration of existing foundations. This aspect of foundation engineering
is particularly important in minimizing risks to human safety which may occur as a result of unsound
foundations. Extrapolating along the lines of risk assessment, site conditions which may have
otherwise limited development potential may be mitigated through the improvement of the
engineering properties of the soil and rock foundations in themselves.
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Simply described, the foundation of a structure serves to transmit loads from the structure to the
earth. As such, the design of a foundation requires an estimation of the magnitude and location
of loads that need supporting, a plan for the evaluation of the subsurface, and the establishment
of the required soil parameters through field testing. Once these factors have been taken into
consideration, the foundation is designed such that construction is achieved in the most economic
manner feasible, while also ensuring that any risks which may be present during, or subsequent to
the construction of the foundation, are minimized.
Soil is key!
The most significant factors to be taken into consideration when designing foundations include
those concerning settlement and bearing capacity. Settlement takes into account the tendency
for soils to undergo consolidation, a process whereby soils decrease in volume over time under
permanent loads – in the case of foundation engineering, the weight of the structure and
the foundation itself. This process occurs due to the expulsion of water from soil without any
concomitant replacement with water or air, resulting therefore in an overall decrease in the volume
of soil. This was probably, at least, one of the variables the designers of the Tower of Pisa neglected to
consider, which eventually resulted in the distinctive tilt which gives the Tower its more recognizable
label as the Leaning Tower of Pisa.
Bearing capacity refers to the property of soil to support forces applied to the ground. Strictly
defined, the bearing capacity of soil would refer to the maximum contact pressure, averaged over
time, between the foundation and the soil, which would not produce shear failure in the soil – which
itself is related to the shear strength of the soil. This variable, in turn, is determined by the friction
and interlocking between soil particles.
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What we've learned so far
The history of foundation engineering may be traced as far back as Ancient Greece. As cities
grew larger in parallel with the progress of those ancient civilizations, buildings were erected on
foundations which were specifically constructed to serve as supporting structures. Until the 18th
century, however, no formalized discipline concerning the theoretical underpinnings of soil design
existed, and construction proceeded based on past experience rather than any demonstrable
protocol. The lack of anything resembling a scientific approach to the matter of foundation
engineering soon manifested itself in such famous engineering problems as the Leaning Tower
of Pisa, itself the result of an inadequate foundation on soil too soft on one side to completely
support the weight of the tower. These problems soon prompted scientists to begin examining the
subsurface in a more systematic fashion, resulting in the progression of foundation engineering from
century through to 1925, when modern geotechnical engineering is said to have begun,
the 18th
with the publication of Erdbaumechanick (Soil Mechanics) by the father of soil mechanics, Karl von
Terzaghi.
Historically, foundations simply consisted of buildings or structures being built in contact with the
ground, or otherwise in a manner known as ‘post in ground’ construction. Post in ground, also
known as earthfast construction, simply consisted of vertical roof-bearing posts being placed into
excavated post holes, and has been in use from the Neolithic period to the present. Structures
utilizing such construction methods are relatively impermanent but are simply to erect. Padstones
are another type of foundation which has been in use since Ancient Greece, and is simply single
stones which both spread the weight of a structure on the ground as well as elevating the structure.
Such elevation was of particular use in preventing the contents of granaries from vermin as well as
water seepage.
Dig deep?
Spread footing foundations, a type of shallow foundation, are typically used in residential buildings,
and consists of a wider lower portion which supports the load-bearing foundation walls, such as
to distribute the weight of the building over a greater area for increased stability. The design and
implementation of spread footings is influenced by soil factors, as well as the weight of the structure
that is being supported – this said, it could be argued that the design of nearly any foundation which
is placed, shallow or deep, would have to take into account these two factors. Spread footings may
be adapted to use in sites where gradients exist by being constructed as a series of steps cut into
the gradient. Such use of a spread footing is called a stepped footing. Another example of shallow foundation previously mentioned is the slab-on-grade foundation, also known as floating slab
foundations. These foundations are constructed by allowing a concrete slab to set within a mold
that is set into the ground; this concrete slab then serves as the foundation. The advantages of this
type of foundation are that it is cost-effective and relatively sturdy, however these points have to be
balanced against the fact that such a foundation restricts underground access to utility lines and can
result in significant heat loss when ground temperatures fall lower than that of indoor temperatures.
This second drawback may be mitigated however, by the use of insulation or heating systems,
although these solutions may entail additional costs/issues in themselves.
Deep foundations may be recommended over shallow foundations for a number of reasons, but
these reasons most commonly tend to be due to exceedingly large structural loads, such as those
that would be present in the construction of high rise buildings, poor quality soil at superficial
depths, or a lack of space for a sufficiently large shallow foundation to be able to support a
structure properly. As mentioned above, deep foundations may be classified according to the type
of foundation itself, the method by which the foundation is placed (also related to the type of
foundation) as well as the material the foundation is constructed from. Common materials used
as deep foundations include reinforced concrete, prestressed concrete, timber and steel. Deep
foundations which are driven into the ground are typically done so using a pile driver, a machine
which operates by alternatingly raising and releasing a weight onto a pile until it has reached the
required depth.
Piles give support
A particular advantages associated with driven piles are that the soil which is
displaced during the pile-driving process becomes compressed, effectively, acting as a splint, and
thereby increasing the load-bearing capacity of the pile. Furthermore, driven piles are considered
to have been ‘evaluated’ for their weight bearing ability, as the weight required to drive the pile
into the ground must necessarily exceed that of the structure which the pile is supporting, therefore
offering a considerable degree of certainty that the pile will be able to serve its function. Drilled
piles make use of the largest diameter piles, and permit pile placement even in dense subsurface
soil or rock. Examples of drilled piles include under reamed piles, used in softer strata, as well as
Augercast piles, which are often used when it is necessary to minimize noise pollution as well as in
environmentally sensitive sites. These unique piles are formed using hollow stemmed augers which
drill down to a predetermined depth, following which cement if flowed down through the stem,
and the auger is withdrawn, allowing the drilled space to fill up directly with cement. As the auger is
withdrawn, a column of fluid cement is formed within the drilled site, into which reinforcing cages
are commonly placed to ensure that the pile is strong enough to serve its purpose.
Importance of foundation design and analysis
Each structural challenge has its own parameters making foundation design and analysis a crucial element for all construction projects. Using CAD-based tools, Civil Engineers test these parameters to find out the correct way to approach the project. To help young Civil engineers get started on their career, Skyfi Labs is offering foundation design and analysis program as part of the ongoing Civil Simplified Summer Training Program. View details here. Foundation Engineering of Structures
Skyfi Labs
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Published:
2014-10-19 •
Last Updated:
2021-03-08
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