Civil Engineering Reference
In-Depth Information
To be practical, the piles must be of a type that will permit access for piling equipment
to the locations where they are required, the design must recognize the limits of what
is possible in current practice with regard to the equipment available, and the method
of construction must recognize and seek to minimize difficulties related to ground
conditions that could impede proper construction.
To be economic, the design should maximize the bearing capacity of each pile while
at the same time providing for an adequate margin of safety against failure or excessive
deformation of either individual piles or pile groups. The materials of the pile need
also to be reasonably stressed and not used wastefully.
It is sometimes thought that, for any particular ground conditions and structural
application, there is but one best choice of pile type that will result in sound and
durable results. However it is more often than not the case that any one of a number
of methods could be employed to yield a satisfactory end product and the real choice
may rest on such items as access for equipment, environmental disturbance, or on the
important consideration of overall cost. So many variables exist in practice, not least
being the detail of ground conditions, that it is not possible to produce a set of rules
that will invariably lead to easy identification of a best solution.
It is clear that the factors involved in making a best choice require knowl-
edge of ground conditions, equipment installation procedures, and materials, and
that several skills are needed on the part of both the designer and the contractor
carrying out the work. In so far as the usual practice of carrying out pile design,
selection and the implementation of the work is concerned, several procedures are
adopted. Some larger firms of consulting engineers with geotechnical skills carry
out pile design within their own companies and frequently discuss their require-
ments with specialist contractors in the process of formulating a solution. Other
structural engineers set out guidelines for pile design, perhaps stipulating settle-
ment or deformation requirements and occasionally specifying the type of pile that
they consider appropriate. They then leave detailed design in the hands of specialist
contractors with a request for competitive quotations. Yet others provide a pile
design for the works, but leave specialist contractors the option of submitting an
alternative scheme based on any other proposal that will achieve the same ends.
Each of these approaches can work satisfactorily in practice, but there is a need
to recognize that certain skills and experience are necessary on the part of those
involved, and full information to allow both proper design and construction must
be made available to all those involved. Many contractual disputes centre around
inappropriate site investigation, unfortunate pile type selection, bad specification
or ill informed supervision and the scene is set for difficulty at the very start of
the work.
10.2 Limitations on method choice imposed by
ground conditions
10.2.1 Water and rocks
It is clear that a proper choice of piling method can only be based on adequate site
investigation and on a knowledge of the geology and history of use of the site in
question. Without such an appreciation serious difficulties may be encountered at
